diktat java console
TRANSCRIPT
Java Programming (Console)
Hands on Lab
September 2011
For the latest information, please see bluejack.binus.ac.id
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Table of Contents
OVERVIEW ..................................................................................................... iii Chapter 01 ...................................................................................................... 1 Introduction to Java Programming ...................................................................... 1 Chapter 02 .................................................................................................... 13 Data Type and I/O.......................................................................................... 13 Chapter 03 .................................................................................................... 34 Arithmetic Operation ...................................................................................... 34 Chapter 04 .................................................................................................... 42 Selection Statement ....................................................................................... 42 Chapter 05 .................................................................................................... 53 Iteration Statement, Jump Operator ................................................................. 53 Chapter 06 .................................................................................................... 62 Exception Handling ......................................................................................... 62 Chapter 07 .................................................................................................... 71 Array ............................................................................................................ 71 Chapter 08 .................................................................................................... 91 Methods ........................................................................................................ 91 Chapter 09 .................................................................................................. 107 Recursion .................................................................................................... 107 Chapter 10 .................................................................................................. 121 Sorting ....................................................................................................... 121 Chapter 11 .................................................................................................. 133 Utility ......................................................................................................... 133 Chapter 12 .................................................................................................. 145 Introduction to OOP Concept ......................................................................... 145 Chapter 13 .................................................................................................. 148 Class and Object .......................................................................................... 148 Chapter 14 .................................................................................................. 156 Encapsulation .............................................................................................. 156 Chapter 15 .................................................................................................. 174 Inheritance .................................................................................................. 174 Chapter 16 .................................................................................................. 196 Polymorphism .............................................................................................. 196 Chapter 17 .................................................................................................. 222 Abstract and Interface .................................................................................. 222 Chapter 18 .................................................................................................. 240 Package ...................................................................................................... 240 Chapter 19 .................................................................................................. 259 Basic Class in Java ....................................................................................... 259 Chapter 20 .................................................................................................. 271 Data Structure in Java .................................................................................. 271 Chapter 21 .................................................................................................. 282 File ............................................................................................................. 282 Chapter 22 .................................................................................................. 295 Thread ........................................................................................................ 295 Chapter 23 .................................................................................................. 301 Generic ....................................................................................................... 301
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OVERVIEW
Chapter 01
• Introduction to Java Programming
Chapter 02
• Data Type and I/O
Chapter 03
• Arithmetic Operation
Chapter 04
• Selection Statement
Chapter 05
• Iteration Statement, Jump Operator
Chapter 06
Exception Handling
Chapter 07
• Array : One Dimentional Array, Two Dimentional Array and Ragged Array
Chapter 08
• Methods
Chapter 09
• Recursion
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Chapter 10
• Sorting : Using Bubble Sort, Selection Sort, Insertion Sort, and Merge Sort
Chapter 11
• Utility : Using Execution Delay, Java Random C, Currency, Calendar, and Timer Class
Chapter 12
• Introduction to OOP Concept
Chapter 13
• Class and Object
Chapter 14
• Encapsulation
Chapter 15
• Inheritance
Chapter 16
• Polymorphism
Chapter 17
• Abstract and Interface
Chapter 18
• Package
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SYSTEM REQUIREMENT
Hardware:
o Minimum:
1.6 GHz CPU, 192 MB RAM, 1024x768 display, 5400 RPM hard disk
o Recommended:
2.2 GHz, 384 MB, 1280x1024 display, 7200 RPM or higher.
o On Windows Vista:
2.4 GHz CPU, 768 MB RAM
Software:
o Textpad 5
o Eclipse
o 1.3 GB of available disk space for the full install
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Chapter 01
Introduction to Java Programming
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Introduction to Java IDE and Java Editor [Eclipse and Netbeans]
An integrated development environment (IDE) (also known as integrated
design environment or integrated debugging environment) is a software
application that provides comprehensive facilities to computer programmers for software
development. An IDE normally consists of:
a source code editor
a compiler and/or an interpreter
build automation tools
a debugger
Sometimes a version control system and various tools are integrated to simplify
the construction of a GUI. Many modern IDEs also have a class browser, an object
inspector, and a class hierarchydiagram, for use with object-oriented software
development. There are many Java IDE such as Dr.Java,BlueJ,NetBeans, IntelliJ IDEA,
Eclipse,Oracle JDeveloper, XinoxJCreator.
NetBeans refers to both a platform framework for Java desktop applications,
and an integrated development environment (IDE) for developing with Java, JavaScript,
PHP, Python, Ruby, Groovy, C, C++, Scala, Clojure, and others.
The NetBeans IDE is written in Java and can run anywhere a JVM is installed,
including Windows, Mac OS, Linux, and Solaris. A JDK is required for Java development
functionality, but is not required for development in other programming languages.
The NetBeans Platform allows applications to be developed from a set of modular
software components called modules. Applications based on the NetBeans platform
(including the NetBeans IDE) can be extended by third party developers.
Eclipse is a multi-language software development environment comprising an
integrated development environment (IDE) and an extensible plug-in system. It is
written mostly in Java and can be used to develop applications in Java and, by means of
various plug-ins, other programming languages including Ada, C, C++, COBOL, Perl,
PHP, Python, Ruby (including Ruby on Rails framework), Scala, Clojure, and Scheme.
The IDE is often called Eclipse ADT for Ada, Eclipse CDT for C/C++, Eclipse JDT for Java,
and Eclipse PDT for PHP.
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Introduction to Java Language
Java is a programming language originally developed by James Gosling at Sun
Microsystems (which is now a subsidiary of Oracle Corporation) and released in 1995 as
a core component of Sun Microsystems' Java platform. The language derives much of its
syntax from C and C++ but has a simpler object model and fewer low-level facilities.
Java applications are typically compiled to bytecode (class file) thatcan run on any
Java Virtual Machine (JVM) regardless of computer architecture. Java is a general-
purpose, concurrent, class-based, object-oriented language that is specifically designed
to have as few implementation dependencies as possible. It is intended to let application
developers "write once, run anywhere".
Java is currently one of the most popular programming languages in use, and is
widely used from application software to web applications.
The original and reference implementation Java compilers, virtual machines, and
class libraries were developed by Sun from 1995. As of May 2007, in compliance with
the specifications of the Java Community Process, Sun relicensed most of its Java
technologies under the GNU General Public License. Others have also developed
alternative implementations of these Sun technologies, such as the GNU Compiler for
Java, GNU Classpath, and Dalvik.
One characteristic of Java is portability, which means that computer programs
written in the Java language must run similarly on any supported hardware/operating-
system platform. This is achieved by compiling the Java language code to an
intermediate representation called Java bytecode, instead of directly to platform-specific
machine code. Java bytecode instructions are analogous to machine code, but are
intended to be interpreted by a virtual machine (VM) written specifically for the host
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hardware. End-users commonly use a Java Runtime Environment (JRE) installed on their
own machine for standalone Java applications, or in a Web browser for Java applets.
Standardized libraries provide a generic way to access host-specific features such
as graphics, threading, and networking.
A major benefit of using bytecode is porting. However, the overhead of
interpretation means that interpreted programs almost always run more slowly than
programs compiled to native executables would. Just-in-Time compilers were introduced
from an early stage that compilebytecodes to machine code during runtime.
Advantages of JAVA
1. JAVA offers a number of advantages to developers.
2. Java is simple: Java was designed to be easy to use and is therefore easy to
write, compile, debug, and learn than other programming languages. The reason
that why Java is much simpler than C++ is because Java uses automatic memory
allocation and garbage collection where else C++ requires the programmer to
allocate memory and to collect garbage.
3. Java is object-oriented: Java is object-oriented because programming in Java is
centered on creating objects, manipulating objects, and making objects work
together. This allows you to create modular programs and reusable code.
4. Java is platform-independent: One of the most significant advantages of Java is
its ability to move easily from one computer system to another.
5. The ability to run the same program on many different systems is crucial to
World Wide Web software, and Java succeeds at this by being platform-
independent at both the source and binary levels.
6. Java is distributed: Distributed computing involves several computers on a
network working together. Java is designed to make distributed computing easy
with the networking capability that is inherently integrated into it.
7. Writing network programs in Java is like sending and receiving data to and from
a file. For example, the diagram below shows three programs running on three
different systems, communicating with each other to perform a joint task.
8. Java is interpreted: An interpreter is needed in order to run Java programs. The
programs are compiled into Java Virtual Machine code called bytecode.
9. The bytecode is machine independent and is able to run on any machine that has
a Java interpreter. With Java, the program need only be compiled once, and the
bytecode generated by the Java compiler can run on any platform.
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10. Java is secure: Java is one of the first programming languages to consider
security as part of its design. The Java language, compiler, interpreter, and
runtime environment were each developed with security in mind.
11. Java is robust: Robust means reliable and no programming language can really
assure reliability. Java puts a lot of emphasis on early checking for possible
errors, as Java compilers are able to detect many problems that would first show
up during execution time in other languages.
12. Java is multithreaded: Multithreaded is the capability for a program to perform
several tasks simultaneously within a program. In Java, multithreaded
programming has been smoothly integrated into it, while in other languages,
operating system-specific procedures have to be called in order to enable
multithreading. Multithreading is a necessity in visual and network programming.
Disadvantages of JAVA
1. Performance: Java can be perceived as significantly slower and more memory-
consuming than natively compiled languages such as C or C++.
2. Look and feel: The default look and feel of GUI applications written in Java using
the Swing toolkit is very different from native applications. It is possible to
specify a different look and feel through the pluggable look and feel system of
Swing.
3. Single-paradigm language: Java is predominantly a single-paradigm language.
However, with the addition of static imports in Java 5.0 the procedural paradigm
is better accommodated than in earlier versions of Java.
Compile, Run & Debug
Compile,Run and Debug in Java we can use Java Compiler.A Java compiler is a
compiler for the Java programming language. The most common form of output from a
Java compiler areJava class files containing platform-neutral Java bytecode. There exist
also compilers emitting optimized native machine code for a particular
hardware/operating system combination.
Most Java-to-bytecode compilers, likes being a well-known exception, do virtually
no optimization, leaving this until runtime to be done by the JREThe Java Virtual
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Machine (JVM) loads the class files and either interprets the bytecode or just-in-time
compiles it to machine code and then possibly optimizes it using dynamic compilation.
The very first Java compiler developed by Sun Microsystems was written in C
using some libraries from C++.
To compile and run Java programs on your computer, you need to have a
working installation of the Java Development Kit (JDK) from Sun Microsystems. The JDK
includes command-line commands to compile and run Java programs.
Java program normally go through five phases. These are:
Compile Edit Load Verify Execute
Java Bytecode
JVM
Any Computer
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Creating a Java Application
After learning the theory about Java Language, let’s start learning how to make a
simple Java Application by creating the classic ―Hello World‖ Program.
First, open up your editor and write these line of codes in your editor.
publicclass Main {
publicstaticvoid main(String[] args) {
System.out.println("Hello World!");
}
}
As you can see in the code above, Java code mainly has two main parts :
1. The public class parts, this is called Class Definition, because Java is an
Object Oriented Programming Language all Java Program is builtfrom a class.
2. The public static void main parts, this is the main() method where all Java
program is being invoked, all code in main() method will be executed first when
your program runs.
You will see on the code above, the Syntax we use to print something to our
console window is the System.out.println("Hello World!");this code will print ―Hello
World!‖ in your console window!
1. Exercise
Q: What is JVM used for?
A: Java Virtual Machine (JVM) is used for enabling a set of computer software
programs and data structures to use a virtual machine model for the execution of other
computer programs and scripts.
Q: Mention five primary goals in the creation of the Java language!
A:
1. It should be "simple, object-oriented, and familiar".
2. It should be "robust and secure".
3. It should be "architecture neutral and portable".
4. It should execute with "high performance".
5. It should be "interpreted, threaded, and dynamic".
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Q :What releases of Java technology are currently available? What do they
contain?
A: The Java programming language is currently shipping from Sun Microsystems, Inc. as
the Java 2 SDK and Java 2 Runtime Environment. All Sun releases of the Java 2 Platform
software are available from the Java 2 Platform software home page
(http://java.sun.com/j2se/).
Each release of the Java 2 SDK, Standard Edition contains:
Java Compiler
Java Virtual Machine*
Java Class Libraries
Java AppletViewer
Java Debugger and other tools
Documentation (in a separate download bundle)
Q : Write simple program to print ―Hello World‖ to the console window!
A :
A. Task 01 - Create Java Project in Eclipse Editor
in this tutorial we will use Eclipse as our Java editor, this task show you how to
run Eclipse and make your first Java Project
i. Run Eclipse from Start Menu
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ii. On the Eclipse Menu, Open File New Project
iii. On Project Window, choose Java Project and click Next
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iv. Enter name of project,click Next and Finish
v. On tree panel on the left side window, expand your Project folder
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vi. Right click on the srcfolder on your Project tree and create New Class
vii. Enter the Name of your Java Class on the field below
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viii. Then press Finish
B. Task 02 – Write your first code to on your new class
publicclass Main {
publicstaticvoid main(String[] args) {
System.out.println("Hello World");
}
}
As we explained above, the Java program consist of two main parts, the Class
Definition and the main() method. The Class Definition is needed in all of Java
Program, and the main() method is required because all Java program is invoked from
this program.
The System.out.println("Hello World");is used to print a text to your
console window, more about this syntax will be covered on the next Chapter.
C. Task 03 – Run your first Java Application
After we write our first Java Code, the next step to make our program run is to
Compile our code so it will be a bytecode that will be running on the JVM.
In Eclipse use [CTRL] + [F11] Key to run your Java Project, and you will see the
Output of your code. Congratulations on making your very first Java Program!
Output :
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Chapter 02
Data Type and I/O
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Constants & Variables
The term variable is used because the data stored in a variable can vary. In other
words, you can change the value of a variable. In Java, you use the assignment operator
= to assign a variable to a particular value. For example, the following statements
declare an integer x and assign it the value 12.
int x;
x = 12;
Note that a variable can assign a value at the time it is declared. The previous
two statements could have been replaced with the following single statement:
int x = 12;
Java is strict about letting you assign variables only to values that match the
variable’s data type. If x is an int, you cannot assign it to other data types unless you
use the cast operator. For example, the following statements declare x as an int and
then attempt to assign x to a floating-point value.
int x;
double d = 3.5;
x = d; //This does not compile!
x = (int)d; //This does compile since I used the cast operator.
The final keyword is used in Java to declare a variable as a constant. Afinal in
Java cannot be changed after it is assigned a value. Consider the following statements,
some of which compile and some of which don’t.
final doublePI = 3.14159;
PI = -5.0; //Does not compile!
finalint x;//A blank final
x = 12; //ok
x = 100 //Does not compile!
The variable PI is declared final and initialized to 3.14159, so attempting to
change it to –5.0 is not valid. The variable x is declared final, but is not initialized. This
can be done in Java, and x is referred to as a blank final. Assigning it to 12 at a later
time is valid, but it cannot be changed after it is assigned. Trying to change it to 100 is
invalid and causes a compile error.
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Data Type
After learning about variable to store our data, we will learn about Data Type,
every variable must have a type which defines what values that variable can hold. The
variable type can be one of three things:
1. Primitive Data Type
2. Name of a Class or Abstract Data Type
3. An Array
In general Data Type is divided in 2, the Primitive Data Type and Abstract
Data Type and we will talk about Array in later chapter.
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Primitive Data Type
In the table above is a list of the primitive data types in Java. The primitive types
are the building blocks for more complicated types. Like its predecessor languages C and
C++ and what we me mentioned above,Java requires all variables to have a type before
they can be used in a program. For this reason,Java is referred to as a strongly typed
language.
In C and C++ programs, programmers frequently had to write separate versions
of programs to support different computer platforms, because the primitive data types
were not guaranteed to be identical from computer to computer. For example, an int
value on one machine might be represented by 16 bits (2 bytes) of memory, while an
int value on another machine might be represented by 32 bits (4 bytes) of memory. In
Java, int values are always 32 bits (4 bytes).
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Each data type in the list above is listed with its size in bits (there are eight bits
to a byte)and its range of values (the data range they can hold). Because the designers
of Java want it to be maximally portable, they chose to use internationally recognized
standards for both character formats (Unicode) and floating-point numbers (IEEE 754).
When instance variables of the primitive data types are declared in a class, they
areautomatically assigned default values unless specified otherwise by the
programmer.Instance variables of types char, byte, short, int, long, float and double
are all given the value 0 by default. Variables of type boolean are given the value false
by default.
Abstract Data Type
What is an abstract data type? Consider the built-in type int. What comes to
mind is the notion of an integer in mathematics, but int on a computer is not precisely
what an integer is in mathematics. In particular, computer int are normally quite limited
in size.
For example, inton a 32-bit machine is limited approximately to the range –2
billion to +2 billion. If the result of a calculation falls outside this range, an error occurs
and the machine responds in some machine-dependent manner, including the possibility
of ―quietly‖producing an incorrect result. Mathematical integers do not have this
problem. So the notion of a computer int is really only an approximation to the notion of
a real-world integer. The same is true with float.
The point is that even the built-in data types provided with programming
languages like Java are really only approximations or models of real-world concepts and
behaviors.
We have taken intfor granted until this point, but now you have a new
perspective to consider. Types like int, float, char and others are all examples of
abstract data types. They are essentially ways of representing real-world notions to
some satisfactory level ofprecision within a computer system.
Java has four integer types: byte, short, int, and long. Use the type that is
most appropriate for your needs. Java has two floating-point types: float and double.
The double type is twice as big as float. So, the double is known as double precision,
float as single precision. The double type is more accurate than the float type.
The float and double types are called floating-point because they are stored in
scientific notation. Number such as 50.534 is stored as 5.0534e+1, its decimal point is
floated to a new position.
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An abstract data type actually captures two notions, namely a data
representation and the operations that are allowed on that data. For example, the notion
of intdefines addition,subtraction, multiplication, division and modulus operations in
Java, but division by zero is undefined.
Another example is the notion of negative integers whose operations and data
representation are clear, but the operation of taking the square root of a negativeinteger
is undefined. In Java, the programmer uses classes to implement abstract data types.
Java has a small set of primitive types. ADTs extend the base programming language.
Assignment Statement and Expression
A statement is the simplest thing you can do in Java; a statement forms a single
Java operation. All the following are simple Java statements:
inti = 1;
importjava.awt.Font;
System.out.println(“This motorcycle is a “+ color + “ “ + make);
m.engineState = true;
Statements sometimes return values—for example, when you add two numbers
together or test to see whether one value is equal to another. Or when you called a
method to round some floating number, the method will return the rounded number,
and that’s what we called as return values.
The most important thing to remember about Java statements is that every
statement ends with a semicolon. Forget the semicolon and your Java program won’t
compile.Java also has compound statements, or blocks, which can be placed wherever a
single statement can. Block statements are surrounded by braces ({}).
Conversion (Type Casting)
The cast operator can be used to cast primitive data types. For example, suppose
that you have a double that you want to store in a float. Even if the double fits easily in
the float, the compiler still requires you to use the cast operator:
double pi = 3.14159;
float a = pi; //Does not compile!
float b = (float) pi; //Works fine
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You might think the compiler should be smart enough to realize that 3.14159 fits
into a float, so no casting is necessary; however, it is important to realize that the
compiler only knows data types. When you assign a 64-bit double to a 32-bit float, the
compiler only sees a larger piece of data being stored in a smaller piece. Because data
could be lost, the cast operator tells the compiler you know what you are doing, and any
loss of data is acceptable.
ASCII
The American Standard Code for Information Interchange (ASCII) is a
character-encoding scheme based on the ordering of the English alphabet. ASCII codes
represent text incomputers, communications equipment, and other devices that use
text. Most modern character-encoding schemes are based on ASCII, though they
support many more characters than did ASCII.
This is an example of ASCII Table :
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Naming Convention
A naming convention is a rule to follow as you decide what to name your
identifiers (e.g. class, package, variable, method, etc).
Why Use Naming Conventions?
