Java 101: Intro to Java Programming

Introduction

• Your Name : Kanke Ishaku (KayKay)• Your day job: Software Engineer• Your last holiday destination?– UK: Dover– Outside UK: Mallorca, Spain

Java 101

• Java Fundamentals– Setting up your development environment– Language Overview– How Java Works– Writing your first program– Built-in Data Types– Conditionals and Loops

Java 102

• Object-oriented Programming– Classes and Objects– Polymorphism, Inheritance and Encapsulation– Functions and Libraries

Java 103

• Data Structures– Arrays– Collections– Algorithms

Java 101: Introduction to Java

Setting up your Development Environment

Installing Java Development Kit• Download latest Java SE 8 JDK (not JRE) from

http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html

• For Windows, – download the X86 version, double click the .exe file and follow the instructions,

accepting all default• For MACs,

– check if java already installed (javac –version) and if not, download the JDK dmg file, run it and follow the instructions.

• After installation is complete, type javac –version in the Command window (Terminal window on MAC OS)- – The reported version should be 1.8.... – If not, you may need to modify the system variable PATH to include the bin

directory of JDK

What is an IDE?

• IDE = Integrated Development Environment • Makes you more productive • Includes text editor, compiler, debugger, context-

sensitive help, works with different Java SDKs • Eclipse is the most widely used IDE • Alternatives:– IntelliJ IDEA (JetBrains) – NetBeans (Oracle)

Installing Eclipse

• Download and install the latest Eclipse for Java EE (32 Bit version) from http://www.eclipse.org/downloads

• Unzip the content of the archive file you downloaded

• To start Eclipse– On PC, double-click on Eclipse.exe – On Mac, double click Eclipse.app in Application

folder

Hands-on Exercise

Intelli j Setup & Demohttps://www.jetbrains.com/idea/download/

Java 101: Introduction to Java

Language Overview

Java Language Overview

Java Editions

• Java SE: Java Standard Edition • Java EE: Java Enterprise Edition (a.k.a. J2EE)– includes a set of technologies built on top of Java

SE: Servlets, JSP, JSF, EJB, JMS, et al. • Java ME: Java Micro Edition• Java Card for Smart Cards• All Java programs run inside the Java Virtual

Machine (JVM)

JDK vs. JRE

• Java Development Kit (JDK) is required to develop and compile programs

• Java Runtime Environment (JRE) is required to run programs.

• Users must have JRE installed, • Developers must have the JDK installed• JDK includes the JRE

Java 101: Introduction to Java

How Java Works

How Java Works

Java File Structure

Java 101: Introduction to Java

Writing Your First Program

Writing Your First Java Program• Create a new project in your IDE named Java101• Create a HelloWorld class in the src folder inside the Java101

project as illustrated below.

Compiling Your First Java Program• Save the HelloWorld class in the IDE• Run your program: right-clicking and selecting Run

As>Java Application• This automatically compiles the HelloWorld.java file into

into a HelloWorld.class file• Go to the folder you created the Java101 project on your

hard disk and open the src(eclipse) or out (Intelli j)folder.• What do you see?

Anatomy of a Java ApplicationComments Class Name

Access modifier

Function/static method

Arguments

Built-in classes

Introduction to Java

Built-in Data Types

Built-in Data Types• Data type are sets of values and operations

defined on those values.

Basic Definitions

• Variable - a name that refers to a value.• Assignment statement - associates a value with a

variable.

String Data Type

Data Type Attributes

Values sequence of characters

Typical literals “Hello”, “1 “, “*”

Operation Concatenate

Operator +

• Useful for program input and output.

String Data Type

String Data Type• Meaning of characters depends on context.

String Data Type

Expression Value

“Hi, “ + “Bob” “Hi, Bob”

“1” + “ 2 “ + “ 1” “ 1 2 1”

“1234” + “ + “ + “99” “1234 + 99”

“1234” + “99” “123499”

Hands-on Exercise

Command Line Arguments

Exercise: Command Line Arguments

• Create the Java program below that takes a name as command-line argument and prints “Hi <name>, How are you?”

Integer Data Type

Data Type Attributes

Values Integers between -2E31 to +2E31-1

Typical literals 1234, -99 , 99, 0, 1000000

Operation Add subtract multiply divide remainder

Operator + - * / %

• Useful for expressing algorithms.

Integer Data TypeExpression Value Comment

5 + 3 8

5 – 3 2

5 * 3 15

5 / 3 1 no fractional part

5 % 3 2 remainder

1 / 0 run-time error

3 * 5 - 2 13 * has precedence

3 + 5 / 2 5 / has precedence

3 – 5 - 2 -4 left associative

(3-5) - 2 -4 better style

3 – (5-2) 0 unambiguous

Double Data Type

• Useful in scientific applications and floating-point arithmetic

Data Type Attributes

Values Real numbers specified by the IEEE 754 standard

Typical literals 3.14159 6.022e23 -3.0 2.0 1.41421356237209

Operation Add subtract multiply divide

Operator + - * /

Double Data TypeExpression Value

3.141 + 0.03 3.171

3.141 – 0.03 3.111

6.02e23 / 2 3.01e23

5.0 / 2.0 1.6666666666667

10.0 % 3.141 0.577

1.0 / 0.0 Infinity

Math.sqrt(2.0) 1.4142135623730951

Java Math Library

Methods

Math.sin() Math.cos()

Math.log() Math.exp()

Math.sqrt() Math.pow()

Math.min() Math.max()

Math.abs() Math.PI

http://java.sun.com/javase/6/docs/api/java/lang/Math.html

Hands-on Exercise

Integer Operations

Exercise: Integer Operations

• Create a Java class named IntOpsin the Java101 project that performs integer operations on a pair of integers from the command line and prints the results.

