java lecture1 introduction

8/6/2019 Java Lecture1 Introduction

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Object Oriented Programmingwith

JAVA

References:Java JDK6 documentations. http://java.sun.com/javase/

Java How to Program, Sixth Edition

Instructor: Haya Sammaneh


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History of Java

Java

Originally for intelligent consumer-electronic

devices (cell phones)

Then used for creating Web pages with dynamic

content

Now also used for:

Develop large-scale enterprise applications


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The Java Programming Language

A high-level language that can be characterized by all of thefollowing:

Simple Object oriented

Portable

Distributed

High performance

Multithreaded

Robust

Secure


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Java life cycle Java programs normally undergo four phases

Edit

Programmerwritesprogram (and stores program on

disk)

Compile Compiler creates bytecodes from program (.class)

Load

Class loaderstores bytecodes in memory

Execute

Interpreter: translates bytecodes into machine language


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Java life cycle

Source code (.java)

Compiled into Byte codes (.class) , as (.exe) in c++

The Java Application Programming Interface

(API)

a large collection of ready-made software components. It isgrouped into libraries of related classes and interfaces;these libraries are known aspackages.

Java Virtual Machine (JVM)

Machine code


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Java life, cont..


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JVM an Portability Through the Java VM, the same application is

capable ofrunning on multiple platforms.


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Java Technology

Java EE vs.

Java SE

EE: enterprise edition (web services, distribution, RMI, )

SE: standard edition (stand alone app.)

D

evelopment Tools The main tools you'll be using are thejavac compiler, thejava launcher (java), and thejavadoc documentation tool.

Application Programming Interface (API)

Java SE Development Kit 6 (JDK 6)

Offers a wide array of useful classes ready for use in yourown applications.


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Java Technology, cont

UserInterface Toolkits

Swing and Java 2D toolkits to create GraphicalUserInterfaces (GUIs).

Integration Libraries

Application Programming Interface (API)

Java RMI, and Java Remote Method InvocationoverInternet Inter-ORB Protocol Technology(Java RMI-IIOP Technology) enable databaseaccess.


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Before you startInstall the Java SE Development

Kit 6 (JDK 6).

Modify the Java Path environment. Go to the System Properties by right

clicking you My Computer andchoosing properties Environmentvariablesclick on TEMP Edit.

Add the path to the javabin directory asshown in the next slid.

Install the Textpad editorwhichwe will use to develop ourapplications.


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Modifying the Path Environment variable.


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Hello world

To begin you need a text editor. Notepad, TextPad,

Create a new directory on C: name it JavaProjects.

Open new file, save it as HelloWorld.java in new directoryHelloWorld inside the JavaProjects Directory.

Write the following code and save the file:

class HelloWorld {

/*simple java application*/

public static void main(String[] args) {

System.out.println(Hello World); //displays a string }

}

Note: the file name should have the same name as the class


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Compiling and running Assuming the HelloWorld.java is saved in the c:\JavaProjects\HelloWorld

directory:

Open the a Console, (startRun), type cmd.

Type cd \ to return to c:>

Go to the helloworld directry (cd c:\JavaProjects\HelloWorld)

compile your application

javac HelloWorld.java

Run your application

java HelloWorld.class

Note: Type all code, commands, and file names exactly as shown. Both the

compiler (javac) and launcher (java) are case-sensitive


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Closer Look Three primary components: source code comments, the

HelloWorld class definition, and the main method.

Comments are ignored by the compiler but are useful to otherprogrammers.

Two supported kinds of comments

/* text */ The compiler ignores everything from /* to */.

// text The compiler ignores everything from // to the end of the

line.

The most basic form of a class definition is

class name {}

Every program must have at least one class, and this class shouldcontain the main method.


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Closer Look, cont

In the Java programming language, every application mustcontain a main method whose signature is:

public static void main(String[] args)

The modifiers public and static can be written in either order(publicstatic or static public).

You can name the argument anything you want, but most programmers

choose "args" or "argv.

This is the string array that will contains the command linearrguments.

The main method is the entry point for your application and will

subsequently invoke all the other methods required by your program.

System.out.println("Hello World!");

uses the System class from the API to print the "Hello World!" messageto standard output.


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Example, Prints.java

import java.lang.System;

class Prints

{

public static void main(String[] args)

{System.out.print(":Haya ");

System.out.println("This Text in one line");

System.out.printf("\nFormatedtext;\n%s\t%s\n%s\t%d\n%s\t%d\n","Student","Mark","Ahmad",3,"Sami",5);

System.out.printf(" %x\n",15); // f

System.out.printf(" %o\n",15); // 17

}

}

%o for octal, %x for hexadicemal, %f for floating point representations.