Different Java programmers can have different styles and approaches to the way
they program. By using standard Java naming conventions they make their code easier
to read for themselves and for other programmers. Readability of Java code is important
because it means less time is spent trying to figure out what the code does, leaving
more time to fix or modify it.
To illustrate the point it's worth mentioning that most software companies will
have a document that outlines the naming conventions they want their programmers to
follow. A new programmer who becomes familiar with those rules will be able to
understand code written by a programmer who might have left the company many years
before hand.
Standard Java Naming Conventions
The below list outlines the standard Java naming conventions for each type:
Identifier:For naming variables, constants, methods, classes, and packages.
Descriptive identifiers make programs easy to read.
A sequence of characters that consists of letters, digits,
underscores (_), and dollar signs ($).
Must start with a letter, an underscore (_), or a dollar sign
($). It can’t start with a digit.
Can’t be a reserved word (keyword), true, false, or null.
Can be of any length.
Case sensitive, area, Area, and AREA are all different
identifiers.
Suggested to not name identifiers with the $ character
(although possible). The $ character should be used only in
mechanically generated source code.
Classes: Names should be in CamelCase. Try to use nouns because a class
is normally representing something in the real world:
class Customer
class Account
Interfaces: Names should be in CamelCase. They tend to have a name that
describes an operation that a class can do:
interface Comparable
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interface Enumerable
Note that some programmers like to distinguish interfaces by beginning the name with
an "I":
interface IComparable
interface IEnumerable
Methods: Names should be in mixed case. Use verbs to describe what the
method does:
void calculateTax()
String getSurname()
Variables: Used to store values to be used later in a program. Their values
can be changed. Names should be in mixed case. The names should represent
what the value of the variable represents:
StringfirstName
intorderNumber
Only use very short names when the variables are short lived, such as in for
loops:
for(inti=0; i<20;i++)
{
//i only lives in here
}
Constants: Permanent data that nevers changes. Names should be in
uppercase.
static final int DEFAULT_WIDTH
static final int MAX_HEIGHT
Imports
The imports directive tells the compiler where to look for the class definitions
when it comes upon a class that it cannot find in the default java.lang package. So, for
example,the import statements:
import mypack.*;
import mypack.extrapack.*;
import java.applet.*;
indicate that classes can be found in the mypack and mypack.extrapackpackages and
also that the Applet class can be found in the java.applet package.
Asteriks (*) in import mypack.*referstoalltypesthatexistin thepackagebutdoes
notincludea packagethat is inthepackage.
If you want include only one class in the package, you can also type import
mypack.MyClassstatement.
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Output
To print a text on Console Window in Java, you can use
System.out.printf(),System.out.print() or System.out.println() method.
println() is used to print a String and then add anewline at the end of the
sentences. Example:
The output will be:
print() is used to print a Stringwithout adding anewline at the end of the
sentences. Example:
The output will be:
In Java if you wantto print a String using user defined format,you can use
printf() or format().printf() or format() allows the programmer to specify
textual representations of data using two parameters:
a format String, or "template" and
anargument list, or a vector of data to be formatted according to the
template.
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The general syntax of a format specifier is:
%[flags][width][.precision][argsize]typechar
Flags
Flags are single characters that indicate exceptions to the conversion type's
default behavior. A format-specifier may have multiple flags, but some flags are
mutually exclusive. Multiple flags can appear in any order. The following table lists the
formatting flags supported by Java's printf classes:
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flag Meaning conversion types
applicable
'-' Result is left-aligned in the field. This flag is meaningless if no mandatory field width is specified.
%d, %u, %o, %x, %X, %z[n],
%Z[n], %f, %e, %E, %g, %G, %s,
%c, %p '^' Result is centered in the field. This flag is meaningless if no mandatory field width is specified.
'+' Non-negative values begin with a plus character ('+').
%d, %f
' ' Non-negative values begin with a space character (' '). This flag is only useful for signed conversion results (%d and %f).
'#'
Argument is represented in an "alternate form." This depends on the conversion type:
%o Non-negative octal values are prepended with a zero ('0').
%x, %X
Hexadecimal values are prepended with the prefix "0x" or "0X".
%e,
%E, %f
The integer portion of the result always ends with a decimal point ('.'), even if the fractional portion is zero.
%g, %G
The fractional portion always appears, even if it is zero.
%c If the character is special or unprintable, it is output in an escaped form. The output can be surrounded by single quotes to form a syntactically valid Java character literal.
There is no alternate form for %s, %d, %u, %z[n], and %Z[n]
Precision specifier
An optional "precision-specifier" may be included in a format-specifier to indicate
the precision with which to convert the data. The meaning of the word "precision"
depends on the type of conversion being performed:
conversion type meaning of "precision"
default value
(if omitted)
%d, %o, %u, %x, %X,
%z[n], %Z[n]
(integer conversions)
minimum number of digits. The converted value will be prepended with zeros if necessary. Note that if the precision is 0 and the value is zero, nothing will be printed, or the entire field will be nothing but padding.
1
%f, %e, %E, %g, %G
(real conversions)
number of fractional digits after the decimal point. The converted value will be rounded if necessary.
6
%s (strings) the maximum number of characters. If the string is too long, it will be truncated.
infinity
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If no precision is specified, the default precision will be used. Precision cannot be
specified for conversion types other than those listed above.
Width specifier
An optional "width specifier," if present, indicates the field with, or the minimum
number of characters in the output that the formatted argument will span. If the string
representation of the value does not fill the minimum length, the field will be left-padded
with spaces. If the converted value exceeds the minimum length, however, the
converted result will not be truncated.
Example: If the format specifier is "%6d", and the supplied int argument is 52, then the output will be " 52" (four spaces on the left).
If no width is specified, then there is no minimum size for the converted result.
The field will be only as large as necessary to display the result.
Conversion type character
Typechar is a single character identifying the conversion type. The supported
conversion types are listed below, along with their meanings, and the corresponding
arguments expected in the argument vector:
type character input String result
%d signed
int signed decimal integer
%u unsigned int
unsigned decimal integer
%o unsigned int
unsigned octal integer
%x, %X unsigned
int
unsigned hexadecimal integer, lowercase or
uppercase
%z[n], %Z[n] unsigned
int
unsigned integer base n, with n coded in
decimal; include square brackets
%f float real number, standard notation
%e, %E float real number, scientific notation (lowercase or
uppercase exponent marker)
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%g, %G float
same format as %f or %e, depending on the
value. Scientific notation is used only if the
exponent is greater than the precision or less
than -4.
%s String String
%c char character
%p Object object identity hash code (i.e., pointer value), in
unsigned hexadecimal
additional format specifiers that do not result in argument
conversions
%\n (none) platform-independent line separator
%n (null) counts characters
Example: long n = 461012;
System.out.format("%d%n", n); // --> "461012"
System.out.format("%08d%n", n); // --> "00461012"
System.out.format("%+8d%n", n); // --> " +461012"
System.out.format("%,8d%n", n); // --> " 461,012"
System.out.format("%+,8d%n%n", n); // --> "+461,012"
double pi = Math.PI;
System.out.format("%f%n", pi); // --> "3.141593"
System.out.format("%.3f%n", pi); // --> "3.142"
System.out.format("%10.3f%n", pi); // --> " 3.142"
System.out.format("%-10.3f%n", pi); // --> "3.142"
Escape Sequences
A character preceded by a backslash (\) is an escape sequence and has special
meaning to the compiler. The following table shows the Java escape sequences:
Escape Sequences
Escape
Sequence Description
\t Insert a tab in the text at this point.
\b Insert a backspace in the text at this point.
\n Insert a newline in the text at this point.
\r Insert a carriage return in the text at this point.
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\f Insert a formfeed in the text at this point.
\' Insert a single quote character in the text at this point.
\" Insert a double quote character in the text at this point.
\\ Insert a backslash character in the text at this point.
When an escape sequence is encountered in a print statement, the compiler
interprets it accordingly. For example, if you want to put quotes within quotes you must
use the escape sequence, \", on the interior quotes. To print the sentence:
She said "Hello!" to me.
you would write:
System.out.println("She said \"Hello!\" to me.");
Input
To get user input, use the BufferedReader and InputStreamReader
The InputStreamReader class reads the user's input.
The BufferedReader class buffers the user's input to make it work more efficiently.
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You can also use Scanner class to receive input, look at the example below:
If you want to receive input with data type int you cannot use
reader.nextLine(),
you must use reader.nextInt().Method that you can use:
nextInt()scans the next token of the input as an int.
nextFloat()scans the next token of the input as a float.
nextDouble()scans the next token of the input as a double.
nextByte()scans the next token of the input as a byte.
nextLong()scans the next token of the input as a long.
nextShort() scans the next token of the input as a short.
How did you write a program? Did you immediately begin to write the code? No.
It’s important to think before you type. Thinking enables you to generate a logical
solution for the problem without concern about how to write the code. Once you have a
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logical solution, type the code to translate the solution into a Java program. The
translation is not unique.
4. Exercise
Please make a simple program to learn some data type in Java.
1. Asking for input using Scanner class that imported from java.util.Scanner
Data type that will be inputed:
o int
o double
o String
o boolean
o char (obtained from the type casting of int that user input)
2. Show results from each input of the above in accordance with the example below.
Print Screen of the Program when Ask User to Input Data
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Print Screen of the Program when Show Result
a. Task 01 - Create Project Java in Eclipse
i. Run Eclipse from Start Menu
ii. Open Menu File -> New -> Project
iii. On Project Window, choose Java Project and click next
iv. Enter name of project,click next and finish
v. On tree panel on the left side window, expand Project folder
vi.Right click on src and create new class
vii. Enter the name class
viii. Then Press Finish
b. Task 02 – Using import and Declare Variable with Data Type
- Type import java.util.Scanner for input data
- Declare variable to save value and object from Scanner for receive input
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c. Task 03 – Receive input for any kind of data type
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d. Task 04 – Print variable using print format (Read “Formatted Output” in this
Chapter)
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Chapter 03
Arithmetic Operation
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Numerical Operators and Arithmetic Expression
Arithmetic expressions in Java must be written in straight-line form to facilitate
entering programs into the computer. Thus, expressions such as ―a divided by b‖ must
be written as a / b, so that all constants, variables and operators appear in a straight
line.
Parentheses are used in Java expressions in the same manner as in algebraic
expressions.
For example, to multiply a times the quantity b + c, we write
a * ( b + c )
Java applies the operators in arithmetic expressions in a precise sequence
determined by the following rules of operator precedence, which are generally the same
as those followed in algebra:
1. Operators in expressions contained within pairs of parentheses are evaluated
first. Thus, parentheses may be used to force the order of evaluation to occur in
any sequence desired by the programmer. Parentheses are at the highest level of
precedence.In cases of nested or embedded parentheses, the operators in the
inner mostpair of parentheses are applied first.
2. Multiplication, division and modulus operations are applied next. If an expression
contains several multiplication, division or modulus operations, the operators are
applied from left to right. Multiplication, division and modulus operators have the
same level of precedence.
3. Addition and subtraction operations are applied last. If an expression contains
several addition and subtraction operations, the operators are applied from left to
right. Addition and subtraction operators have the same level of precedence.
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The rules of operator precedence enable Java to apply operators in the correct
order. When we say that operators are applied from left to right, we are referring to the
associativity of the operators. We will see that some operators associate from right to
left. The table below will summarizesthese rules of operator precedence. This table will
be expanded as additional Java operators are introduced.
Shorthand Operator
Shorthand assignment operator provides two advantages
1. needs less typing
2. java compiler handles in an efficient way
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This is the summary of shorthand operator
Operation Operator Example Expansion
Assignment = a = 5 a = 5
Addition += a += 5 a = a + 5
Subtraction -= a -= 5 a = a - 5
Multiplication *= a *= 5 a = a * 5
Division /= a /= 5 a = a / 5
Modulus %= a %= 5 a = a % 5
Bitwise |= a |= 5 a = a | 5
inclusive OR
Bitwise ^= a ^= 5 a = a ^ 5
exclusive OR (XOR)
Bitwise <<= a <<= 5 a = a << 5
left-shift
Bitwise >>= a >>= 5 a = a >> 5
right-shift
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Increment and Decrement Operator
Java provides the unary increment operator, ++, and the unary decrement
operator, --.A program can increment the value of a variable called c by 1 using the
increment operator, ++, rather than the expression c = c + 1 or c += 1. If an
increment or decrement operator is placed before a variable, it is referred to as the pre-
increment or pre-decrement operator, respectively. If an increment or decrement
operator is placed after a variable, it is referred to as the post-increment or post-
decrement operator, respectively.
Pre-incrementing (pre-decrementing) a variable causes the variable to be
incremented (decremented) by 1, and then the new value of the variable is used in the
expression in which it appears. Post-incrementing (post-decrementing) the variable
causes the current value of the variable to be used in the expression in which it appears,
and then the variable value is incremented (decremented) by 1.
The example code below will demonstrates the difference between the pre-
incrementing version and the post-incrementing version of the ++increment operator.
Post-incrementing the variable c causes it to be incremented after it is used in the
System.out.println method call (line 13). Pre-incrementing the variable c causes it to
be incremented before it is used in the System.out.println method call (line 20).
The program displays the value of c before and after the ++operator is used. The
decrement operator (--) works similarly.
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4. Exercise
Please make a simple arithmetic calculation program with the following
conditions:
1. Input 2 number using class Scanner.
2. Doing some arithmetic operations with steps below :
Doing increasing operation, first number + second number.
Doing decreasing operation, first number – second number and second
number – first number.
Doing multiplication operation, first number * second number.
Doing division operation, first number / second number and second number
/ first number.
Doing modulus operation, first number % secondnumber and second
number % first number.
Print Screen of the Program when Ask to Input Number
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Print Screen of the program when show result of arithmetic operations
a. Task 01 - Create Project Java in Eclipse
i. Run Eclipse from Start Menu
ii. Open Menu File -> New -> Project
iii. On Project Window, choose Java Project and click next
iv. Enter name of project,click next and finish
v. On tree panel on the left side window, expand Project folder
vi.Right click on src and create new class
vii. Enter the name class
viii. Then Press Finish
b. Task 02 - Doing some arithmetic operations
- Type import java.util.Scanner for input data
- Declare variable to save value and object from Scanner for receive input.
Create object from class Scanner to retrive input from user called 'in'. we will use
some method from class Scanner to get the input from user.
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- Make some arithmetic operations
+ in here is used for connectingtext(String)withvariable
This is for addition operation
This is for Substraction operation
This is for Multiplication operation
This is for Division operation
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Chapter 04
Selection Statement
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Selection Control Structures and Logical Operator
A selection structure is used to choose among alternative courses of action in a
program.For example, suppose that the passing grade on an examination is 60 (out of
100). Then thepseudocode statement
If student’s grade is greater than or equal to 60.Print “Passed”
determines if the condition ―student’s grade is greater than or equal to 60‖ is true or
false.
If the condition is true, then ―Passed‖ is printed, and the next pseudocode
statement in orderis performed (remember that pseudocode is not a real programming
language.)
If thecondition is false, the Print statement is ignored, and the next pseudocode
statement in orderis performed.
Note that the second line of this selection structure is indented. Such indentation
is optional, but it is highly recommended, because it emphasizes the inherent structure
of structured programs. The Java compiler ignores white-space characters, like
blanks,tabs and newlines, used for indentation and vertical spacing. Programmers insert
these white-space characters to enhance program clarity.
The preceding pseudocodeif statement may be written in Java as
if( studentGrade>= 60 ) System.out.println( "Passed" );
Notice that the Java code corresponds closely to the pseudocode. This attribute is
aproperty of pseudocode that makes it a useful program development tool. The
statement inthe body of theifstructure outputs the character String"Passed" in the
commandwindow.
The flowchart below will illustrates the single-selection if structure. This
flowchartcontains what is perhaps the most important flowcharting symbol—the diamond
symbol,also called the decision symbol, which indicates that a decision is to be made.
The decisionsymbol contains an expression, such as a condition, that can be either true
or false.
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Thedecision symbol has two flowlines emerging from it. One indicates the
direction to be takenwhen the expression in the symbol is true; the other indicates the
direction to be taken whenthe expression is false. A decision can be made on any
expression that evaluates to a valueof Java’s booleantype (i.e., any expression that
evaluates to true or false).
Note that the ifstructure is a single-entry/single-exit structure. We will soon
learnthat the flowcharts for the remaining control structures also contain (besides small
circlesymbols and flowlines) only rectangle symbols, to indicate the actions to be
performed, anddiamond symbols, to indicate decisions to be made. This factor is
indicative of the action/decision model of programming we have been emphasizing
throughout this chapter.
We can envision seven bins, each containing only control structures of one of the
seventypes. These control structures are empty; nothing is written in the rectangles or
in the diamonds.
The programmer’s task, then, is to assemble a program from as many of each
typeof control structure as the algorithm demands, combining the control structures in
only twopossible ways (stacking or nesting) and then filling in the actions and decisions
in a mannerappropriate for the algorithm. In this chapter we discuss the variety of ways
in whichactions and decisions may be written.
If-Else Statement
The ifselection structure performs an indicated action only when the given
conditionevaluates to true; otherwise, the action is skipped. The if/else selection
structure allowsthe programmer to specify that a different action is to be performed
45 | P a g e
when the conditionis true rather than when the condition is false. For example, the
pseudocode statement
If student’s grade is greater than or equal to 60
Print “Passed”
else
Print “Failed”
printsPassedif the student’s grade is greater than or equal to 60 and prints Failedif
thestudent’s grade is less than 60. In either case, after printing occurs, the next
pseudocodestatement in sequence is performed. Note that the body of the elseis also
indented.
The indentation convention you choose should be carefully applied throughout
yourprograms. It is difficult to read programs that do not use uniform spacing
conventions.The preceding pseudocodeif/elsestructure may be written in Java as
if( studentGrade>= 60 )
System.out.println("Passed" );
else
System.out.println("Failed" );
Below is the flowchart to illustrates the flow of control in an if/else
structure.Once again, note that, besides small circles and arrows, the only symbols in
the flowchartare rectangles (for actions) and a diamond (for a decision). We continue to
emphasize thisaction/decision model of computing.
Imagine again a deep bin containing as many emptydouble-selection structures
as might be needed to build a Java algorithm. The programmer’sjob is to assemble the
selection structures (by stacking and nesting) with othercontrol structures required by
the algorithm and to fill in the empty rectangles and emptydiamonds with actions and
decisions appropriate to the algorithm being implemented.
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Switch statement
Only be used for data type byte, short, char, dan int and enum. Example :
switch (test)
{
casevalueOne:
resultOne;
break;
casevalueTwo:
resultTwo;
break;
casevalueThree:
resultThree;
break;
default: defaultresult;
}
In the switch statement, the test (a primitive type of byte, char, short, or int)
is compared with each of the case values in turn. If a match is found, the statement, or
statements after the test is executed. If no match is found, the default statement is
executed. The default is optional, so if there isn’t a match in any of the cases and default
doesn’t exist, the switch statement completes without doing anything.
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Note that the significant limitation of the switch in Java is that the tests and
values can be only simple primitive types (and then only primitive types that are
castable to int).
You cannot use larger primitive types (long, float) or objects within a switch,
nor can you test for any relationship other than equality. This limits the usefulness of
switch to all but the simplest cases; nested ifs can work for any kind of test on any type.
Here’s a simple example of a switch statement similar to the nested if shown earlier:
switch (oper)
{
case „+‟:
addargs(arg1,arg2);
break;
case „*‟:
subargs(arg1,arg2);
break;
case „-‟:
multargs(arg1,arg2);
break;
case „/‟:
divargs(arg1,arg2);
break;
}
Note the break statement included in every line. Without the explicit break,
once a match is made, the statements for that match and also all the statements further
down in the switch are executed until a break or the end of the switch is found (and
then execution continues after the end of the switch).
In some cases, this may be exactly what you want to do, but in most cases,
you’ll want to make sure to include the break so that only the statements you want to
be executed are executed.