Solution: Integer Operations

Boolean Data Type

• Useful to control logic and flow of a program.

Data Type Attributes

Values true or false

Typical literals true false

Operation and or not

Operator && || !

Logical operators

& (AND) | (OR)^

(EXCLUSIVE OR)

True False True False True False

True True False True True False True

False False False True False True False

Logical operators• & (AND): Only TRUE if both operands are TRUE

• | (OR): Only FALSE if both operands are FALSE

• ^ (EXCLUSIVE OR): Only TRUE if both operands are DIFFERENT

Conditional & Negation operatorsa !a a b a && b a || b

True False False False False False

False True False True False True

True false False True

True True true True

Boolean Comparisons

• Take operands of one type and produce an operand of type boolean.

operation meaning true false

== equals 2 == 2 2 == 3

!= Not equals 3 != 2 2 != 2

< Less than 2 < 13 2 < 2

<= Less than or equal 2 <= 2 3 <= 2

> Greater than 13 > 2 2 > 13

>= Greater than or equal

3 >= 2 2 >= 3

Type Conversion

• Convert from one type of data to another. • Implicit – no loss of precision– with strings

• Explicit: – cast – method.

Type Conversion Examplesexpression Expression type Expression value

“1234” + 99 String “123499”

Integer.parseInt(“123”) int 123

(int) 2.71828 int 2

Math.round(2.71828) long 3

(int) Math.round(2.71828) int 3

(int) Math.round(3.14159) int 3

11 * 0.3 double 3.3

(int) 11 * 0.3 double 3.3

11 * (int) 0.3 int 0

(int) (11 * 0.3) int 3

Hands-on Exercise

Leap Year Finder

Exercise: Leap Year Finder

• A year is a leap year if it is either divisible by 400 or divisible by 4 but not 100.

• Write a java class named LeapYear in the Java101 project that takes a numeric year as command line argument and prints true if it’s a leap year and false if not

Solution: Leap Year Finder

Data Types Summary• A data type is a set of values and operations on those values.

– String for text processing– double, int for mathematical calculation– boolean for decision making

• In Java, you must: – Declare type of values. – Convert between types when necessary

• Why do we need types? – Type conversion must be done at some level. – Compiler can help do it correctly. – Example: in 1996, Ariane 5 rocket exploded after takeoff because of

bad type conversion.

Introduction to Java

Conditionals and Loops

Conditionals and Loops

• Sequence of statements that are actually executed in a program.

• Enable us to choreograph control flow.

Conditionals• The if statement is a common branching structure. – Evaluate a boolean expression. • If true, execute some statements. • If false, execute other statements.

If Statement Example

More If Statement Examples

While Loop

• A common repetition structure. – Evaluate a boolean expression. – If true, execute some statements. – Repeat.

For Loop• Another common repetition structure. – Execute initialization statement. – Evaluate a boolean expression. • If true, execute some statements.

– And then the increment statement. – Repeat.

Anatomy of a For Loop

Loop Examples

For Loop

Hands-on Exercise

Powers of Two

Exercise: Powers of Two• Create a new Java project in Eclipse named Pow2• Write a java class named PowerOfTwo to print powers of 2 that are <= 2N

where N is a number passed as an argument to the program.– Increment i from 0 to N. – Double v each time

Solution: Power of 2

Control Flow Summary• Sequence of statements that are actually executed in a

program. • Conditionals and loops enable us to choreograph the

control flow. Control flow Description Example

Straight line programs

all statements are executed in the order given

Conditionals certain statements are executed depending on the values of certain variables

IfIf-else

Loops certain statements are executed repeatedly until certain conditions are met

while for

do-while

Homework Exercises

Java 101: Introduction to Java

Hands-on Exercise

Random Number Generator

Exercise: Random Number Generator• Write a java class named RandomInt to generate a pseudo-

random number between 0 and N-1 where N is a number passed as an argument to the program

Solution: Random Number Generator

Hands-on Exercise

Array of Days

Exercise: Array of Days

• Create a java class named DayPrinter that prints out names of the days in a week from an array using a for-loop.

Solution: Arrays of Days

public class DayPrinter {public static void main(String[] args) {

//initialize the array with the names of days of the week

String[] daysOfTheWeek =

{"Sunday","Monday","Tuesday","Wednesday",

"Thuesday","Friday”,"Saturday"};

//loop through the array and print their elements to //stdout

for (int i= 0;i < daysOfTheWeek.length;i++ ){System.out.println(daysOfTheWeek[i]);

}}

}

% javac DayPrinter.java

% java DayPrinterSundayMondayTuesdayWednesdayThuesdayFridaySaturday

Hands-on Exercise

Print Personal Details

Exercise: Print Personal Details

• Write a program that will print your name and address to the console, for example:

Alex Johnson23 Main StreetNew York, NY 10001 USA

Hands-on Exercise

Sales Discount

Exercise: Sales Discount• Create a new project in Eclipse named Sale • Create, compile, and run the FriendsAndFamily class as illustrated below • Debug this program in your IDE to find out how it works

Further Reading• Java Tutorials - https://docs.oracle.com/javase/tutorial/ • Java Language Basics -

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/index.html • Eclipse IDE Workbench User Guide - http://help.eclipse.org/kepler/

index.jsp • Intelli J IDE User Guide - https://www.jetbrains.com/idea/documentation/• Eclipse Tutorial - http://www.vogella.com/tutorials/Eclipse/article.html