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Example

Name of class called identifier

Series of characters consisting of letters, digits,underscores ( _ ) and dollar signs ( $ )

Does not begin with a digit, has no spaces

Java is case sensitive

Examples: Print, $Print, _Print, Print7 is valid

7print is invalid


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Summation of two numbers

Exampleimport java.util.Scanner; // program uses class Scanner

public class Summation

{

public static void main( String args[] )

{

// create Scanner to obtain input from command window

Scanner input = new Scanner(System.in );

int number1;

int number2;

int sum;

System.out.print( "Enter first integer: " );

number1 = input.nextInt(); // read first number from user

System.out.print( "Enter second integer: " );number2 = input.nextInt(); // read second number from user

sum = number1 + number2; // add numbers

System.out.printf( "Sum is %d\n", sum ); // display sum


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Summation cont. import: used to get the library (Java API) contains the definition for the used

classes

We need the scanner class defined in java.util.scanner package

All imports must be at the beginning, before class definition.

Using a Java APIwithout importing the required package cause syntax

error.

A Scanner enables a program to read data (e.g., numbers). The data cancome from many sources, such as a file on disk or the user at thekeyboard (System.in).

By default, packagejava.lang is imported in every Java program, thispackage contains the definition for System class.

We uses Scanner object input's nextInt method to obtain an integerfrom the user at the keyboard.


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Object-Oriented ProgrammingConcepts

What Is an Object?

What Is a Class? What Is Inheritance?

What Is an Interface?

What Is a Package?


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What Is an Object?

Real world consists ofobjects (desk, your television set, yourbicycle).

They share two characteristics: They all have state and behavior.

Bicycles have state (current gear, current speed) and behavior(changing gear, applying brakes).

Hiding internal state and requiring all interaction to be performedthrough an object's methods is known as data encapsulation.


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What Is an Object? cont.

Grouping code into individual software objects provides a number ofbenefits, including:

Modularity: The source code for an object can be written andmaintained independently of the source code for other objects. Oncecreated, an object can be easily passed around inside the system.

Information-hiding: By interacting only with an object's methods, thedetails of its internal implementation remain hidden from the outsideworld.

Code re-use: If an object already exists , you can use that object in

your program.

Pluggability and debugging ease: If a particular object turns out to beproblematic, you can simply remove it from your application andplug in a different object as its


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What Is a Class?

In object-oriented terms, we say that yourbicycle is aninstance of the class of objects known as bicycles.

class Bicycle {

int speed = 0;int gear = 1;

void changeGear(int newValue) { gear = newValue; }

void speedUp(int increment) { speed = speed + increment; }

void applyBrakes(int decrement) { speed = speed - decrement; }

void printStates() { System.out.println( speed:"+speed+"gear:"+gear); }

}


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What Is a Class? cont. Here's a BicycleDemo class that creates two separate Bicycle objects

and invokes theirmethods:

class BicycleDemo {public static void main(String[] args) {// Create two different Bicycle objectsBicycle bike1 = new Bicycle();

Bicycle bike2 = new Bicycle();// Invoke methods on those objectsbike1.speedUp(10);bike1.changeGear(2);bike1.printStates();

bike2.speedUp(10);bike2.changeGear(2);bike2.speedUp(10);bike2.changeGear(3);bike2.printStates();}

}


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What Is Inheritance?

Object-oriented programming allows classes to inherit commonly usedstate and behavior from other classes.

The syntax for creating a subclass is simple. At the beginning of your

class declaration, use the extends keyword, followed by the name ofthe class to inherit from:

class MountainBike extends Bicycle{// new fields and methods defining a mountain bike

// would go here}


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What Is an Interface? An interface is a group of related methods with empty bodies.

interface Bicycle{

void changeGear(int newValue);void speedUp(int increment);void applyBrakes(int decrement);

}

To implement this interface, the name of your class would change (toACMEBicycle, for example), and you'd use the implements keywordin the class declaration:

class ACMEBicycle implements Bicycle{// remainder of this class implemented as before}


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What Is a Package?

A package is a namespace that organizes

a set ofrelated classes and interfaces.

you can think of packages as being similar

to different folders on your computer.


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Language Basics

Variables

Operators

Expressions, Statements, and Blocks Control Flow Statements


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Variables

Four kinds:

Instance Variables (Non-Static Fields). Values are unique to each instance (object) of a class

Class Variables (Static Fields). There is exactly one copy of this variable in existence.

Local Variables.

Parameters.


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Variables Naming

Variable names are case sensitive.

Can be any legal identifier an unlimited-length sequenceof Unicode letters and digits, beginning with a letter, thedollar sign, "$", or the underscore character, "_".