One handy use of falling through occurs when you want multiple values to
execute the same statements. In this instance, you can use multiple case lines with no
result, and the switch willexecute the first statements it finds. For example, in the
following switch statement, the String ―x is an even number.‖ is printed if x has
values of 2, 4, 6, or 8. All other values of x print the String ―x is an odd number.‖
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switch (x)
{
case 2:
case 4:
case 6:
case 8:
System.out.println(“x is an even number.”);
break;
default: System.out.println(“x is an odd number.”);
}
Ternary Statement
Java has one ternary operator - Conditional Operator ?:
Generally it looks like this: condition ?op1 : op2. If condition is false, the
Statement evaluates as op2; otherwise (true), it evaluates as op1.Conditional operator
?can be grouped right-to-left.
The expression op1?op2:op3?op4:op5?op6 :op7 can be rewritten for easier
understanding like this: op1?op2:(op3?op4:(op5?op6:op7))
The conditional operator ?was introduced in many programming languages as a
shorthand replacement for the if-then-else conditional statement.
Another Example:
if (a > b) {
result = x;
}
else {
result = y;
}
This can be rewritten as the following ternary statement:
result= a > b ?x : y;
Nested Selection Statement
The if constructed in java can be nested. In other words, an if construct can be
present inside the body of another if construct.
Nested if/else structures test for multiple cases by placing if/else structures
inside if/else structures. For example, the following pseudocode statement prints A for
exam grades greater than or equal to 90, B for grades in the range 80 to 89, C for
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grades in the range 70 to 79, D for grades in the range 60 to 69 and F for all other
grades:
If student’s grade is greater than or equal to 90
Print “A”
else
If student’s grade is greater than or equal to 80
Print “B”
else
If student’s grade is greater than or equal to 70
Print “C”
else
If student’s grade is greater than or equal to 60
Print “D”
else
Print “F”
This pseudocode may be written in Java as
if( studentGrade>= 90 )
System.out.println("A" );
else
if( studentGrade>= 80 )
System.out.println("B" );
else
if( studentGrade>= 70 )
System.out.println("C" );
else
if( studentGrade>= 60 )
System.out.println("D" );
else
System.out.println("F" );
If studentGradeis greater than or equal to 90, the first four conditions will be
true, butonly the System.out.printlnstatement after the first test will be executed.
After thatparticular System.out.printlnis executed, the else part of the ―outer‖
if/elsestatement is skipped.
1. Exercise
Please make a program to find the grade of the student with the following conditions:
1. Input using class Scanner from java.util.Scanner.
2. The program begins by asking for five inputs below :
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First input is student’s name in the form of String.
Second input is gender in the form of boolean, where is true = male and false =
female.
Third input is Mid Exam score with range between 0 until 100 in the form of
int.
Fourth input is Final Exam score with range between 0 until 100 in the form of
int.
Fifth input is Independent Task score with range between 0 until 100 in the
form of int.
3. Final score calculating with percentage 30 % Mid Exam, 50% Final Exam
and20% Independent Task.
4. Grade calculating is obtained from final score with the following conditions:
Grade A : final score >= 85
Grade B : 75<= final score <85
Grade C : 65<= final score <75
Grade D : 55<= final score <65
Grade E : final score <55
5. Provide message for each grade with the following provisions:
Grade A : ―Very good, Keep your grade‖
Grade B : ―Pretty good, Increase again‖
Grade C : ―Quite less,need to learn more‖
Grade D : ―Your score is not satisfy‖
Grade E : ―Learn more diligent and active‖
6. Each comment ends with Mr. for male gender, and Mrs. for female gender, plus the
name of student.
Print Screen of the Program Ask User to input Five Inputs
Print Screen of the Program after Calculating Score Result
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v. On tree panel on the left side window, expand Project folder
c. Task 03 – Calculate Final score from 30 % Mid Exam, 50% Final Exam and 20%
Independent Task.
d. Task 04 - Grade calculating is obtained from final score
Grade A : final score >= 85
Grade B : 75<= final score <85
Grade C : 65<= final score <75
Grade D : 55<= final score <65
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Grade E : final score <55
f. Task 06 - Print comment ends with Mr. for male gender, and Mrs. for female gender,
plus the name of student.
First I determine the comment ends with Mr or Mrs
In this selection , I use ternary operation
And then print comment ends Mr or Mrs, plus name of student
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Chapter 05
Iteration Statement, Jump Operator
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Repetition with While
If you can write programs using loops, you know how to program! A repetition
structure allows the programmer to specify that an action is to be repeated while some
condition remains true.
Structure for while
while( condition )
{
Statement
}
The pseudocodestatement :
While there are more items on my shopping list
Purchase next item and cross it off my list
describes the repetition that occurs during a shopping trip. The condition ―there are
moreitems on my shopping list‖ may be true or false. If it is true, then the action
―Purchase nextitem and cross it off my list‖ is performed.
This action will be performed repeatedly while the condition remains true. The
statement(s) contained in the whilerepetition structure constitute the body of the
whilestructure. The body of the whilestructure may be a single statement or a block.
Eventually, the condition will become false (when the last item on the shopping list has
been purchased and crossed off the list). At this point, the repetition terminates, and the
first pseudocode statement after the repetition structure is executed.
As an example of a whilestructure, consider a program segment designed to find
the first power of 2 larger than 1000. Suppose that the intvariable product has been
initialized to 2. When the following while structure finishes executing, product
containsthe result:
intproduct = 2;
while( product <= 1000 )
product = 2 * product;
The flowchart below will illustrates the flow of control of the preceding while
repetition structure. Once again, note that, besides small circles and arrows, the
flowchart contains only a rectangle symbol and a diamond symbol.
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Imagine, again, a deep bin of empty while structures that may be stacked and
nested with other control structures to form a structured implementation of an
algorithm’s flow of control. The empty rectangles and diamonds are then filled in with
appropriate actions and decisions.
The flowchart clearly shows the repetition. The flowline emerging from the
rectangle wraps back to the decision, which is tested each time through the loop until
the decision eventually becomes false. At this point, the while structure is exited, and
control passes to the next statement in the program.
When the while structure is entered, product is 2. Variable product is
repeatedly multiplied by 2, taking on the values 4, 8, 16, 32, 64, 128, 256, 512 and
1024 successively.
When product becomes 1024, the condition product <= 1000 in the
whilestructure becomes false. This result terminates the repetition, with 1024 as
product’s final value. Execution continues with the next statement after the while.
[Note: If a while structure’s condition is initially false, the body statement(s) will never
be performed]
Repetition with Do-While
The do/while repetition structure is similar to the while structure. In the while
structure,the program tests the loop-continuation condition at the beginning of the loop,
before performing the body of the loop. The do/while structure tests the loop-
continuation condition after performing the body of the loop; therefore, the loop body
always executes atleast once.
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When a do/while structure terminates, execution continues with the statement
after the while clause. Note that it is not necessary to use braces in the do/while
structure if there is only one statement in the body. However, most programmers
include the braces, to avoid confusion between the while and do/while structures. For
example,
while( condition )
normally is the first line of a whilestructure. A do/while structure with no braces
around a single-statement body appears as
do
statement
while( condition );
which can be confusing. Reader may misinterpret the last linewhile(condition );as a
while structure containing an empty statement (the semicolon by itself). Thus, toavoid
confusion, the do/while structure with one statement often is written as follows:
do{
statement
} while ( condition);
This is the flowchart for do/while repetition structure.
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Repetition with For
The forrepetition structure handles all of the details of counter-controlled
repetition. The forstructure’s first line (including the keyword for and everything in
parentheses after for) is sometimes called the for structure header. Notice that the
forstructure ―does it all‖: It specifies each of the items needed for counter-controlled
repetition with a control variable. If there is more than one statement in the body of the
forstructures, braces ({}) are required to define the body of the loop. Look at the
picture below:
The general format of the for structure is
for( expression1; expression2; expression3 )
statement
whereexpression1names the loop’s control variable and provides its initial
value,expression2is the loop-continuation condition (containing the control variable’s
final value) and expression3modifies the value of the control variable, so that the loop
continuation condition eventually becomes false.
Make sure that the loop-continuation-condition eventually becomes false so that
the program will terminate. A common programming error involves infinite loops
because of mistake in the loop-continuation-condition. Programmers often make
mistakes to execute a loop one more or less time (known as the off-by-one error). For
example, using count <= 100 is different with count < 100.
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Break Operation
The breakstatements alter the flow of control. The break statement,when
executed in a while, for, do/while or switch structure, causes immediate exit from
that structure. Execution continues with the first statement after the structure. Example:
for(int i = 0; i < 13; i ++){
System.out.println(i);
if(i == 7) break;
}
System.out.println("finish");
In the example if i has reached value 7 loop is automatically stop.And then the output is
0
1
2
3
4
5
6
7
Continue Operation
The continue statement proceeds with the next iteration (repetition) of the
immediately enclosing while, for or do/while structure. The labeled
continuestatement, when executed in a repetition structure (while, for or do/while),
skips the remaining statements in that structure’s body and any number of enclosing
repetition structures and proceeds with the next iteration of the enclosing labeled
repetition structure. Example:
for(int i = 0; i < 10; i ++){
if(i == 7) continue;
System.out.println(i);
}
System.out.println("finish");
In the example if i has reached value 7 the loop will skip the statement and continue the
loop
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The output is
0
1
2
3
4
5
6
8
9
10
Label Operation
We can also add alabel keywordbeforewhile, do-while orfor statement block and
put the label that we make before after continue or break statement, this method is
calledbreak with label. Usually label is used to break a loop and start from specific point.
Example:
loop1: //label
for(int i = 0; i < 10; i++){// 1st loop
for(int j = 0; j < 10; j++){// 2nd loop
//go out from 1st loop
if(map[i][j] == 1) break loop1;
}
}
System.out.println("finish");
Some programming languages have a goto statement. The goto statement
indiscriminately transfer control to any statement in the program and executes it. This
makes your program vulnerable to errors. The break and continue statements in Java
are different from goto statements. They operate only in a loop or a switch statement.
The break statement breaks out of the loop, and the continue statement breaks out of
the current iteration in the loop.
1. Exercise
Please make a program to print Odd and Even Number:
1. The program begins by asking user to input how many number they want to print
2. Print Odd and Even Number according to how many number that user input
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Print Screen of the Program Ask User to input count of number
Print Screen of the Program print all result
a. Task 01 - Create Project Java in Eclipse
v. On tree panel on the left side window, expand Project folder
c. Task 03 - Print Odd and Even Number according to count of number that user input
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Initialization: It allows the variable to be initialize
Termination (or condition): It allows to check the certain condition,the condition
according to user input
Increment: It allows the how much increase the given variable.
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Chapter 06
Exception Handling
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Exception Handling Definition
Exception handling is provided to enable programs to catch and handle errors
rather than letting them occur and suffering the consequences. Exception handling is
designed for dealing with synchronous errors such as an attempt to divide by zero (that
occurs as the program executes the divide instruction). Exception handling is not
designed to deal with asynchronous events such as disk I/O completions, network
message arrivals, mouse clicks, keystrokes and the like; these are best handled through
other means, such as Java event listeners.
Java exception handling enables a program to catch all exceptions, all exceptions
of a certain type or all exceptions of related types. This flexibility makes programs more
robust by reducing the likelihood that programs will not process problems during
program execution.
Exception handling is used in situations in which the system can recover from the
malfunction that caused the exception. The recovery procedure is called an exception
handler. The exception handler can be defined in the method that may cause an
exception or in a calling method.
Exception handling should be used:
to process exceptional situations where a method is unable to complete its task for
reasons it cannot control
to process exceptions from program components that are not geared to handling
those exceptions directly, or
on large projects to handle exceptions in a uniform manner project wide.
Try and Catch
An exception that occurs in a try block normally is caught by an exception
handler specified by a catch block immediately following that try block as in
try{
statements that may throw an exception
}
catch(ExceptionTypeexceptionReference) {
statements to process an exception
}
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A try block can be followed by zero or more catch blocks. If a try block executes
and no exceptions are thrown, all the exception handlers are skipped and control
resumes with the first statement after the last exception handler.
When an exception is thrown, control exits the current try block and proceeds to
an appropriate catch handler (if one exists) after that try block. It is possible that the
throw point could be in a deeply nested scope within a try block; control will still
proceed to the catch handler. It is also possible that the throw point could be in a
deeply nested method call; still, control will proceed to the catch handler.
A try block may appear to contain no error checking and include no throw
statements,but methods called from the try block may throw exceptions. Also,
statements in a try block that do not invoke methods may cause exceptions. For
example, a statement that performs array subscripting on an array object throws an
ArrayIndexOutOfBoundsExceptionif the statement specifies an invalid array
subscript. Any method call can invoke code that might throw an exception or call
another method that throws an exception.
Finally
The finally block is optional. If it is present, it is placed after the last of a try
block’scatch blocks, as follows:
try{
statements
resource-acquisition statements
}
catch( AKindOfException exception1 ) {
exception-handling statements
}
catch( AnotherKindOfException exception2 ) {
exception-handling statements
}
finally{
statements
resource-release statements
}
Java guarantees that a finally block (if one is present) will execute regardless of
whether any exception is thrown in the corresponding try block or any of its
corresponding catch blocks. Java also guarantees that a finally block (if one is present)
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will execute if a try block exits via a return, break or continue statement. If no
exception arises in the try block, finally block is also executed.
Resource-release code is placed in a finally block. Suppose a resource is
allocated in a try block. If no exception occurs, the catch handlers are skipped and
control proceeds to the finally block, which frees the resource. Control then proceeds to
the first statement after the finally block.
If an exception occurs, the program skips the rest of the try block. If the
program catches the exception in one of the catch handlers, the program processes the
exception. Then the finally block releases the resource, and control then proceeds to
the first statement after the finally block.
If an exception that occurs in the try block cannot be caught by one of the catch
handlers, the program skips the rest of the try block and control proceeds to the finally
block, which releases the resource. Then the program passes the exception up the call
chainuntil some calling method chooses to catch it. If no method chooses to deal with it,
a non-GUI-based application terminates.
If a catch handler throws an exception, the finally block still executes. Then the
exception is passed up the call chain for a calling method to catch and handle. The
catch block may be omitted when thefinally clause is used.
Throw Statement
It is possible that the catch handler that catches an exception may decide it
cannot process the exception, or it may want to let some other catch handler handle
the exception. In this case, the handler that received the exception can rethrow the
exception with the statement:
throwexceptionReference;
whereexceptionReferenceis the parameter name for the exception in the catch handler.
Such a throw rethrows the exception to the next enclosing try block.
Even if a handler can process an exception, and regardless of whether it does any
processing on that exception, the handler still can rethrow the exception for further
processing outside the handler. A rethrown exception is detected by the next enclosing
try block and is handled by an exception handler listed after that enclosing try block.
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A throws clause lists the exceptions that can be thrown by a method as in
intfunctionName( parameterList)
throwsExceptionType1, ExceptionType2, ExceptionType3, …
{
// method body
}
The types of exceptions that are thrown by a method are specified in the method
definition with a comma-separated list in the throws clause. A method can throw
objects of the indicated classes, or it can throw objects of their subclasses.
Some exceptions can occur at any point during the execution of the program.
Many of these exceptions can be avoided by coding properly. These are run-time
exceptions, and they derive from class RuntimeException. For example, if your
program attempts to access an out-of-range array subscript, an exception of type
ArrayIndexOutOf-BoundsException(derived from RuntimeException) occurs. Your
program clearly can avoid such a problem; hence, it is a run-time exception.
Another run-time exception occurs when your program creates an object
reference, but has not yet created an object and assigned it to the reference. Attempting
to use such a null reference causes a NullPointerExceptionto be thrown. Clearly, your
program can avoid this circumstance; hence, it is a run-time exception. Another run-
time exception is an invalid cast, which throws a ClassCastException.
Writing Own Exception Handler
In Java programming language we can write own exception handler. Sometimes
weneed our own exception handler to handle some type exception. To make own
exception handler we need inherit some class Exception.
This is example to writing own Exception Handler
// make NegativeNumberException
classNegativeNumberException extends Exception {
// No Code here
}
classDemoCreateException{
public static void main(String[] args){
//Example for using NegativeNumberException
try{
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// We throw negative number exception
throw new NegativeNumberException();
}catch(NegativeNumberExceptionnne){
System.out.println(“Error in Negative Number”);
}
}
}
This is simple own exception handler. In the example above we not define any
code in the class handler. We can add constructor and method to describe exception that
we handle too.
More on Exception Handling
The class names Error, Exception, and RuntimeException are somewhat
confusing. All three of these classes are exception, and all of the errors discussed here
occur at runtime. The exception classes can be classified into three major types: system
errors, exceptions, and runtime exceptions.
System errors are thrown by the JVM and represented in the Error class. The
Error class describes internal system errors. Such errors rarely occur. If one does,
there is little you can do beyond notifying the user and trying to terminate the
program gracefully. Example,LinkageError: a class has some dependency on
another class, but the latter class has changed incompability after the compilation of
the former class; and VirtualMachineError: the JVM is broken or has run out of the
resources it needs in order to continue operating.
Exceptions are represented in the Exception class, which describes errors caused
by your program and by external circumstances. These errors can be caught and
handled by your program. Example, ClassNotFoundException: attempt to use a
class that doesn’t exist; and IOException: related to input/output operations, such
as invalid input, reading past the end of a file, and opening a nonexistent file.
Runtime exceptionsare represented in the RuntimeException class, which
describes programming error, such as bad casting, accessing and out-of-bounds
array, and numeric errors. Runtime exceptions are generally thrown by the JVM.
Example, ArithmeticException: dividing an integer by zero;
NullPointerException: attempt to access an object thorugh a null reference
variable; IndexOutOfBoundsException: index to an array is out of range; and
IllegalArgumentException: a method is passed an argument that is illegal or
inappropriate.
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RuntimeException, Error, and their subclasses are know as unchecked
exceptions. All other exceptions are known as checked exceptions, meaning that the
compiler forces the programmer to check and deal with them.
1. Exercise
Please make a program to fill Guest Book
1. The program begins by asking for inputs:
- Name
Validate name’s length must be 5-15 characters!
- Age
Validate Age must be number between 17-50! (use Try-Catch concept)
- Comment
Validate that comment must be filled!
2. Print data from Guest Book.
Print Screen of the Program Ask User to input data
Print Screen of user wrong input
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Print Screen of Data GuestBook
a. Task 01 - Create Project Java in Eclipse
i. Run Eclipse from Start Menu
ii. Open Menu File -> New -> Project
iii. On Project Window, choose Java Project and click next
iv. Enter name of project,click next and finish
v. On tree panel on the left side window, expand Project folder
vi.Right click on src and create new class
vii. Enter the name class
viii. Then Press Finish
b. Task 02 – Make and validate inputs from user
First ,you must type import java.util.Scanner as library for class Scanner
Declare variable to save value and object from Scanner for receive input
Input name
In this section you must use do while to loop if user do wrong input.
Input Age
In this section you must use do while to loop if user do wrong input.
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Function in.nextLine() here is to get all buffer input from user like enter press.
Input Comment
In this section you must use do while to loop if user do wrong input.
c. Task 03 – Print Data Guest Book
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Chapter 07
Array
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Array Definition
Arrayisastructureddata typeasafixedamount(based on what isdefined)
andgivenaspecificname(as variable). In a simple word, an Array is a collection of items
which have same data type. An item in anArrayis called as elementsand
arrangedinrows.The position of an item in an array is defined by an index which
started from 0. Every arrayhas an addressadjacent/adjoiningdependentwidthdata
types.However, keep in mind,althoughits elementsarrangedinrows, the arraycan stillbe
accessedat randomin thememory.Arrayscan alsobe an array of1dimension, 2dimensions,
evenn-dimensional.
Illustration of one–dimensional array
Array Declaration and Manipulation
Arrayis declared like a variable. At the time of declaring arrays, you should make
a list of data types, followed by a pair of square brackets [], then followed by the
identifier name or you can place a pair of brackets [] after the identifier name also. In
declaring an Array, wemust allocatehow manyelementsthe array (usually we call it array
size) can holdbyusing the keyword ―new‖. For example:
// declare the data type, and identifier
int scores [];
// allocate how many elements on this array
scores = newint[100];
// this array can contain 100 elements
or it could be written with
// declaration and instantiate object
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int scores [] = newint[100];
// this variable can contain 100 elements
The value of array that we create using above code will contains its data type
default value, as for the example above, the int data type will have default value filled
with 0.
We can also directly assign the value for each element in our array, when we
declare the array, but the array size will be same as the total elements when we first
declare the array.
For Example:
int scores [] = {1,2,3,4,5,6,7,8,9,0};
Each element in the array above will be filled with the value that we assigned,
and the size of the array will be constant 10, because we declare this array with 10
elements.
We can also duplicate array like we assigning a value to a variable using other
variable, as an example:
int scores[] = {1,2,3,4,5,6,7,8,9,0};
//to duplicate array scores to scoresDuplicate
intscoresDuplicate [] = scores;
on the above code, the scoresDuplicate variable will be hold exactly same value as the
scores variable.
Beware, the statement doesn’t copy the contents of the array by scores to
scoresDuplicate, but merely copies the reference value from scores to
scoresDuplicate. The array previously referenced by scoresDuplicate is no longer
referenced; it becomes garbage, which will be automatically collected by the JVM.
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In Java, you can use assignment statements to copy primitive data type
variables, but not arrays. Assigning one array variable to another array variable actually
copies one reference to another and makes both variable point to the same memory
location. Thus, changing value of scores will change value of scoresDuplicate, too.
There are three ways to copy arrays:
Use a loop to copy individual elements one by one
for(inti=0; i<scores.length; i++)
scoresDuplicate[i] = scores[i];
Use the static arraycopy method in the System class
System.arraycopy(scores, 0, scoresDuplicate, 0, scores.length);
Use the clone method to copy arrays
scoresDuplicate = scores.clone();
To getthe length (or usually called by size)ofanarraywecanuse the.length after
the array name.
For Example:
int scores[] = {1,2,3,4,5,6,7,8,9,0};
int size = scores.length;
System.out.println(size);
Output:
Before the assignment intscoresDuplicate [] = scores;
scores scoresDuplicate
1,2,3,4,5,
6,7,8,9,0
?
After the assignment intscoresDuplicate [] = scores;
scores scoresDuplicate
1,2,3,4,5,
6,7,8,9,0
?
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To access the item inside array, we must define the item position (or usually
called index) we want to access. We can add, remove or change the item inside an array
like a single value variable.
int scores[] = newint[20];
scores[0] = 17;
scores[1] = 7;
scores[2] = 10;
scores[3] = 5;
System.out.println("The First Scores: "+scores[0]);
System.out.println("The Second Scores: "+scores[1]);
System.out.println("The Third Scores: "+scores[2]);
System.out.println("The Fourth Scores: "+scores[3]);
Output:
In the example above, we’re assigning a value into scores array, 17 to index 0, 7
to the index 1, and so on. After that we will try to get the value from each index and
print it on the console window.
To print all item on the array, we can loop the array that we declared before, we
can use foreach or the common for loop. For Example:
System.out.println("this is foreach to display the content of array
scores: ");
// for-each loop
for(intvalue:scores)
{
System.out.print(value+", ");
}
System.out.println("\nthis is the common for to display the content of
array scores: ");
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// for-loop
for(inti = 0;i <scores.length;i++)
{
System.out.print(scores[i]+", ");
}
Explanation:
In this statement, we can use foreach or the common for.
for(intvalue:scores)
In this statement, int value is used to accommodate the value of each index in
the array scores. The index is starting from 0 until n, where n is thearray length of
variable scores and the index will increase when turning to the initial statement for
itself.
System.out.print(value+", ");
This statement will display the value of the contents of the array variable
starts from 0 to length of the array.
for(inti = 0;i<scores.length;i++)
This statement is the common for inti is used for the initial value of a loop, then
i<scores.length here used for the initial loop, which means it will be repeated as much
as the length of an array, then the i++ means that the increment in each iteration is for
variable i.
System.out.print(scores[i]+", ");
This statement will display the value of the contents of the array variable
starts from 0 to length of the array.
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Output:
Two Dimentional Array
Two dimentional array means, for every element in an array variable, also
contains an array object, something like array inside of array. The size of the array is
not always same, and can be different. The dimention for array can be more than two
dimention, it depends on our needs.
Declaration of Two Dimentional Array:
int scores[][];
scores = newint [3][4];
scores[0][0] = 5;
scores[0][1] = 20;
scores[0][2] = 1;
scores[0][3] = 11;
scores[1][0] = 4;
scores[1][1] = 7;
scores[1][2] = 67;
scores[1][3] = -9;
scores[2][0] = 9;
scores[2][1] = 0;
scores[2][2] = 45;
scores[2][3] = 3;
or
int scores[][] = {{5,20,1,11},{4,7,67,-9},{9,0,45,3}};
Ilustration of 2 dimentional array above
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We can also loop the two dimentional array like what we do in one dimentional
array, with a little modification to our code. For Example:
publicclass Main {
publicstaticvoid main(String [] args)
{
System.out.println("this is foreach to display the content
of array scores: ");
for(int value[]:scores)
{
for(int value2 : value)
{
System.out.print(value2+" ");
}
System.out.println();
}
System.out.println("\nthis is the common for to display
the content of array scores: ");
for(inti = 0;i < 3;i++)
{
System.out.print(i+" -> ");
for(int j = 0; j < 4;j++)
{
System.out.print(scores[i][j]+" ");
}
System.out.println("");
}
}
}
Explanation:
In this statement, we can use foreach or the common for.
for(int value[]:scores)
In this statement, int value[] is used to accommodate the value of each index in
the array two dimensional scores. The index is starting from 0 until n, where n is
thearray length of variable scores and the index will increase when turning to the initial
statement for itself.
for(intvalue2:value)
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In this statement, int value2 is used to accommodate the value of each index in
the array value. The index is starting from 0 until n, where n is thearray length of
variable value and the index will increase when turning to the initial statement for itself.
System.out.print(value2+" ");
This statement will display the value of the contents of the array variable starts
from 0 to length of the array and add a space character after each item.
for(inti = 0;i< 3;i++)
This statement is the common for inti is used for the initial value of a loop, then
i< 3 here used for the initial loop, which here means it will be repeated as much as the
length of an array, then the i++ means that the increment in each iteration is for
variable i.
for(int j = 0;j < 4;j++)
This statement is the common for and the second for in this loop sequence. int j
is used for the initial value of a loop, then j < 4 here used for the initial loop, which here
means it will be repeated as much as the length of the inner array, then the j++ means
that the increment in each iteration is for variable j.
System.out.print(scores[i][j]+" ");
This statement will display the value of the itemsin the array scores
starts from 0 until the length of the array in two dimensional, i for the first array
(scores[i][xxx]) and j for the second array (scores[xxx][j]).
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Output:
Ragged Arrays
Each row in a two-dimensional array is itself an array. Thus the rows can have
different lengths. An array of this kind is known as a ragged array. Here is an example
of creating a ragged array.
If you don’t know the values in a ragged array in advance, but know the sizes,
say the same as before, you can create a ragged array using the syntax that follows:
int[][] triangleArray = new int[5][];
triangeArray[0] = new int[5];
triangeArray[1] = new int[4];
triangeArray[2] = new int[3];
triangeArray[3] = new int[2];
triangeArray[4] = new int[1];
The syntax new int[5][] for creating an array requires the first index to be specified.
The syntax new int[][] would be wrong.
Int [][] triangleArray = {
{1, 2, 3, 4, 5},
{2, 3, 4, 5},
{3, 4, 5},
{4, 5},
{5}
};
1 2 3 4 5
2 3 4 5
3 4 5
4 5
5
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1. Exercise
For exercise, we will make a simple program. This program is a book store where
the user can add books to shoping cart and in the end of the transaction, the user can
buy all of the book he/she add to shoping cart. There are some list of books the user can
buy and 3 menus in this program.
There are:
1. Add to Shopping Cart
2. See Shopping Cart
3. Exit and Pay
- If the User choose Add to Shopping Cart, then:
o The user were asked to choose which book they want to buy, validate the
user input is only 1 until 5.
o After this, the user were asked to input the quantity of the book, validate
the user just can input 1 until the available book stock.
o Then, display the information of the book that user want to buy.
o If the existing stock is zero, the user can‟t buy that book, and the
program will display error message: ―The Book is no stock‖.
- If the User choose See Shopping Cart, then:
o Show all the books the user want to buy, and it’s name, quantity the user
want, total price of that books, and the grand total.
o If the user still not buy anything, the program will show error message:
―Please add book to shopping cart first‖
- If the User choose Exit and Pay, then:
o Show the grand total of the transaction and ask the user to input the
payment. Validate the payment cannot be lower than grand total.
o If the payment has change, show the change of the payment.
o The program will end.
a. Task 1: Create Project Java in Eclipse
- Run Eclipse from start Menu
- Open Menu File New Project
- Choose Java Project Fill Project Name example: ―Answer07‖
- Press Finish, and show pop up, choose ―No‖
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b. Task 2: Create the main Class
The Main class is the primary class of our program that will be invoked first by
the compiler. And the main method will call the constructor of main class where we put
our code to make this program, and we also import java.util.Scanner to use the
Scanner class.
c. Task 3: Create variable arrays
First, we must decide how many arrays will be used. In this program we need
name, price, quantity, quantity the user want to buy and total price in for each book. So,
we make 5 arrays to store the required data above, with different name and of course
we must give it a name with characteristic and describe it’s function.
We will also make a object of Scanner class, and make variable that needed in
our program like in the code below.
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d. Task 4: Create main menu
After we create all the object, array and variables we need, we will create main
menu for our program, see the code below.
Explanation:
This part of code used to print all available book to sell, the logic is to print all the
data on the corresponding arrays, so we use for loop to print all data in the array
starting from index 0 until the length of the array, and to print the data, we will use
printf to print the data using our defined format.
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This code used to validate the user input must be between 1 and 3, and we will
surround the input statement with try-catch block to catch if there is any exception
occurred if the user input is not a number.
This code used to validate if the user input isn’t 3, then the program will loop
from the beginning until the user input 3. And if the user input 3, then the program will
be ended.
e. Task 5: Build menu number one (Add to Shopping Cart)
Before we build menu 1, we must make selection to put code menu one, two and
three. In this program, we will a use switch case structure.
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After we make switch case, we can put code for menu 1 in case 1.
Explanation:
In this code, we stored input from the user to variable qtyTemp to add qty from
the product that user want to buy.
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We display the product that user want to buy with the product name, quantity
and total price to be added to shopping cart.
In this code, we will add how many quantity we want to buy to the array. As we
know, the index of a array started from 0, but if the user want to buy the first item, they
will input a number ―1‖, so we will decrease the user input by 1.
After that, we will add the quantity of the book the user want to buy (qtyTemp)
to the array qtyCart (qtyCart + qtyTemp), and we must decrease the book quantity
from array qty as many as the user buy (qty - qtyTemp).
For the price, we will multiply the book price, with the quantity of the book that
user want.
For computing grand total of the price,first, we set the variable grand to 0. So
with looping for, we loop 5 times or according to the length of priceCart, and we add a
value to grandwith every price on the priceCart array.
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f. Task 6: Build menu number two (see Shopping Cart)
We put the code for menu number two in case 2.
Explanation:
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We will loop 5 times or as many as the length of arrays name and in this loop, we
validate, if the quantity in the shopping cart on index i is more than 0, we set the
variable flag value to 0 and we break the loop, because it means the user is already buy
some item, or if it less than zero (the user never buy any item), we set the variable flag
value to 1 and we continue the loop until the loop ends or we find the break statement.
After we validate the quantity, we will validate the flag, if it’s 0, meaning one of
item quantity the user want to buy is more than 0. So we use the loop to display
products in shopping cart. But before we display, we make a validation again, if the
quantity in shopping cart we want to display is more than 0 or not. If it yes, we display,
if not, we do not display the product. After that we display grandin the end and we
already out in loop. And if the flag is not 0, we ask the user to add a product to
shopping cart first.
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g. Task 7: Build menu number three (Exit and Pay)
We put the code for menu number three in case 3.
Explanation:
In this code, first we will validate, is the grand total is more than 0 or not, if it is
not, we didn’t display the grand total and other data, but if the grand total is more than
0, we will display the grand total, and we ask the user to input their payment, and we
will validate the money must be more than or equals the grand total. If the money is
more than grand total, we will calculate the change for their payment. And the program
will be ended.
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Chapter 08
Methods
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Method Definition
The aim of method or function is to group the commands that are designated to
conduct a larger order. The main things needed in the making and declaring a method
are:
1. Modifiers - permissions that would regulate access this method, will
be discussedbelow.
2. Return value– data type to be returned by this method, void when no value is
returned.
3. Method Name -name to the method or function. This must be following a naming
convention.
4. Parameter-the declared type of data to get sent value as input for the
method.Surrounded by parentheses, (). A method can have no parameterat all.
5. The content of method-the commands to be run in the method,surrounded by {}.
One example that will be commonlyused is the main method:
public static void main(String [] args){ //content }
Explanation:
1. public static are the modifiers
2. void is the return value, in this case the method does not return a value
3. main is the method name
4. String [] args is the parameter to get sent value, in this case is an array of String
5. {/ / content} is where to put the commands to be run.
Example of declaringa method that we want to create:
publicstaticvoid function1(/*parameters*/int value)
{
//content
System.out.println("The Value is "+value);
}
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Example of calling a method that we have created:
public static void main(String[] args) {
int score = 10;
function1(score);
}
Explanation:
function1(score) is used to call the function1method with their parameters if
available. So, if we call this method, the code inside the method will be executed.The
statement System.out.println("The Value is "+value);will be executed.
Variable Scope
In Java, there are 2 kinds of variable scope; there are global variable and local
variable. If we use global variable, every method can access this variable and can
change its value. But if we use local variable, it is just recognized in that method.We
can’t use it in other methods except we send (pass) that variable to another method.
Global Variable
public class Example
{
staticintnumber;
publicstaticvoid function()
{
number = 10;
System.out.println("The Value in Global: "+number);
}
publicstaticvoid main(String[] args) {
function();
}
}
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Explanation:
Variable number, as a global variable, can be used in every method.We declare
variable number as a global variable and use it in method function. We fill number
with 10, and display the numbervalue. In the main method, we will call the method
function() to see the output.
Output:
Local Variable
public class Example
{
publicstaticvoid function()
{
intnumber = 10;
System.out.println("variable value in function: "+number);
}
publicstaticvoid main(String[] args) {
intnumber = 17;
function();
System.out.println("variable value in main: "+number);
}
}
Explanation:
The variable number, as a local variable, was declared inside the method
function().So, its value in method function() and method main()are different.The
two variablesnumber were declared on the separated method.
Output:
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Passing Parameter to a Method
We can send a value to a method to be processed.The value that will be passed
between method is called as a parameter.The parameter can be a variable, array, even
an object. There are 2 ways to pass a parameter:Passing by Value and Passing by
Reference.
Passing Parameter by Value:
publicstaticvoiddisplayParam(intparams)
{
System.out.println("The Paramater Value: "+params);
}
publicstaticvoid main(String[] args)
{
intval = 7;
method(val);
}
Explanation:
Passing parameter by value means that the parameter passed only its value, not
the address or reference.We can’t change the variable val value in
displayParammethod, because we just pass its value, not its reference.
Output:
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Passing paramater by reference:
publicstaticvoid method(int values[])
{
values[0] = 7;
}
publicstaticvoid main(String[] args) {
int scores[] = newint [5];
scores[0] = 15;
System.out.println("The value before change:"+scores[0]);
method(scores);
System.out.println("The Value after change: "+scores[0]);
}
Explanation:
In this section, we will try to passparameter by reference.We don’t pass the value
of the variable, but the reference to that variable.
Every variable has a address or reference.If we pass it to a method, we pass
everything in that variable: the address and the value. We can change the variable value
in that method.The value on the sender method is also changed.
For a example, we have an array scores in main method.Why we use array?
Because in Java, we can pass reference by using array variable. In scores[0], first we
instantiate with 15 and we display it.Then we call method(scores).In method(), the
scores[0]is changed to 7, and then we display the value in the main() method.The
value on the main method is also changed.
Output:
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Return Value
There are method returning a value and no returning anything (null). Amethod
that returnsnulluses the keyword “void” for the return type.It meansthat the method
doesn’t return any value like this code:
publicstaticvoid method(int values[]){
values[0] = 7;
}
The other one is method which returns a value.We must define the return type
for the method.Return type can be a primitive data type, an array or a Class. The return
type for the method must be same with the data type of the returned value by the
method. This method must use keyword return to return a value. Let’s see the example
below:
public static intaddValue(intvalue1, intvalue2)
{
returnvalue1+ value2;
}
public static void main(String[] args) {
intresult = addValue(5, 7);
System.out.println("The Result 5 + 7 :" + result);
}
Explanation:
In the main method, we call method addValue(5, 7).The method addValue()
will returning a value, so we will store the result on the variable result.As we can see,
we didn’t use keyword voidwhen declaring the method addValue(), but we use
keyword int.Why we use int? It depends on what type we want to return. If we want to
return int, so we use int.If we want to return a floating number, so we use float. In
method addValue(), we will add value1 and value2, and finally we return the result of
the addition. The result variable is used to store the value that is returned by the
method addValue().
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Output:
In a different case, a method can return an array.We use keyword int[] to
return an array of int. Example:
public static int[] givingArray()
{
intdecimal[] = {45,12,53,34,25,16,77};
returndecimal;
}
public static void main(String[] args) {
intresult[] = givingArray();
for(inti = 0;i<result.length;i++)
{
System.out.println((i+1)+"->"+ result[i]);
}
}
Explanation:
In main method, we called givingArray().Everything that is returned by
givingArray()will be stored on array result.The method givingArray()must be
returning an array. We use keyword int[] to return an array of int. In givingArray(),
we declare a new array with initialization and we return the array to main method.Array
result will have the same items with the array that is returned by givingArray().
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Output:
Overloading Method
We can make two methods with a same name. Sometimes, we need methods
with same function, and only differ in parameter, Java allow us to have this kind of
method: two or more methods with same name, but with different parameter.The
parameter can be differed on the data type, and number of parameters. This kind of
method is called as Overloading Method. Example:
public static void view(String word)
{
System.out.println("The Word is: "+word);
}
public static void view(String word, String word2)
{
System.out.print("The First Word is: "+word);
System.out.println(" and the second Word is "+word2);
}
public static void main(String[] args) {
view("Hallo");
view("Hallo","World");
}
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Explanation:
We write 2 methods with the same name but different paramater. It’s called
overloading method. It isn’t an error.Both methodsare different function. In main
method, we can call both methods.We call the first method with one parameter and the
second method with two parameters.
Output:
Each time a method is invoked, the system stores parameters and variables in an
area of memory known as a stack, which stores elements in last-in, first-out fashion.
When a method calls another method, the caller’s stack space is kept intact, and new
space is created to handle the new method call. When a method finishes its work and
return to its caller, its associated space is released.
Passing Arrays to Methods and Returning an Array from a Method
Just as you can pass primitve type values to methods, you can also pass arrays
to methods. For example, the following method displays the elements in an array of int:
public static void printArray(int[] array) {
for(inti=0;i<array.length;i++){
System.out.println((array[i]+" ");
}
}
You can invoke it by passing an array. For example, the following statement invokes the
printArray method to display 3, 1, 2, 6, 4, and 2.
printArray(new int[] { 3, 1, 2, 6, 4, 2 });
There’s no explicit reference variable for the array. Such array is called an anonymous
array.
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A method may also return an array. For example, the method shown below
returns an array that is the reversal of another array:
public static int[]reverse(int[] list) {
int[] result = new int[list.length];
for(inti=0, j=result.length-1; i<list.length; i++, j--) {
result[j] = list[i];
}
}
1. Exercise
For exercise, you’ll creat a program to calculate everything that user inputs. First,
this program will ask a user to input how many number that the user want to
calculate.Input must be validated between 2 and 6.Afterthat,the program will ask
the user to input nnumbers according to the previous input.If on the previous, the user
inputs 4, the user will be asked to input 4 numbers later.Validate the next input must
be between 1and 25. The program will display 3 menus:
1. Calculate the All numbers
This menu displays the addition of all inputted number
2. Average of the All number
This menu displays the average of all inputted number
3. Exit
End of program.
a. Task 1: Create Project Java in Eclipse
- Run Eclipse from start Menu
- Open Menu File New Project
- Choose Java Project Fill Project Name example: ―Answer08‖
- Press Finish, and show pop up, choose ―No‖.
b. Task 2: Create the main Class
The Main class is where we write code. We write main method in the Main class,
and also import java.util.Scanner to use the Scanner class.
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We need a global variable to create a Scannerobject, so it can be used by every
method.
c. Task 3: Create the input for calculating
Application needs to ask user to input a number, and also input nnumber.
We must write a method to input the number onint [] amount =
inputAmount();.Method inputAmountmust return an array.
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We use keyword int[], not int or void, because the method returns array of
int.At the end of method,it returns array of int whose length that has been inputted by
the user.
d. Task 4: Create the main menu method
After we create the first step of this program, we create a method to display the
menu.
Method cls()is used to make a new clear window of command
prompt.MethoddisplayNumber(amount) is used to display the number that had been
inputted by the user.Methodmenu() is used to display the menu and returned the user’s
choice.
The code validateswhether the input is 3 or not. It will loop until the user input 3.
This is the code of the methods:
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e. Task 5: Create the menu contents
Before we create menu 1, we must make a selection process. We may use
switch case.
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Afterthat, we write code for each menu in each case.
Menu 1 isused to display calculating process of all numbers.
StatementSystem.out.println("Calculate the All number is
"+calculate(amount)) means that the method calculatehas paramater of array and
return a value. Here’s the method calcuate.
We just use loop process to count variable ifrom 0 until the length of the array
amount, and we sum its value to variablecount. Afterthat, we return count.
Menu 2 is used to display the average of all numbers.
StatementSystem.out.println(" Average of the All Number is
"+average(amount));means that the method averagehas parameter of array and
return a value. Here’s the method average.
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This method returnsa result of calculate(amount) divided by length of array.
This method also call method calculate.
Menu 3 is used to display some messages and finish the program.
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Chapter 09
Recursion
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Recursion Definition
Recursion is a method that directly or indirectly invokes themselves. It means
thata method with name ―function1‖ calls itself.Recursionwill be neededin a program
which has a ―Divide and Conquer”characteristic.The declaration of recursion is same with
usual method.Remember, we must make a parameter or global variable to use a
condition to exit the function (which usually called as base-caseor stopping condition).If
not, the function will call itself infinitely and the runtime stack overflowsexception may
occur.
Example:
publicstaticvoid function1(int value)
{
if(value > 0)
{
System.out.println("Recursive");
function1(value-1);// we call the function itself
}
}
publicstaticvoid main(String[] args) {
function1(3);
}
Explanation:
In function1, we have a parametervalue. In this method, if value more than
zero,it will display the word ―Recursive‖ and call the function with parametervalue-1. In
main method, it call function1 with value 3.
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Themain method will call function1(3). In function1method itself, it will create
its base-case (when the recursion will end) to check whether the variable valueis more
than 0 or not. If it’s true, the program will display ―Recusive‖ and call function1(3-1) or
in a simple form, function1(2), and so on until its value less than or equals 0 so the
function1 ends.The output will display ―Recursive‖ 3 times.
Output:
When we learn about recursion for the first time, we usually compare a recursion
with the common looping. The idea of iteration is similar to recursion looks like this:
publicstaticvoid main(String[] args) {
for(inti = 0; i< 3; i++)
{
System.out.println("Recursive");
}
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}
The output of the loop above is same with the recursion we’ve made with function1().
We can also return a value in a recursion when we need it.For example:
publicstaticint function1(int value)
{
if(value > 0)
{
return value+function1(value-1);
}
return value;
}
publicstaticvoid main(String[] args) {
System.out.println(function1(3));
}
Explanation:
The explanation of this code is exactly same with the recursion without return
value.The different is, in the example above, when we callfunction1(3), we check
whether the value is more than 0 or not.
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If it’s true, then it will return value+function1(3-1) or function1(2) and so
on. In that case, we must call the function1(2) on go until the value is 0 so we call
function1(0).If the condition is false, it returns the value without calling the method
again.So,it returnsa value and function1(0)ends.The chainsare:
function1(0): return 0, the function1(0) end;
function1(1): return 1+function1(0) return 1, the function1(1) end;
function1(2): return 2 + function1(1) return 3, the function1(2) end;
function1(3): return 3+function1(2) return 6, the function1(3) end;
and we will back to main method.
Output:
The recursionmethod is similar with loop process:
publicstaticvoid main(String[] args) {
intvalue = 0;
for(inti = 0; i<= 3; i++)
{
value+=i;
}
System.out.println(value);
}
Recursion is an alternative form of program control. It is essentially repetition
without a loop. When you use loops, you specify a loop body. The repetition of the loop
body is controlled by the loop control structure. In recursion, the method itself is called
repeatedly. Recursion bears substantial overhead. Each time the program calls a
method, the system must assign space for all of the method’s local variable and
parameters. This can consume considerable memory and requires extra time to manage
the additional space.
Any problem that can be solved recursively can be solved nonrecursively with
iterations. Recursion has some negative aspects: it uses up to much time and memory.
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Why, then, should you use it? In some cases, using recursion enables you to specify for
an inherently recursive problem a clear, simple solution that would otherwise be difficult
to obtain.
The decision whether to use recursion or iteration should be based on the nature
of, and your understanding of, the problem you are trying to solve. The rule of thumb is
to use whichever approach can best develop an intuitive solution that naturally mirrors
the problem. If an iterative solution is obvious, use it.
Your recursive program could run out of memory, causing a
StackOverflowError. If you are concerned about your progam’s performance, avoid
using recursion, because it takes more time and consumes more memory than iteration.
2. Exercise
You have to make a program that uses binary number, Fibonacci number,
and odds and even number.First, you are asked to display menu:
1. Binary Number
2. Fibonacci Number
3. Odd and Even Number
4. Exit
- If user chooses Binary number, then:
o User is asked to input a number that user want to convert to binary
number.Validate the number so just can input number from 1 until
255.
o After this, display the binary number of it.
- If user choosesFibonacci number,then:
o User is asked to input a number and display nFibonaccinumber.Validate the
number so just can input number from 1 until 20.
o After this, display the nFibonacci number, where n is user’s input.
- If user choosesOdd and Even Number,then:
o User is asked to input a number and display nodd and even number.Validate
the number so just can input number from 5 until 50.
o After this, user is asked to input a start-number, validate the number so
just can input from 1 until 100.
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o After this, display Odd and Even Number as many as user’s input beginsfrom
the start-number.
- If the user choosesExit, the program ends.
a. Task 1: Create Project Java in Eclipse
- Run Eclipse from start Menu
- Open Menu File New Project
- Choose Java Project Fill Project Name, example: ―Answer09‖
- Press Finish, and show pop up, choose ―No‖.
b. Task 2: Create the main Class
The Main class is where we write code. We will make the main method where
we will write code in the Main class, and also import java.util.Scanner to use the
Scanner class.
In this case, we use a global variable to create the scanner object, so it can be
used by every method.
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c. Task 3:Create the main menu method
First, create the menu:
In this code, cls() isused to make a simulationof cleared command prompt.The
statementchoice = menu() isused to display the menu and get user’s choice.
The codeis used to validate whether the input is 4 or not (it will loop until the
user input 4). If the user input 4, the program will be ended.
This is the code of the methods:
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d. Task 4: Create the menu contents
Before we create menu 1, we make a selection process.We use switch case.
Afterthat, we write code for each menu in each case.
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Explanation:
In case 1, first we ask the user to input decimal number and validate the
number must be between 1 and 255. We use method validate(), with 3 parameters, to
display some word, minimum and maximum input number. Afterthat, we call
methodtoBinary(number) to convert decimal number to binary number.
Method validate that is used in case 1, 2 and 3:
In this method, we display the word that we have passed. We get user’s input
and store to variable number. We validate the number with min and maxthose we’ve
passed. Afterthat, we return the number.
Method toBinary to convert decimal to binary number:
It has base-case to stop the method if the number equals to 0.If the number
doesn’t equalto 0, it call the method withindivided-by-two parameter. After the number
is 0, it will display the number modulus by 2.
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Example: The decimal number is 10, then the recursion steps:
o toBinary(10)
o Number != 0 -> toBinary(5) number = 10 …(1)
o Number != 0 -> toBinary(2) number = 5 …(2)
o Number != 0 -> toBinary(1) number = 2 …(3)
o Number != 0 toBinary(0) number = 1 …(4)
o Number == 0 end of function toBinary(0)
o Back to number(4), display number%2 1%2 = 1
o Back to number(3), display number%2 2%2 = 0
o Back to number(2), display number%2 5%2 = 1
o Back to number(1), display number%2 10%2 = 0
o The result is 1010
Incase 2, we ask the user to input the number, and validate the number
between 1 until 20. We use the method validate, with 3 parameters, to display some
word, minimum input number, and maximum input number. Afterthat, we call method
toFibonaci(number,0,1).It’s used to displayFibonacci number as many as passed
number.
We use method toFibonaci()to displaythe fibonacci number:
In this method, it has base-case to stop if the number equals to 0.If the number
doesn’t equals to 0, we display the value2. Afterthat, wecall the method again with
parameter number-1,value2, and value1+value2. The algorithm of fibonacci is:
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Fibo(n) = Fibo(n – 1) + Fibo (n – 2)
Example:Input = 5, so the steps are:
o toFibonaci(5,0,1)
o Number != 0 -> display ―1 ‖ call toFibonaci(4,1,1)
o Number != 0 -> display ―1 ‖ call toFibonaci(3,1,2)
o Number != 0 -> display ―2 ‖ call toFibonaci(2,2,3)
o Number != 0 -> display ―3 ‖ call toFibonaci(1,3,5)
o Number != 0 -> display ―5 ‖ call toFibonaci(0,5,8)
o Number == 0 end of function toFibonaci(0,5,8)
o Number == 0 end of function toFibonaci(1,3,5)
o Number == 0 end of function toFibonaci(2,2,3)
o Number == 0 end of function toFibonaci(3,1,2)
o Number == 0 end of function toFibonaci(4,1,1)
o The result is ―1 1 2 3 5 ‖
In case 3, weask user to input amount of number to be displayed.We validate
the number between 5 until 50, and then ask the user to input the initial number of odd
and even number to be printed.
Afterthat,we validate the input must be between from 1 until 100. In this code,
we use the method validate()with 3 parameters, to display some word to, minimum
and maximum inputted number.
We call function toOdd(number, start) to display odd numberand start based
on thepassednumber.We call function toEven(number, start) to display number even
and start based on passed number.
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In both methods, it has base-case to stop if the number equals 0.Themethod
toOdd() and toEven()are nearly same.The different ismethod
toOdd()validateswhether if the start number modulus by 2 is 0 and increase it by 1
(because we want to display the odd number).
Example: We have number 4 and it starts in 5
o toOdd(4,5)
o Number != 0 -> start%2 != 0 display ―5 ‖ call toOdd(3,7)
o Number != 0 -> start%2 != 0 display ―7 ‖ call toOdd(2,9)
o Number != 0 -> start%2 != 0 display ―9 ‖ call toOdd(1,11)
o Number != 0 -> start%2 != 0 display ―11 ‖ call toOdd(0,13)
o Number == 0 end of methodtoOdd(0,13)
o Number == 0 end of methodtoOdd(1,11)
o Number == 0 end of method toOdd(2,9)
o Number == 0 end of method toOdd(3,7)
o Number == 0 end of method toOdd(4,5)
o The result is ―5 7 9 11 ‖
o toEven(4,5)
o Number != 0 -> start%2 == 1 start+1 display ―6 ‖ call toEven (3,6)
o Number != 0 -> start%2 != 0 display ―8 ‖ call toEven (2,8)
o Number != 0 -> start%2 != 0 display ―10 ‖ call toEven(1,10)
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o Number != 0 -> start%2 != 0 display ―12 ‖ call toEven (0,12)
o Number == 0 end of method toEven (0,12)
o Number == 0 end of method toEven(1,10)
o Number == 0 end of method toEven (2,8)
o Number == 0 end of method toEven (3,6)
o Number == 0 end of method toEven (4,5)
o The result is ―6 8 10 12 ‖
In case 4, it just display a sentence and finish the program.
The recursive implementation of the Fibonacci method is very simple and
straightforward, but not efficient. The more efficient solution is using loops. Though it is
not practical, the recursive Fibonacci method is a good example of how to write
recursvie methods.
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Chapter 10
Sorting
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Sorting Definition
In some application, sometimes we need to sort any of records. In that case, we can use
sorting algorithm. Sorting is a classic subject in computer science. We study sorting
algorithms to illustrate many creative approaches to problem solving, and these approaches
can be applied to solve other problems. Sorting algorithms are good for practicing
fundamental programming techniques using selection statements, loops, methods, and arrays.
In Java, we have so many sorting algorithms.In this tutorial, we will try to use 4 kinds of
sorting algorithm. There are bubble sort, selection sort, insertion sort, and merge sort.
Bubble Sort
public static void bubbleSort(int [] arr, int n)
{
for (int i = 0; i< n; i++) {
for (int j = n-1; j >i; j--) {
if(arr[j-1] >arr[j])
{
int swap = arr[j-1];
arr[j-1] = arr[j];
arr[j] = swap;
}
}
}
}
Explanation:
In Bubble sort, we need a loop according to how many records we have in the variable.So we
will use loop, start from 0 until n times.In this example, we will make a method called
bubbleSort() for an easier usage.
After we create a loop torepeat n times, we use for again to check the value in array
arr.In this case, we check from the last index of the array.If we find the value in the array on
index j-1is greater than index j, we must swap the both value.The idea behind bubble sort
algorithm is, if we find the lower value, we must put the value in front index.
So we will start comparing from the last index with the previous index.If the value on the
last index is smaller than the previous index, swap the value. This process will be looped
until we compare to the first index of the array (index 0).
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Selection Sort
public static void selectionSort(int [] arr, int n)
{
int temp;
for (int i = 0; i< n-1; i++) {
temp = i;
for (int j = i+1; j < n; j++)
if(arr[j] <arr[temp])
temp = j;
if(temp != i){
int swap = arr[i];
arr[i] = arr[temp];
arr[temp] = swap;
}
}
}
Explanation:
Selection Sort algorithm is similar to Bubble Sort algorithm.In Selection Sort, we will
search for the maximum or minimum value from the array, start from the first or last index of
the array until the end.Unlikely with the bubble sort, when we find the minimum or
maximum value, we will not swap the value, we just save the index in variable temp.
After we check the value using a loop, we will check whether the index we found on the
variable tempis same or not with the i, then we will swap the value.
Insertion Sort
public static void insertionSort(int [] arr, int n)
{
int i, j, temp;
for (i = 1; i<= n; i++) {
temp = arr[i];
for (j = i-1; j >= 0 &&arr[j] > temp; j--)
arr[j+1] = arr[j];
arr[j+1] = temp;
}
}
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Explanation:
In Insertion Sort algorithm, we need a temporary variable to store the value of an array on
index i(we use a variable temp). On the second loop, we will start the loop using variable j.If
the initial value of j is i-1, we will check whether the value of the array on index j is larger
than temp or not.
If it’s true, value of the array on index j+1 will be changed with the value of array on
index j, and continuing the loop until j >= 0orarr[j] is bigger than temp. After the second
loop finished, the value of arr[j+1] will be filled with temp. The first loop will be repeated
until the condition is deal.
Merge Sort
public class Main {
public static void mergeSort(int array[],int lo, int n){
int low = lo;
int high = n;
if (low >= high) {
return;
}
int middle = (low + high) / 2;
mergeSort(array, low, middle);
mergeSort(array, middle + 1, high);
int end_low = middle;
int start_high = middle + 1;
while ((lo <= end_low) && (start_high<= high)) {
if (array[low] < array[start_high]) {
low++;
}
else {
int Temp = array[start_high];
for (int k = start_high- 1; k >= low; k--) {
array[k+1] = array[k];
}
array[low] = Temp;
low++;
end_low++;
start_high++;
}
}
}
}
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Explanation:
Merge sort splits the array values in halves recursively until each half has only
single element. Merge the two 1/2 values together and sort the values. Do the same steps
iteratively until the values are not sorted.
First, we validate whether if lowis more than highor not, then the method ends.This
validationis used in recursiveuntil reachthe base-case. After that, we must split the array. The
data are divided by 2 and patched in variable middle.
Next we do recursionand send parameter array as array, low as lo and middle as n. We
do the recursion until we find low >= highcondition. We call the method again and send
parameter array as array, low as middle+1, n as high. Then, we patch variable end_low as
middle, and start_high as middle+1.
Working with merge sort algorithm
Let’s say that we have an unsorted array A[0],A[1],A[2], ...,A[n-1], and A[n] as input.
The following steps are followed by merge sort algorithm to sort the values of an array.
Steps of Merge Sort: Say an unsorted array values are: 12, 9, 4, 99, 120, 1, 3, 10
Step1: Spliting the values of array and divide the values into two
Step2: Merge two values and sort the values
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Step3: Merge four values and sort the values
Step4: Merge n values and sort the values, n must be even number
3. Exercise
For exercise, you’ll have to make a book store program. User can add books and sort it.
There are list of books that user add, and 4 menus in this program.
There are:
1. Add Book
2. Sort Book ByNameAscending
3. Sort Book By Price Descending
4. Exit
- If user chooses Add Book, then:
o User is asked to input the name of book, validate inputwith length of stringis 3
until 25.
o After this, user is asked to input quantity, validate input is 1 until 25.
o After this, user is asked to input prices, validate user input is 1000 until 20000.
o Then, display the information of the book that user add.
- If user choosesSort book by Name Ascending, then:
o If there’s no book in the list, display the error message: “Please add book first.”
o Sort the book by name ascendingly, then display the result.
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- If user choosesSort book byPriceDescending, then:
o If there’s no book in the list, display the error message: “Please add book first.”
o Sort the book by pricedescendingly, then display the result.
- If user choosesExit, thenprogram ends.
4. Answer
a. Task 1: Create Project Java in Eclipse
- Run Eclipse from start Menu
- Open Menu File New Project
- Choose Java Project Fill Project Name example: “Answer09”
- Press Finish, and show pop up, choose “No”.
b. Task 2: Create the main Class
The Main class is where we write code. We will make the main method where we
will write code in the Main class, and also import java.util.Scanner to use the Scanner
class.
In this case, we use a global variable to create the scanner object, so it can be used
by every method.
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c. Task 3: Create the main menu method
First, create the menu:
In this code, cls() is used to make a simulation of cleared command prompt. The
statement choice = display(name,price,qty,n)is used to display the menu and get user’s
choice.
The codeis used to validate whether the input is 4 or not (it will loop until the user
input 4). If the user input 4, the program will be ended.
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This is the code of the methods:
d. Task 4: Create the menu contents
Before we create menu 1, we make a selection process.We use switch case.
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After that, we write code for each menu in each case.
In case 1, first we ask the user to input name of book, and we validate the input must
be between 3 until 25 characters. We ask user to input quantity and price, and validate
quantity must be between 1 and 25, and price must be between 1000 and 20000.
We use the method validate, with 3 paramaters: display a message to ask user,
minimum input number, and maximum input number. All of the inputsare
assigned/stored to variable array. Afterthat, we display the name, quantity, and price
that have been inputted.
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Method validate:
In case 2, we call the method sortName(name,qty,price,n).In this method, we use
bubble sort algorithms to sort the records.We must swap 3 variables of array:name, qty,
and price. We use methodswap with the parameter of an Object array, integer i and j.
Method sortName uses to sort records based on name ascendingly.
Method swap uses to exchange an object/value each other:
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In case 3, we call the method sortPrice(name,qty,price,n).In this method, we use
selection sort algorithm to sort the records.
Method sortPrice uses to sort records based on pricedescendingly.
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Chapter 11
Utility
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Random Number
In java, we can generate a random number with Class Random from
java.util.Random package.If we want to generate a random number from 1 to 10,
there are the steps to random numbers:
o First, we must import java.util.Random
o Second, we must create an object of class Random, then we can use the object to
generate a random number.
o Third, we can store to intvariable or directly display to console.
importjava.util.Random;
publicclass Main {
publicstaticvoid main(String[] args) {
Random rand = newRandom();
System.out.println(rand.nextInt());
}
}
Output:
In that case, we just generate an uncontrolled random number.If we want to
generate a control random number, we must put a parameter inside rand.nextInt().
For example, if we put 5, the result will be between 0 until 4. If we want to generate a
random number between 1 until 10, we must put 10 and the result of random must be
added by 1. If we don’t add the number by 1, it just generate a random number
between 0 – 9.
importjava.util.Random;
publicclass Main {
publicstaticvoid main(String[] args) {
Random rand = newRandom();
System.out.println((rand.nextInt(10)+1));
}
}
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Currency Format
In Java, we can get currency format in some country. If we want to get the currency
format in US, we use the class Curency from java.util.Currency. Example:
importjava.util.Currency;
importjava.util.Locale;
publicclass Main {
publicstaticvoid main(String[] args) {
Currency currency = Currency.getInstance(Locale.JAPAN);
System.out.println("Currency.getSymbol() = "
+ currency.getSymbol());
currency = Currency.getInstance(Locale.UK);
System.out.println("Currency.getSymbol() = "
+ currency.getSymbol());
currency = Currency.getInstance(Locale.US);
System.out.println("Currency.getSymbol() = "
+ currency.getSymbol());
currency = Currency.getInstance(new Locale("in", "ID"));
System.out.println("Currency.getSymbol() = "
+ currency.getSymbol());
}
}
Output:
Delay Execution
If we want to make an animation or delay in our program, we can use
delayexecution. There are two kinds of delayexecution: use for(common looping) or
Thread.sleep. Example:
publicclass Main {
publicstaticvoid main(String[] args) {
int loop = 0;
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System.out.print("Loading Menu");
do{
//with the common for
for(inti = 0;i <2000000000;i++);
System.out.print(".");
loop++;
}while(loop < 10);
for(inti = 0;i < 25;i++)
System.out.println();
loop = 0;
System.out.print("Loading Menu");
do{
try {
//with thread.sleep
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.print(".");
loop++;
}while(loop < 10);
}
}
Explanation:
In this code, we use for to delay or execution. If we use i<2000000000 loop statement, it
is too long. If we use Thread.sleep, we just write Thread.sleep(1000) for 1 second. We
must create a try catch to this Thread. The parameter inside Thread.sleep is millisecond.
Calendar Information
In java, there is class Calendar from java.util.Calendar. It is used to get date and time
information. Example:
Import java.util.Calendar;
public class Main {
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public static void main(String[] args) {
do{
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
for(inti = 0;i < 25;i++)
System.out.println();
System.out.println(Calendar.getInstance().getTime());
}while(true);
}
}
Explanation:
In this code, we create the program to get time information. If we run this code, it will
loopinfinitely (that’s not an error) for displayingtime per second.
Reflection Class
In java, Reflection class is used to get information of a class by using
java.util.reflect.*package. There are many classes like Method, Fields and
etc.Reflection is used to get information inside a class.Example:
importjava.lang.reflect.Field;
importjava.lang.reflect.Method;
class People{
private String name;
private int age;
public People(String name,int age){
this.name=name;
this.age=age;
}
Public void setName(String name) {
this.name = name;
}
Public void setAge(int age) {
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this.age = age;
}
public String getName() {
return name;
}
Public int getAge() {
Return age;
}
Public void display(String name, int ages){
System.out.println("I'm "+name+" with age "+ages);
}
}
Public class Main {
Public static void main(String[] args) {
Class <People> obj = People.class;
Field[] attr = obj.getDeclaredFields();
People objPeople = new People("Black", 17);
System.out.print("The Attribut in class People is ");
for(Field val:attr){
System.out.print(val.getName()+", ");
}
try {
Method method = obj.getMethod("getName", null);
System.out.println("\nName: "+method.invoke(objPeople,
null));
Method method2 = obj.getMethod("display", new
Class[]{String.class,int.class});
method2.invoke(objPeople, new Object[]{"White",17});
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
Explanation:
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We create a variable from People.class and we create an array of Field from
java.util.reflect.Field.It’s used to get information of attributes in class People. Then,
if we want to call the method in another class, we must create an object of class
People, and create an object method to store the information of the method.If we
want to call the method, we may use invoke.
Output:
Timer Class
Java has class Timer in java.util.Timer package. It is used to schedule any
acitivites.The class Timer is similary use to Thread.sleep, but class Timer can repeat
an activity. Example:
importjava.util.Date;
importjava.util.Timer;
importjava.util.TimerTask;
/**
* Simple demo that uses java.util.Timer to schedule a task to execute
once 10
* seconds have passed.
*/
publicclass Main {
Timer timer;
public Main(int seconds) {
timer = new Timer();
//new date() to repeat, if we didn't use new date, it just delay
timer.schedule(newRemindTask(),new Date(), seconds * 1000);
}
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classRemindTaskextendsTimerTask {
publicvoid run() {
System.out.println("Time's up!");
//timer.cancel(); //Not necessary because we call System.exit
//System.exit(0); //Stops the AWT thread (and everything else)
}
}
publicstaticvoid main(String args[]) {
System.out.println("About to schedule task.");
new Main(10);
System.out.println("Task scheduled.");
}
}
Explanation:
In this code, if we want to use the class Timer, we create an object of class
Timer.If we want to delay, we must use timer.schedule with parameter the
TimerTask, date(if you want to repeat), and delay.
5. Exercise
For exercise, you make a program that has many functions. First, it can be show
the datetime today, then there is a loading bar to generate random number 3 times
between 5 until 17.Finally,there is a choice to repeat the program or not.If use chooses
not, the program ends, If yes, the program restarts.
a. Task 1: Create Project Java in Eclipse
- Run Eclipse from start Menu
- Open Menu File New Project
- Choose Java Project Fill Project Name example: ―Answer11‖
- Press Finish, and show pop up, choose ―No‖.
b. Task 2: Create the main Class
The Main class is where we write code. We will make the main method where
we will write code in the Main class, and also import java.util.Scanner to use the
Scanner class.
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In this case, we use a global variable to create the scanner object, so it can be
used by every method.
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c. Task 3: Show the time of today
First, we must display the time of today by usingclass Calendar and import
java.util.Calendar.We also create an object of class Random to generate random
numbers.
d. Task 4: create the Random Number with delay
After we display the time, we display delayed random number.
We need variable index to loop 3 times.Variableindexis added by1, and afterthat
starts to loop again.We use delay execution by using Thread.sleepin 20 times looping
to display the dot symbol (―.‖).After loading-process ends, it displays the random
number between 5 until 17.We ask user to get the program repeat or not.
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Code:
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Chapter 12
Introduction to OOP Concept
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Object Oriented Programming (OOP) is a programming paradigm using objects. Some
techniques may include feature such as data abstraction, encapsulation, inheritance, and so on.
Benefits of Object Oriented Programming:
a. The concept of a data class makes it possible to define subclasses of data objects that
share some or all of the main class characteristics. Called inheritance, this property of
OOP forces a more thorough data analysis, reduces development time, and ensures more
accurate coding.
b. Since a class defines only the data it needs to be concerned with, when an instance of that
class (an object) is run, the code will not be able to accidentally access other program
data. This characteristic of data hiding provides greater system security and avoids
unintended data corruption.
c. The definition of a class is reuseable not only by the program for which it is initially
created but also by other object-oriented programs (and, for this reason, can be more
easily distributed for use in networks).
The concept of data classes allows a programmer to create any new data type that is not
already defined in the language itself.
Exercise
Exercise for Object Oriented Programming
a. Blueprint for a software object is called a class
b. An object’s state is stored in fields.
c. An object’s behavior is exposed through methods.
What are the fields and behavior that a human has?
Fields
o Name
o Age
o Gender
o Etc
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Behavior
o Speak
o Walk/Run
o Sleep
o etc
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Chapter 13
Class and Object
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Class Definition
Class is a collection of attribute and method that have similar function or a blueprint from a
object. A class usually represent a noun, such as person, place or thing. For an example, for a
simple program to calculate GPA from student, we will have class called „Student‟ that have
attribute to store data from the student such as NIM, Name, GPA, and Phone number. And
method to calculate GPA like the diagram below:
This diagram, show the structure from class Student
We can transfer that diagram into Java program with this code:
Object Definition
Objects are key to understanding object-oriented technology and a representation from a
class. As we already stated above, there are many examples of class or object, for example: your
bicycle, your computer, your car, your keyboard. Objects share two characteristics: state and
behavior. Bicycles have state (color, pedal, gear) and behavior (changing gear, applying brakes).
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Objects are conceptually similar to real-world object (state and behavior). An object store its
state in fields (variable) and exposes its behavior through methods (function). An object is
defined by using keyword “new”.
This diagram shows the relation between fields (attribute) and methods
In the real world, you’ll find many individual objects all of the same kind. There may be
thousands of car in existence, all of the same make and model. Each car was built from the same
set of blueprints and contains the same components. A class is the blueprint from which
individual objects are created. Look at the example :
As we mentioned above, in the real world, you’ll find many individual objects all of the
same kind. Like an university that have thousand of students, all of their students is have similar
attribute, every student must have a nim, name, gpa, and phone number, the students in the
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university is what we called object from a class, like showed in the picture above, thomas and
claire is a object that represent the class Student.
This following code is a example to make an object from class Student in Java:
Constructor
Each class has its constructor. A constructor is invoked every time an object is created.
Constructor declarations look like method declarations – except that they use the name of the
class and have no return type. Every class may have one or more constructors.
Inner Class
Inner class, or we can say nested class, occurs when you define a class within another class.
Nested classes are divided into two categories: static and non-static. Nested classes that are
declared static are simply called static nested classes. Non-static nested classes are called inner
classes.
Why use nested classes?
It is a way of logically grouping classes that are only used in one place.
It increases encapsulation.
Nested classes can lead to more readable and maintainable code.
Exercise
For exercise, you’ll have to make a program of student. This program has 4 menus (Get info,
Change name, Change GPA, and Exit). Validate each input must between 1 and 4.
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If the user’s input is 1:
If the user’s input is 2:
If the user’s input is 3:
a. Task 1: Defining a class named Student:
First, we will make a class named Student with attribute id, name and gpa, and method to
print the student info. This class is used to store data about Student and accessed in our
Main class.
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b. Task 2: Make the Main Class
The Main class is where we put our code to create the program. We will make the main
method and the constructor where we put our program in the Main class, and also import
java.util.Scanner to use the Scanner class.
c. Task 3: Make a object from Student class and Scanner class.
We will make an object from Student class that we make before, and because we need
user to give input to our program we need the Scanner class in our program.
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d. Task 4: Make viewMenu Method
This method will be used to print the menu from our program
e. Task 5: Make changeName Method
changeName method will ask the user to input a new full name, with input validation the
full name that user inputted must be between 3 and 20 characters long.
f. Task 6: Make changeGPA Method
changeGPA method will ask the user to input a new GPA, with input validation the GAP
that user inputted must be between 0 and 4 in double format.
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g. Task 7: Complete the main method
Here we will complete the main method that we create above with the method we create
like changeName and changeGPA method.
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Chapter 14
Encapsulation
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Encapsulation Concept Definition
Encapsulation is one of the fundamental of OOP concepts. Encapsulation is the technique of
making the fields in a class private and providing access to the fields via public methods. If a
field is declared private, it cannot be accessed by anyone outside the class, thereby hiding the
fields within the class. For this reason, encapsulation is also referred to as data hiding.
Encapsulation can be described as a protective barrier that prevents the code and data being
randomly accessed by other code defined outside the class. Access to the data and code is tightly
controlled by an interface.
The main benefit of encapsulation is the ability to modify our implemented code without
breaking the code of others who use our code. With this feature Encapsulation gives
maintainability, flexibility and extensibility to our code.
Access Modifier
The access to classes, constructors, methods, and fields are regulated using access modifiers.
For example, a class can control what information or data can be accessible by other classes. To
take advantage of encapsulation, you should minimize access whenever possible.
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Java provides a number of access modifiers to help you set the level of access you want for
classes as well as the fields, methods, and constructors in your classes. A member has package or
default accessibility when no accessibility modifier is specified.
Access Modifiers Same Class Same Package Subclass Other
Packages
Public √ √ √ √
Protected √ √ √ ×
No access modifier √ √ × ×
Private √ × × ×
public access modifier
Fields, methods and constructors declared public (least restrictive) within a public class are
visible to any class in the Java program, whether these classes are in the same package or in
another package.
private acess modifier
The private (most restrictive) fields or methods cannot be used for classes and Interfaces. It
also cannot be used for fields and methods within an interface. Fields, methods or constructors
declared private are strictly controlled, which means they cannot be accesses by anywhere
outside the enclosing class. A standard design strategy is to make all fields private and provide
public getter methods for them.
protected access modifier
The protected fields or methods cannot be used for classes and Interfaces. It also cannot be
used for fields and methods within an interface. Fields, methods and constructors declared
protected in a superclass can be accessed only by subclasses in other packages. Classes in the
same package can also access protected fields, methods and constructors as well, even if they are
not a subclass of the protected member’s class.
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no access modifier
Java provides a default specifier which is used when no access modifier is present. Any
class, field, method or constructor that has no declared access modifier is accessible only by
classes in the same package. The default modifier is not used for fields and methods within an
interface.
Let us look at an example code below:
This is how we call its method:
Static Variables
The static keyword is used to create variables that will exist independently of any instances
created for the class. Only one copy of the static variable exists regardless of the number of
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instances of the class. Static variables are also known as class variables. Local variables cannot
be declared static.
Static methods
The static keyword is used to create methods that will exist independently of any instances
created for the class. Static methods do not use any instance variables of any object of the class
they are defined in. Static methods take all the data from parameters and compute something
from those parameters, with no reference to variables.
Class variables and methods can be accessed using the class name followed by a dot and the
name of the variable or method.
Let us look at an example code below:
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Setter Getter
Setter and getter are one of many ways in assigning a value to the fields. Here is the way you
create setter and getter in eclipse IDE:
Right click in the editor, choose Source, and choose Generate Getters and Setters
On the Genereate Getters and Setters Dialog, select the fields you want to generate getters and
setters.
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Click OK when you finished configuring. The result is shown below:
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Exercise
Battle of Padawans - Ep. 1
Blues company is a company enganged in game programming. Once, they want to make a game
named “Battle of Padawans – Ep. 1”. You, as programmer, were asked by the company manager
to make this game using eclipse IDE. Here are the descriptions of the game:
First, program will ask for hero name.
Hero has some status: name, rank, body, mind, and stamina.
The main menu consist of 4 menus:
o Show status
o Train
o Rest
o Quit game
If the user choose “Show status”, then
o Print the name, rank, body, mind, and stamina of the hero.
If the user choose “Train”, then
o Show the “Jedi Training” menus:
Learn lightsaber (body)
Learn force (mind)
Done training
o If the user choose “Learn lightsaber (body)”, then
Lightsaber skill +2
Force power -1
Stamina -1
o If the user choose “Learn force (mind)”, then
Force power +2
Lightsaber skill -1
Stamina -1
o If the user choose “Done training”, then back to main menu
If the user choose “Rest”, then
o The stamina is recovered back to 5.
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If the user choose “Quit game”, then end the program.
How to code:
a. Task 01 – Create Eclipse Java Project
Run Eclipse
Create a java project by selecting menu File -> New -> Project
On the “New Project” dialog, choose “Java Project”
Enter a project name, for example “Exercise 11”
Click Finish
Make a new Class by right clicking on the project folder, choose New -> Class
Enter a class Name, for example “Main”
Finish
b. Task 02 – Initialization
Make a New Class for the hero (Padawan.java)
Field Data Type Modifier Setter/Getter
Name String Private Yes
Rank String Private Yes
Body Integer Private Yes
Mind Integer Private Yes
Stamina Integer Private Yes
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The purpose of using setter getter is you will have to call the set method to assign value
to a field, or call the get method to get the value from a field.
This means of information hiding. We cannot directly assign value into the field, but
calling the set/get method.
For example, getName() is a method to get the name’s value. setName() is a method to
assign value to name.
Make the main class (Main.java)
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Create the clear function
Create the input name statement in the constructor
Create the menu method
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c. Task 03 – Analyze Problems
Create “Show Status” method in Main.java
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Create “Train” method in Main.java
o First, we need to make the menu and its validation
o Second, we create the learn lightsaber method
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o Then we create the learn force method
Last, we create the “Rest” method in Main.java
And the whole code would be like this:
Main.java
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Padawan.java
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Chapter 15
Inheritance
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Inheritance concept definition
Different kinds of objects often have a certain amount in common with each other.
Mountain bikes, road bikes, and tandem bikes, for example, all share the characteristics of
bicycles (current speed, current pedal cadence, and current gear). Yet each also defines
additional features that make them different: tandem bicycles have two seats and two sets of
handlebars; road bikes have drop handlebars; some mountain bikes have an additional chain
ring, giving them a lower gear ratio.
Inheritance is the mechanism through which we can derive classes from other classes. To
derive a class in java the keyword extends is used. Java does not support multiple
inheritances.
Benefits of inheritance is to minimise the amount of duplicate code in an application by
putting common code in a superclass and sharing amongst several subclasses.
Superclass
A java superclass is a class which gives a method or methods to a Java subclass, or we
can say it as parent class. For example, superclass of mountain bike is bike.
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Subclass
A java subclass is a class which inherits a method or methods from a java superclass. For
example, mountain bike is subclass of bike which inherits its superclass method (change
gear, applying brakes, etc).
The result is as shown below:
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As we can see, the first output is “Constructor of Superclass is called”. The Superclass’
constructor must be called first before Subclass’ object can be made. For example, mountain
bike will not exist unless bike is created.
Keyword super
The super keyword is used to access the member (field / method / constructor) of the
super class.
Final class
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A final class cannot be extended. This is done for reasons of security and efficiency.
Many of the java standard library classes are final, for example java.lang.System and
java.lang.String. All methods in a final class are implicitly final.
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Exercise
Battle of Knights – Ep. 2
Blues company is a known company as game producer. This company has been known
because of the first game released “Battle of Padawans – Ep. 1”. The company director has
assigned you, as the programmer, to make the second episode “Battle of Knights – Ep. 2”.
Here are the descriptions of the game:
The game has 2 forces, light and dark force
Hero has 4 attributes: name, saber, evade, and kill.
Each hero has the name, saber, evade, and kill attribute. But light hero has special
ability, is able to use force. And dark hero is able to throw the saber.
For light hero:
o Initial saber = 7, means attack success rate is 70%
o Initial evade = 8, means evade success rate is 80%
o Initial force = 9, means evade success rate is 90%
For dark hero:
o Initial saber = random from 7 – 9, means attack success rate is 70 – 90%
o Initial evade = random from 6 – 8, means evade success rate is 60 – 80%
o Initial throwsaber = 8, menas throw saber success rate is 80%
First, program will ask for hero name
Your hero will automatically join the light force
The game consist of 3 menus:
o Show status
o Battle
o Quit game
If the user choose “Show status”, then:
o Show name and total kills of the hero
If the user choose “Battle”, then:
o Print “An enemy has ambushed you!!”
o The hero has 3 actions: attack, force, and escape
o Your hero strikes first.
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o If the user choose attack:
Attack success is according to the initial saber attack.
If your hero fail to attack, print “Your attack has missed”.
If your hero’s attack success, and enemy evade it, print “Enemy has evaded
your attack”.
If your attack success and enemy fail to evade, print “You have killed the
enemy” and end the battle.
o If the user use force:
Force success is according to the initial force attack.
If your hero fail to force, print “Your force has missed”.
If you’re her’s attack success and the enemy evade it, print “Enemy has
evaded your attack”.
If your attack success and enemy fail to evade, print “You have killed the
enemy” and end the battle.
o If the user use escape, then run from the battle, the hero gains nothing
o At the end of your turn, enemy will do a counter attack. Enemy has a chance 80%
of doing normal attack and 20% of doing saber attack.
If enemy attack fail, print “Enemy attack has missed”.
If enemy attack success and your hero evade it, print “You have evaded
enemy’s attack”
If enemy attack success and your hero fail to evade, print “You have been
killed! Game over”. And the program ends.
If the user choose “Quit game”, then end the program
How to code:
a. Task 01 – Create Eclipse Java Project
Run Elipse
Create a java project by selecting menu File -> New -> Project
On the “New Project” dialog, choose “Java Project”
Enter a project name, for example “Exercise 12”
Click Finish
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Make a new Class by right clicking on the project folder, choose New -> Class
Enter a class name, for example “Main”
Finish
b. Task 02 – Create a superclass
First, we need to create a general hero class, for example Padawan.java
This padawan is the superclass of the Knight Class that we will make later. Every
Light Knight and Dark Knight have name, saber attack, evade rate, and kill ratio.
They can also do attack and get hit. So we need to put these fields and methods in
the Padawan class.
Field Data Type Modifier Setter/Getter
Name String Private Yes
Saber Integer Private Yes
Evade Integer Private Yes
Kill Integer Private Yes
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Next we will fix the attack method, the attack rate is according to saber attack.
For example, if the saber attack is 7, means the attack success rate is 70%. So we
just need to make a random number from 0 to 10.
And so is the hit method:
Okay, the parent class is ready, next we will create the subclass
c. Task 03 – Create a subclass (Part 1)
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There are two hero with different special attack, light hero can do force, on the
other hand, dark hero can throw saber, so we need to make 2 subclasses of
Padawan class.
In this part 1, we will create the Light hero class
Just create a new class, named LightKnight.java
LightKnight have a special attribute, that is force. And special attack, called force.
Force attack is almost the same as normal attack. It has success attack percentage.
d. Task 04 – Create a subclass (Part 2)
Create a new Class named DarkKnight.java
Dark hero can do throw saber attack.
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e. Task 05 – Create the main class
Create the main method
Create the clear screen method
Create the main menu
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Create show status method
Create battle method
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Next, we will code the hero’s move. It starts with user’s input (attack, force, or
escape)
Next step, the hero will attack according to our moves (attack / force / escape)
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Status is just a flag, to indicate whether hero attack success / fail
Last step is attacking to the enemy
Enemy has 80% chance to do normal attack and 20% chance to do special attack.
To make this code, we need to create a new method, for example, enemyAttack()
This is the enemy code:
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f. Here’s the complete code:
Padawan.java
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LightKnight.java
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DarkKnight.java
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Main.java
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Chapter 16
Polymorphism
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Polymorphism Concept Definition
Polymorphism is the ability of an object to take on many forms. The most common use of
polymorphism in OOP occurs when a parent class reference is used to refer to a child class
object.Any java object that can pass more than on IS-A test is considered to be polymorphic.
In java, all java objects are polymorphic since any object will pass the IS-A test for their own
type and for the class Object.
It is important to know that the only possible way to access an object is through a
reference variable. A reference variable can be of only one type.Once declared the type of a
reference variable cannot be changed.The reference variable can be reassigned to other
objects provided that it is not declared final. The type of the reference variable would
determine the methods that it can invoke on the object.
Overloading
Method overloading allows us to have same method name in a class or a subclass,
however, the class / subclass method (overloaded method) should change the argument
compulsarily. This brings us to the conclusion that overloaded methods may all be defined in
the same class, or they may be defined in different classes as long as those different classes
share a superclass.
Overriding
Overriding means creating a new set of method statements for the same method signature
(name, number of parameters and parameter types). The benefit of overriding is: ability to
define a behavior that’s specific to the sub class type. Which means a subclass can implement
a parent class method based on its requirement.
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This would produce the following result:
Casting Object
In casting object, one object reference can be type cast into another object reference. The
cast can be to its own class type or to one of its subclass or superclass types or interfaces. The
casting of object references depends on the relationship of the classes involved in the same
hierarchy. Any object reference can be assigned to a reference.
There are 2 types of casting object: upcasting and downcasting. When we cast a reference
along the class hierarchy in a direction from the root class towards the children or subclasses,
it is a downcast.When we cast a reference along the class hierarchy in a direction from the
sub classes towards the root, it is an upcast.
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Exercise
The Jedi Returns – Ep. 3
Blues company is a known company as a game producer. The company wants to make a
greater game than its anchestor, “Battle of Knights – Ep. 2”. You, as a programmer, is asked
to make this game with title “The Jedi Returns – Ep. 3”. According to the director’s plan, this
game will be the last Starwars game. Here are the descriptions of the game:
Player has 5 lives
Hero can promote himself into higher level, for example, from Knight rank into
Master rank.
Knight rank is only able to attack. Knight initial state is as describe below:
o Initial saber = 7
o Initial evade = 6
o Rank = “knight”
Master rank can either attack or use force. Force attack will not kill the enemy, but
weaken the attack power by 3 for 3 turns. Master is divided into 2 side, the light side
and the dark side.
o For light side:
Rank = “master”
Initial saber = 8
Initial evade = 7
Initial force = 9
o For dark side:
Rank = “master”
Initial saber = 9
Initial evade = 7
Initial force = 8
First, program will asked for hero’s name
The game consist of 4 menus:
o Show status
o Battle
o Choose side (only available for Knight rank and total kills > 5)
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o Quit game
If the user choose “Show status”, then:
o Show the hero’s name, lives, and total kill
If the user choose “Battle”, then:
o If the hero’s rank is Knight, the enemy would be Knight.
o If the hero’s rank is Master, the enemy would be Master also.
o Attack success is according to initial saber attack
If the use choose “Choose side”, then:
o Hero must choose his side, light or dark side.
o If the hero choose light side, promote him into Master (light)
o If the hero choose dark side, promot him into Master (dark)
If the user choose “Quit game”, thenend the program.
How to code:
g. Task 01 – Create Eclipse Java Project
Run Elipse
Create a java project by selecting menu File -> New -> Project
On the “New Project” dialog, choose “Java Project”
Enter a project name, for example “Exercise 13”
Click Finish
Make a new Class by right clicking on the project folder, choose New -> Class
Enter a class name, for example “Main”
Finish
h. Task 02 – Create a superclass
First, we just need to create a general class, for example Knight.java
This “Knight.java” class will be superclass of the Master Class we will create
later. Both Knight and Master have their names, total kills, lives, saber attack,
evade rate, and rank. They can also do attack, get hit, and die.
Field Data Type Modifier Setter / Getter
Name String Private Yes
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Kill Integer Private Yes
Lives Integer Private Yes
Saber Integer Private Yes
iSaber Integer Private Yes
Evade Integer Private Yes
Rank String Private Yes
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Now we will fix the attack method, the attack rate is according to saber attack.
For example, if the saber attack is 7, means the attack success rate is 70%. So we
just need to make a random number from 0 to 10.
And so is the hit method
And the die method
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Okay, the parent class is ready, next we will create the subclass
i. Task 03 – Create a subclass
As we can see, Master is derived from Knight class, so we just need to create
Master Class. Master has some new attributes: side, force, and counter (for force
side effect). Master can do force attack.
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Beside do force attack method, Master can also receive force attack that will
weaken his attack. So we need to create “normalize” method to normalize the
force effect.
j. Task 04 – Create the main class
Create the main method
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Create the clear screen method
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Create the main menu
Create show status method
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Create battle method
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Both Knight and master has different battle option, knight has 2 options, while
master has 3 options. So, we need to check for the hero’s rank first
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Next step, the hero will attack according to our moves (attack / force / escape)
Status is just a flag, to indicate whether hero attack success / fail
Last step is attacking to the enemy
Enemy has 80% chance to do normal attack and 20% chance to do special attack.
To make this code, we need to create a new method, for example, enemyAttack()
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Enemy with knight rank can only do normal attack, but enemy with master rank
can do both normal attack and force attack. So we need to clarify the rank first
This is the enemy attack code
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k. Here’s the complete code:
Knight.java
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Master.java
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Main.java
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Chapter 17
Abstract and Interface
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Abstract Class and Method
An abstract class is a class that is declared abstract – it may or may not include abstract
methods. Abstract classes cannot be instantiated, but they can be subclassed. If a class is
abstract and cannot be instantiated, the class does not have much use unless it is subclassed.
This is typically how abstract classes come about during the design phase. A parent class
contains the common functionality of a collection of child classes, but the parent class itself
is too abstract to be used on its own.
An abstract method is a method that is declared without an implementation (without
braces, and followed by a semicolon). Declaring a method as abstract has two results: first,
the class must also be declared abstract. If a class contains an abstract method, the class must
be abstract as well. Second, any child class (sub class) must either override the abstract
method or declare itself abstract.
An abstract class can contain fields that are not static and final, and they can contain
implemented methods.
Interface
An interface is a collection of abstract methods. A class implements an interface, thereby
inheriting the abstract methods of the interface. An interface is not a class. Writing an
interface is similar to writing a class, but they are two different concepts. A class describes
the attributes and behaviors of an object. An interface contains behaviors that a class
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implements. Unless the class that implements the interface is abstract, all the methods of the
interface need to be defined in the class.
An interface is similar to a class in the followin ways:
An interface can contain any number of methods
An interface is written in a file with a .java extension, with the name of the interface
matching the name of the file
The bytecode of an interface appears in a .class file
Interfaces appear in packages, and their corresponding bytecode file must be in a
directory structure that matches the package name.
However, an interface is different from a class in several ways, including:
An interface cannot be instantiated
An interface does not contain any constructors
All of the methods in an interface are abstract
An interface cannot contain instance fields. The only fields that can appear in an
interface must be declared both static and final.
An interface is not extended by a class, it is implemented by a class
An interface can extend multiple interfaces
A class can implement multiple interfaces
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Exercise
Geome-Try
Math Corp is a corporation engaged in education. This corporation want to make a
simulation about geometry such as Rectangle, Square, and Triangle to elementary students all
over the world. You, as the programmer, is asked to make this program using eclipse IDE.
Here are the descriptions of the program.
Program has 4 menus:
o Rectangle
o Square
o Triangle
o Exit
If the user choose “Rectangle”, then
o Ask user’s input for width and height of the rectangle.
o Vaildate that the input is number and between 1 and 10
o Draw the rectangle
o Get the description of the rectangle (width, height)
o Calculate the area
If the user choose “Square”, then
o Ask user’s input for side of the square.
o Vaildate that the input is number and between 1 and 10
o Draw the square
o Get the description of the square (side)
o Calculate the area
If the user choose “Triangle”, then
o Ask user’s input for height and base of the square.
o Vaildate that the input is number and between 1 and 10
o Draw the triangle
o Get the description of the square (height, base)
o Calculate the area
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Draw the rectangle and get the description above the main menu after the user has chosen
a menu.
How to code:
a. Task 01 – Create Eclispe Java Project
Run Elipse
Create a java project by selecting menu File -> New -> Project
On the “New Project” dialog, choose “Java Project”
Enter a project name, for example “Exercise 14”
Click Finish
Make a new Class by right clicking on the project folder, choose New -> Class
Enter a class name, for example “Main”
Finish
b. Task 02 – Create an abstract class
As we can see, rectangle, square, and triangle is a shape. A shape has its area and it
has a shape to draw.
Create an abstract class, for example, “Shape.java” which has 2 abstract methods:
getArea() and draw()
getArea() and draw() are an abstract method that must be overridden in Shape class’
subclasses.
c. Task 03 – Create Rectangle class
A rectangle has both width and height. Once a rectangle is made, it has its width and
height.
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The image above is the illustration of coding the rectangle
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The getArea() method is a method that will return the result of width multiplied by
height.
d. Task 04 – Create Square class
Square is almost the same as rectangle, but has the same width and height. So, we just
assume it has side.
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The getArea() method is a method that will return the result of side quadrate.
e. Task 05 – Create Triangle class
Triangle only has its height and base.
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The getArea() method is a method that will return the result of half the base time the
height.
f. Task 06 – Create the main class
Create the main method
Create the clear screen method
Create the main menu
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Create the rect() method
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Create the square() method
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Create the triangle() method
g. Here is the complete code:
Shape.java
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Rectangle.java
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Square.java
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Triangle.java
Main.java
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Chapter 18
Package
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A java package is a set of classes which are grouped together. This grouping helps to
organize Java classes and codevent multiple Java classes with the same name.
Creating and Naming Package
This is how to make and name a package:
right click on the src folder, then choose new -> package
On the “new Java Package” dialog, type the package name:
Press Finish.
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After pressing finish, you will see in the project explorer the new package you have just
made.
Next, you can create/import existing class into this package.
Using Package
To use a package in your Java source code, you must either import the package or use the
fully qualified class name each time you use a class. In this example,there are 2 packages, each
package contains 1 class:
From Main.java, we want to create an instance of DemoClass. This shows you how to do it:
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Let’s take a look at the code above. The first line is “package mainProgram;”, this means the
Main class is inside the mainProgram package. The next statement is “import
myClass.DemoClass;”, this means we want to import DemoClass class from myClass package.
Beside this way, you can use “import myClass.*;”, where * means import all public classes from
myClass package.
There are 2 ways in using packages:
The first way, you have to import the class’ package, so that you can use that class to
create instances.
The second way, you have to use the [package name].[class name] to create instances.
For example: “myClass.DemoClass demo2 = new myClass.DemoClass(“Demo 2”);”
Exercise
Zooooo
Zooooo kindergarden is planning on making a program about animal. They want to brief
to the children about animals. The program is to give some descriptions about the animal
they choose. You, as the programmer, is asked to make this program using eclipse IDE. Here
are the descriptions of the program:
Program consists of 3 menus:
o Visit aves family
o Visit reptile family
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o Go home
If the user choose “Visit aves family”, then:
o Show another 3 menus:
Eagle
Owl
Exit
o If the user choose “Eagle”, then
Show the descriptions of Eagle
“Eagles are members of the bird family Accipitridae, and belong to several genera
which are not necessarily closely related to each other. Most of the more than 60
species occur in Eurasia and Africa.”
Print the sound of eagle
Eagle is chirping
Twit.. twit.. twit..
o If the user choose “Owl”, then
Show the descriptions of Owl
Owls belong to the order Strigiformes, constituting 200 extant bird of prey
species.
Most are solitary and nocturnal, with some exceptions (e.g. the Northern Hawk
Owl).
Owls hunt mostly small mammals, insects, and other birds, although a few species
specialize in hunting fish.
Print the sound of owl
Owl is hooting
Whoo... whoo... whoo...
o If the user choose “Exit”, then back to main menu
If the user choose “Visit reptile family”, then:
o Show another 3 menus:
Snake
Crocodile
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Exit
o If the user choose “Snake”, then
Show the descriptions of Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that
can be distinguished from legless lizards by their lack of eyelids and external ears.
Many species of snakes have skulls with many more joints than their lizard
ancestors, enabling them to swallow prey much larger than their heads with their
highly mobile jaws.
Print the sound of Snake
Snake is hissing
hisss........
o If the user choose “Crocodile”, then
Show the descriptions of Crocodile
A crocodile is any species belonging to the family Crocodylidae (sometimes
classified instead as the subfamily Crocodylinae).
The term can also be used more loosely to include all extant members of the order
Crocodilia
Print the sound of eagle
Crocodile is silent
...........
If the user choose “Go home”, then end the program.
How to code:
a. Task 01 – Create Eclipse Java Project
Run Elipse
Create a java project by selecting menu File -> New -> Project
On the “New Project” dialog, choose “Java Project”
Enter a project name, for example “Exercise 15”
Click Finish
Make a new Class by right clicking on the project folder, choose New -> Class
Enter a class name, for example “Main”
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Finish
b. Task 02 – Create aves and reptile package
Eagle and Owl is 1 type, so we just need to make a package of it, for example, “aves”
package.
Right click on the project, choose New -> Package, give package name: aves
Finish
Next, we will create the reptile package
So, the result would be like this:
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c. Task 03 – Create Eagle and Owl class
We will create 2 classes in the aves package
First, create a new Class, named Eagle
You will nothice that additional “package aves” is added in top of your code. This
means Eagle class is inside the aves package.
Next, we will code its behavior, such as speak and description.
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And so is the Owl class
d. Task 04 – Create Snake and Crocodile class
We will create 2 classes in the reptile package, the Snake and Crocodile class
Snake class
Crocodile class
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e. Task 05 – Create the main class
Create the main method
Create the clear screen method
Create the main menu
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Create the aves method
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Create the reptile method
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f. Here is the complete code:
aves
Eagle.java
Owl.java
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reptile
Snake.java
Crocodile.java
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Main.java
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Chapter 19
Basic Class in Java
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1. Wrapper Class
Each of Java's eight primitive data types has a class dedicated to it. These are known as
Wrapper Class, because they "wrap" the primitive data type into an object of that class. So,
there is an Integer class that holds an int variable, there is a Double class that holds a double
variable, and so on. The wrapper classes are part of the java.lang package, which is imported
by default into all Java programs.
The following two statements illustrate the difference between a primitive data type
and an object of a wrapper class:
We usually use wrapper class for convert string to number. If we have string “12”, we
can’t use mathematical operation for that string. If you want to do that we must convert that
string to a number first. For example we will convert that string to Integer.
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After we convert the string “12” to Integer, we can use mathematical operation.
2. String Class
The String Class represents character strings. String is a collection of some characters
into an array (Array of Character). There are several ways that can be used to make a string.
For example, if we want to create “Hello World” string, we can use this code:
String also could be create from a collection of characters like this code:
The class String includes methods for examining individual characters of the sequence,
for comparing strings, for searching strings, for extracting substrings, and for creating a copy
of a string with all characters translated to uppercase or to lowercase. For example if we
want to know length of string “Hello World”, we can use this code:
The result from code above is 11, which means that the number of characters that exist
on the object “msg1” is 11.
There are many other methods that can be use for String Class. Below we can see some
methods that are often used:
Return
Type
Method Explanation
char charAt(int index) Returns the character at the specified
index.
int compareTo(String another
String)
Compares two strings lexicographically.
int compareToIgnoreCase(S Compares two strings lexicographically,
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tring str) ignoring case differences.
String concat(String str) Concatenates the specified string to the
end of this string.
boolean equals(Object anObject) Tests if this string ends with the specified
suffix.
boolean equalsIgnoreCase(String
anotherString)
Compares this String to another String,
ignoring case considerations.
int length() Returns the length of this string.
String[] split(String regex) Splits this string around matches of the
given regular expression.
String substring(int beginIndex,
int endIndex)
Returns a new string that is a substring of
this string.
String toLowerCase() Converts all of the characters in this
String to lower case using the rules of the
default locale.
String toUpperCase() Converts all of the characters in this
String to upper case using the rules of the
default locale.
String trim() Returns a copy of the string, with leading
and trailing whitespace omitted.
3. Math Class
The Math Class contains methods for performing basic numeric operations such as the
elementary exponential, logarithm, square root, and trigonometric functions.
There are 2 constant number in Math Class, there are phi and E.
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Here is the example of Math Method:
Trigonometric Method
Exponent Method
If we want to make 23 we can use this code:
If we want to make 25 we can use this code:
Rounding Method
Random Method
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4. Exercise
For excercise we will make a simple program.
Program consists of 4 menus:
1. Input String
2. See String
3. Rounding Number
4. Exit
If user chooses Input String, then:
- Ask user to input a string. Validate that the length of the string must be between 5
and 20.
If user chooses See String, then:
- Validate if user never Input String (Menu 1), then show message “You must input a
string first”.
- If user already input the string then show:
String that user inputed.
Length of the string.
The string in Upper Case.
The string in Lowwer Case.
If user chooses Rounding Number, then:
- Ask user to input a number. Validate that the number must between 1.0 and 5.0 and
must be a number.
- Show:
Number that user Inputed.
Numer after ceil.
Numer after floor.
Numer after rint.
Numer after round.
If user chooses Exit, then:
- Program ends.
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a. Task 01 - Create Project
1. Run Eclipse from Start Menu
2. Open Menu File -> New -> Java Project
3. Enter Project Name “Chap16”
4. Then Press Finish
5. Expand Project folder
6. Right click on src -> new -> class
7. Enter Class Name “Main”
8. Then Press Finish
b. Task 02 – Make a class named StringEdit
1. Right click on src -> new -> class
2. Enter Class Name “StringEdit”
3. Then Press Finish
4. Double Click at StringEdit.java
5. We will make a class named StringEdit for store string data with attribute str, a
constructor, setter and getter for str, and 3 method (strLength, strUP, strLOW). We
will use method strLength() for get the length of the str, strUP to make Upper Case str
and strLOW to make Lower Case str.
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c. Task 03 – Make the Main class
1. Double Click at Main.java
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2. Add a global Scanner for input and an global object from class String Edit
d. Task 04 – Make clear method in main class
We will make a method named “clear” for clear our screan.
e. Task 05 – Make menu1 method in main class
We will make a method named “menu1”. We will call it if user choose menu 1 (Input
String). We must validate the length of the string must be between 5 and 20.
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f. Task 06 – Make menu2 method in main class
We will make a method named “menu2”. We will call it if user choose menu 2 (See
String).
1. First we will validate if user never input the string
sEdit.getStr() -> get the value of String
equals(“”) -> compare string that we get with string ””(empty).
2. Show the result
g. Task 07 – Make menu3 method in main class
We will make a method named “menu3”. We will call it if user choose menu 3
(Rounding Number).
1. First we will validate input must be number and between 1.0 – 5.0
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2. Show the result
h. Task 08 – Make Menu validation in void main
In void main we will make menu validation and call the method that we have made.
1. Print menu option and looping menu
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2. Input menu
3. Selection menu
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Chapter 20
Data Structure in Java
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Data structure is a collection of data that has been developed in a certain mode. Structure not
only store data, but also supports operations to access and manipulate data. In OOP, Data
Structure = Collection. Where an object that stores other objects, referred to as data or elements.
1. ArrayList
ArrayList are implemented with an underlying array, and when that array is full and an
additional element is added, a new, larger, array is allocated and the elements are copied
from the old to the new. Because it takes time to create a bigger array and copy the elements
from the old array to the new array, it is a slightly faster to create an ArrayList with a size
that it will commonly be when full. Of course, if you knew the final size, you could simply
use an array. However, for non-critical sections of code programmers typically don't specify
an initial size.
ArrayList has these characteristics:
An ArrayList automatically expands as data is added.
Access to any element of an ArrayList is O(1). Insertions and deletions are O(N).
An ArrayList has methods for inserting, deleting, and searching.
An ArrayList can be traversed using a foreach loop, iterators, or indexes.
The following functions are frequently used in the ArrayList class
add(element) adding element to the list
clear() delete all element in the list
clone() returns the copied object in the list
containts(element) searching element contains in the list
get(index) take a certain element at index in list
isEmpty() to check whether the list is empty or no
remove(index) to remove the designated element in the list
size() number of element in the list
set(index, element) fill an element in the list in accordance with the
designated position
Example of ArrayList:
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2. Vector
Vectors are commonly used instead of arrays, because they expand automatically when
new data is added to them. The Java 2 Collections API introduced the similar ArrayList data
structure. ArrayLists are unsynchronized and therefore faster than Vectors, but less secure in
a multithreaded environment. The Vector class was changed in Java 2 to add the additional
methods supported by ArrayList.
The following functions are frequently used in the ArrayList class
addElement(element) adding element to the final sequence of
the vector
capacity() restore the capacity vector
clone() restore object coppied in that vector
containts(element) searching element in the vector
copyInto(element[]) copy element ke specific array
elementAt(index) take the element of the designated
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index
insertElementAt(element , index) add an element to the designated index
isEmpty() check whether the vector is empty or
not
remove(index) remove the designated element in the
vector
size() number of elements in vector
set(index, element) fills a vector element in accordance
with the designated position
Example of Vector:
3. ArrayList VS Vector
Each method Vector given keyword “synchronized”, so that when executed in the
Thread, it will not happen Thread congestion.
In ArrayList every method not given keyword “synchronized”, so when executed in
Thread, this can resulted unsafe Thread, in other words collision of Thread can occur,
when Thread try to call ArrayList Method.
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Time used by ArrayList is shorter as compared to Vector.
If we want to create dynamic array run using a Thread, use Vector. Whereas if
indeed the process that we do not need to use threads, then use the ArrayList to faster
processing of dynamic arrays.
4. Exercise
For excercise we will make a simple program.
First the program will show index of vector, name and age.
Program consists of 3 menus:
1. Add
2. Delete
3. Exit
If user chooses Add, then:
- Ask user to input name. Validate that the length of the name must be between 2 and
5 characters.
- Ask user to input age. Validate that the age must be between 10 and 100.
- Add name and age to vector.
If user chooses Delete, then:
- Validate if vector is empty, then show message “Vector empty!!!”.
- Else Ask user to input index of vector. Validate that the index must be between 0 and
maximum index of vector.
- Remove data from vector base on inputed index.
If user chooses Exit, then:
- Program ends.
i. Task 01 - Create Project
1. Run Eclipse from Start Menu
2. Open Menu File -> New -> Java Project
3. Enter Project Name “Chap17”
4. Then Press Finish
5. Expand Project folder
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6. Right click on src -> new -> class
7. Enter Class Name “Main”
8. Then Press Finish
j. Task 02 – Make a class named Data
1. Right click on src -> new -> class
2. Enter Class Name “Data”
3. Then Press Finish
4. Double Click at Data.java
5. We will make a class named Data for store data with attribute name and age, a
constructor, setter and getter for both name and age.
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k. Task 03 – Make the Main class
1. Double Click at Main.java
2. Add a global Scanner for input and an global vector that have Class Data as generic
type.
l. Task 04 – Make clear method in main class
We will make a method named “clear” for clear our screan.
m. Task 05 – Make view method in main class
We will make a method named “view”. We will use it for show index of vector, name
and age that obtained from vector we made.
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1. Create view method
2. View index
This looping will increase the value of variable “i” start from 0 until the total data in
vector(size of vector) and it will print the value of “i”.
3. View name
This looping will increase the value of variable “i” start from 0 until the total data in
vector(size of vector) and it will print name base on index of vector. vec.get(i) -> get
data (Class Data) from Vector “vec” base on index “i”.
getName() -> method from Class data that return the value of attribute “name”.
4. View age
This looping will increase the value of variable “i” start from 0 until the total data in
vector(size of vector) and it will print age base on index of vector. vec.get(i) -> get
data (Class Data) from Vector “vec” base on index “i”.
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getAge() -> method from Class Data that return the value of attribute “age”.
n. Task 06 – Make menu1 method in main class
We will make a method named “menu1”. We will call it if user choose menu 1 (Add).
1. Make menu1 method and make 2 temporary variable 1 String for name and 1 int for
age
2. Input name, validate legth of the name must between 2-5 characters
3. Input age, validate age must between 10-100
4. Add to vector
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Add data to vector. Because the type of vector that we made is Class Data, then we
add new object to the Vector.
o. Task 07 – Make menu2 method in main class
We will make a method named “menu2”. We will call it if user choose menu 2 (Delete).
1. First validate if vector is empty
2. Input index, Validate that the index must be between 0 and maximum index of vector.
3. Remove, remove data from vector base on inputed index
Remove data from Vector base on index that user inputed.
p. Task 08 – Make Menu validation in void main
In void main we will make menu validation and call the method that we have made.
1. Print menu option and looping menu
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2. Input menu
3. Selection menu
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Chapter 21
File
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1. File
In Java we can make a file to stored all data of programs that we make. Before we study
that data stored in variables, arrays and objects are temporary, when the program ends then it
will lose all that has been stored. If we make a file, we can save the data. Each file is placed
in a directory in the file system.
Example : c:\library\bookA.txt
File name : bookA.txt
Directory path : c:\library\
The files and directories are accessed and manipulated by the class java.io.File
Declaration:
If you want to make a file use method createNewFile();
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If you want to make a directory use method mkdir();
The file will be made inside project directory.
The following functions in the class file
canRead() check whether the file can be read
canWrite() check whether the file can be written
exists() check if file exists
getName() restore a file name srting
getPath() return the form srting path of the file
getParent() return the parent directory of the current directory or
the files are placed
isFile() check whether the object is a file or not
isHidden() check whether the type is hidden or not
lastModified() display the last time of modification
length() displays the file size
renameTo(File dest) change the file name to the abstract path name, etc.,
can be seen again in Java help
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Static variable
File.separator string with file separator
File.separatorCha char with file separator
File.pathSeparator string with file separator
File.pathSeparatorChar char with file separator
2. Write File
We will use class PrintWriter for write data in files of type text.
Declaration:
When constructor called it will create a file, if it is missing then the file will be created or
if the file exists then its contents will be discarded. Don’t forget to close the PrintWriter after
finish writing.
Boolean “true” in FileWriter means that you will add the text in the end of file, if you
change it to “false” it will overwrite the old text with the new one.
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Handling used I/O exception.
Result:
The following functions are used
print(value) Write the value in the file can be a string, char, int, double.
long, float, boolean or array of characters.
println(value) Same as the print value by adding a new line int the end.
close() Close connection to the file stream
flush() Clear connection to the file stream
3. Read File
Scanner Class can also be used to read data from a file.
Declaration:
First you must make a file named “data.txt” in project folder. Fill the file with text. In this
example I will add text “The quick brown fox jump over the lazy dog”.
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Result:
Handling used I/O exception.
Function in the Scanner
close() Closes this scanner.
hasNext() Returns true if this scanner has another token in its input.
next() Finds and returns the next complete token from this scanner.
nextLine() Advances this scanner past the current line and returns the input
that was skipped.
nextInt() Scans the next token of the input as an int.
nextFloat() Scans the next token of the input as a float.
nextLong() Scans the next token of the input as a long.
nextDouble() Scans the next token of the input as a double.
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6. Exercise
For excercise we will make a simple program.
Program has 1 file named “data.txt” witch contains data”
“Browniz#dog”
“Lucy#cat”
“Prikitiw#bird”
First program will read data from file “data.txt” and store it to a vector;
Program consists of 2 menus:
1. Add new data
2. Exit and Save
If user chooses Add new data, then:
- Ask user to input name of pet. Validate that the length of the name must be
between 1 and 15.
- Ask user to input type of pet. Validate that the length of the type must be between
1 and 15.
- Add data to vector
If user chooses Exit and Save, then:
- Write data from vector to file “data.txt”.
- Program ends.
a. Task 01 - Create Project
1. Run Eclipse from Start Menu
2. Open Menu File -> New -> Java Project
3. Enter Project Name “Chap16”
4. Then Press Finish
5. Expand Project folder
6. Right click on src -> new -> class
7. Enter Class Name “Main”
8. Then Press Finish
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b. Task 02 - Create File “data.txt”
1. Open Project folder
2. Add new txt file in the folder
3. Named it “data.txt”
4. Add the data.
c. Task 03 – Make a class named Pet
1. Right click on src -> new -> class
2. Enter Class Name “Pet”
3. Then Press Finish
4. Double Click at Pet.java
5. We will make a class named Pet for store pet data with attribute name and type,
getter for both name and type, and a Constructor.
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d. Task 04 – Make the Main class
1. Double Click at Main.java
2. Add a global Scanner for input and an global vector that have Class Pet as generic
type.
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e. Task 05 – Make clear method in main class
We will make a method named “clear” for clear our screan.
f. Task 06 – Make readFile method in main class
We will make a method named “readFile”. We will use it for read data from file
“data.txt” then stored it to vector.
1. First we will validate if “data.txt” never created.
Make a temporary array of string variable
First we define a file name “data.txt” with class File
We validate it with method exists().
If the return is false then “data.txt” is missing
If the return is true then “data.tst” exists
2. Read File
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sn.hasNextLine() -> looping until there are no data that can be read.
sn.nextLine().split(“#”) -> split the string that read from file base on String “#” and
store it to array temp.
Example:
If the program read String “abc#def” then it will be split into String “abc” and
“def”. After that, the string will be stored to array temp.
temp[0] = “abc”
temp[1] = “def”
vec.add() -> Add data to vector. Because the type of vector that we made is Class
Pet, then we add new object to the Vector.
g. Task 07 – Make writeFile method in main class
We will make a method named “writeFile”. We will use it for write data from file
vector stored it to file “data.txt”.
This looping will increase the value of variable “i” start from 0 until the total data in
vector(size of vector) and it will print to file “data.txt” name and type base on index of
vector.
vec.get(i) -> get data (Class Pet) from Vector “vec” base on index “i”.
getName() -> method from Class Pet that return the value of attribute “name”.
getType() -> method from Class Pet that return the value of attribute “type”.
h. Task 08 – Make view method in main class
We will make a method named “view”. We will use it for show all data in vector.
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This looping will increase the value of variable “i” start from 0 until the total data in
vector(size of vector) and it will print name and type base on index of vector.
vec.get(i) -> get data (Class Pet) from Vector “vec” base on index “i”.
getName() -> method from Class Pet that return the value of attribute “name”.
getType() -> method from Class Pet that return the value of attribute “type”.
i. Task 09 – Make menu1 method in main class
We will make a method named “menu1”. We will call it if user choose menu 1 (Add
new data). Make 2 temporary String variable.
1. Input name, Validate that the name must be between 1 and 15
2. Input type, Validate that the type must be between 1 and 15
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3. Add to Vector
Add data to vector. Because the type of vector that we made is Class Pet, then we
add new object to the Vector.
j. Task 10 – Make Menu validation in main class
1. Read File
2. Menu Validation
3. Write File
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Chapter 22
Thread
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1. Theory
Thread: sequence of execution from beginning to end in a program, actually similar to the
process, but how to share resources among processes with threads that are very different. A
thread provides the mechanization of the executed command. A set of instructions executed
in parallel with the time-scale method (when one processor make the shift from one thread
to another thread).
Task: program units that execute independently from one part of the program.
Multiprocessing: the use of two or more CPU in a computer system.
Multitasking: a method to run more than one process where there is sharing of resources
such as CPU.
Multithreading: a way that allows execution of multiple threads going on in a process,
sharing of resources but can be run independently. Multiple thread can be executed in
parallel on a computer system. Multiple thread can make the program more responsive and
interactive and to improve program performance.
There are three models multithreading:
1. Many to One (Solaris Green Thread and GNU Portable Thread)
2. One to One (Windows NT/XP/2000 , Linux, Solaris 9 and above)
3. Many to Many (Windows NT/2000, Solaris prior versions of nine )
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Advantage of multithreading is categorized into four sections:
Responsive
Sharing resources
Economical
Utilization of multiprocessor architectures
The following methods are methods in class Thread
start() Start a thread with the function running in the class. implementing
the Runnable interface and is run by the JVM.
isAlive() find out whether the thread running or not.
setPriority(p : int) thread priority set from 1 to 10.
join() wait for some thread to finish.
sleep(t : long) create a thread to sleep in the size of millisecond.
yeild() stop the thread while and allow another thread to the road.
interrupt() interrupts thread.
2. Exercise
For excercise we will make a simple thread.
We will make 2 process:
- Process 1 will show number from 1 to 10.
- Process 2 will show number from 1 to 10.
Give 1 second delay for each process
a. Task 01 - Create Project
1. Run Eclipse from Start Menu
2. Open Menu File -> New -> Java Project
3. Enter Project Name “Chap21”
4. Then Press Finish
5. Expand Project folder
6. Right click on src -> new -> class
7. Enter Class Name “Main”
8. Then Press Finish
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b. Task 02 – Make a class named Tasks
1. Right click on src -> new -> class
2. Enter Class Name “Tasks”
3. Then Press Finish
4. Double Click at Tasks.java
5. We will use this class for 2nd
process. We will make a class Tasks that have Class
Runnable as interface. Don’t forget to add unimplemented methods.
Click on a the error mark and choose “add unimplemented methods”.
6. Print message for 2nd
process
This looping will increase the value of “i” from 1 to 10.
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Thread.sleep(1000); -> use for make a delay, 1000 means 1000 milliseconds. It
must surond with try-catch.
c. Task 03 – Make the Main class
1. Double Click at Main.java
2. Make object from Class Tasks
3. Make object from Class Thread
Add object from Class Tasks (ts) in Thread Constructor. This means that the thread
will runs Method run in Tasks Class
4. Start the thread
5. Print message for 1st process
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This looping will increase the value of “i” from 1 to 10.
Thread.sleep(1000); -> use for make a delay, 1000 means 1000 milliseconds. It must surond
with try-catch.
Result:
Process 1 will run together with Process 2.
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Chapter 23
Generic
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1. Generic
Generic Programming Facility was added to the Java programming language in 2004 as
part of J2SE 5.0. Generic allows types or functions to be operated in different types of data
objects at compile time. Defining a class or function with a generic type that can be replaced
with concrete data types by the compiler. Strings and Numbers is the kind of concrete data
to overwrite the generic data type.
Advantage of Generic Class
Allows compile time error detection when (compile) compared to the time of the
program (runtime).
A generic class or function allows us as programmers to create certain types of objects
or functions that will be created.
Example interface with generic type
Where <T> considered as formal generic type, which can in substitutes with type specific
later. Substitution of a generic type called a generic instantiation. Generic type must be a
reference for other types. It can not be replaced with primitive data types such as int, double
or char. Capital like the letter T and E is always used to refer to generic types. ArrayList,
iterator, LinkedList and Vector are examples of generic classes.
2. Wildcard
Type parameter with the form“?”.Providing the right kind of element of an object with an
unknown wildcard, placed restrictions on the type of function called in an object. List<?>
indicates that a list has an unknown object type.
Type of Wildcard:
Unbounded wildcard to form ? extends Object example:
<? Extends Number> is a wildcard type is a reference to the number.
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Bounded wildcard to form ? extends T where the wildcard reference to the type T.
Lower bound wildcard to form ? super T where the reference to the type of super T.
Example:
<? extends Number> is a kind of wildcard that refers Number class or subtype Number
class. So we can call with:
max(new TesGenerik<Integer>());
max(new TesGenerik<Double>());
3. Exercise
For excercise we will make a simple Generic and Wildcard.
a. Task 01 - Create Project
1. Run Eclipse from Start Menu
2. Open Menu File -> New -> Java Project
3. Enter Project Name “Chap21”
4. Then Press Finish
5. Expand Project folder
6. Right click on src -> new -> class
7. Enter Class Name “Main”
8. Then Press Finish
b. Task 02 – Make a class named Tasks
1. Right click on src -> new -> class
2. Enter Class Name “Num”
3. Then Press Finish
4. Double Click at Tasks.java
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5. In this class we will make Generic Class with a setter and a getter as Methods.
setNum() -> method for add value to obj
getNum() -> method for get value from obj
c. Task 03 – Make the Main class
1. Double Click at Main.java
2. Make object wildcard
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Make a wildcard that extends Class Number, this object can only be replace with
Byte, Double, Float, Integer, Long, Short
3. Make object generic
Make object from class Num that have generic Integer and Double
4. Set Number
Add Number to object intNum = 100 and douNum = 10.7
5. Print Number
Inserted intNum value to num then print the value of num (result 100)
Inserted douNum value to num then print the value of num (result 10,7)