If the name you choose consists of only one word, spell

that word in all lowercase letters. If it consists ofmorethan one word, capitalize the first letter of eachsubsequent word. Ex: GearRatio


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Variables - Primitive Data Types

byte: 8-bit signed integer.

short : 16-bit signed integer int: 32-bit signed integer

long: 64-bit signed integer


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Variables - Primitive Data Types

float: 32-bit This data type should never be used for precise values, such as

currency. For that, you will need to use thejava.math.BigDecimalclass instead.

double: 64-bit

boolean: has only two possible values: true and false.

char:The char data type is a single 16-bit Unicode character. ('\u0000'(or 0) to '\uffff' (or65,535).

String object; for example, String s = "this is a string";.Once created, their values cannot be changed.


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Literals Ex:

boolean result = true;char capitalC = 'C' ;byte b = 100;short s =10000;int i = 100000;

int: int decVal = 26; // The number 26, in decimal int hexVal = 0x1a; // The number 26, in hexadecimal

float and double: E or e (for scientific notation)

F or f (32-bit float literal) D or d (64-bit double literal). double d1 = 123.4; double d2 = 1.234e2; // same value as d1, but in scientific notation float f1 = 123.4f;


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Literals cont.

char and String:

char ch='\u0108;


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Arrays

An array is a containerobject. Each item in an array is called an element, and each element is

accessed by its numerical index.

Declaring a Variable to Refer to an Array

type[] ; Ex: int[] arrayOfIntegers; float arrayOfFloats[ ]; // this form is discouraged

Creating, Initializing, and Accessing an Array =new type[]; Ex: arrayOfIntegers = new int[10]; // create an array of integers Or you can create and initialize at the same time: int[] anArray = {100, 200, 300, 400, 500, 600, 700, 800, 900, 1000};


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Multidimensional Arrays

int b[][] = { { 1, 2 }, { 3, 4, 5 } };

int b[][];

b = new int [ 3 ][ 4 ];

int b[][];

b = new int[ 2 ][ ]; // create 2 rows

b[ 0 ] = new int[ 5 ]; // create 5 columns for row 0b[ 1 ] = new int[ 3 ]; // create 3 columns for row 1


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Operator


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Operators cont.

The + operatorcan also be used for concatenating (joining) twostrings together, as shown in the following ConcatDemo

class ConcatDemo

{public static void main(String[] args){String firstString = "This is";String secondString = " a concatenated string.";String thirdString = firstString+secondString;

System.out.println(thirdString);}

}


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Expressions, Statements, and Blocks

An expression is a construct made up of variables, operators, and

method invocations.1 * 2 * 3x + y / 100 // ambiguous(x + y) / 100 // unambiguous, recommendedx + (y / 100) // unambiguous, recommended

A statement forms a complete unit of execution.aValue = 8933.234; // assignment statementaValue++; // increment statementSystem.out.println("Hello World!"); // method invocation // statementBicycle myBike = new Bicycle(); // object creation // statement


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Expressions, Statements, and Blocks

A block is a group of zero or more statements between balancedbraces and can be used anywhere a single statement is allowed.

class BlockDemo {

public static void main(String[] args) {boolean condition = true;

if (condition) { // begin block 1System.out.println("Condition is true."); } // end block oneelse { // begin block 2

System.out.println("Condition is false.");} // end block 2}}


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Control Flow Statements

Decision-making statements

if, if-else, switch

The looping statements

for, while, do while

The branching statements

break, continue, return


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Decision-making statements .void applyBrakes(){

if (isMoving){ // the "if" clause: bicycle must be movingcurrentSpeed--; // the "then" clause: // decrease current speed}} The opening and closing braces are optional, provided that the

"then" clause contains only one statementvoid applyBrakes(){if (isMoving) {currentSpeed--;}else {

System.err.println("The bicycle has already stopped!");}

}


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The while and do-while Statements Ex1:

class WhileDemo {public static void main(String[] args){int count = 1;while (count < 11) {System.out.println("Count is: " + count); count++;}

}} Ex2:class DoWhileDemo {

public static void main(String[] args){int count = 1;do { System.out.println("Count is: " + count); count++; } while (count


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The for Statement and continue.

class PsDemo {public static void main(String[] args) {String searchMe = "peter piper picked a peck of " + "pickled

peppers";int max = searchMe.length();

int numPs = 0;for (int i = 0; i < max; i++) { //interested only in p'sif (searchMe.charAt(i) != 'p')continue; //process p'snumPs++;

}System.out.println("Found " + numPs + " p's in the string.");}

}


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The for statement and break.class BreakDemo {

public static void main(String[] args) {int[ ] arrayOfInts = { 32, 87, 3, 589, 12, 1076, 2000, 8, 622, 127 };

int searchfor = 12;

int i;

boolean foundIt = false;

for (i = 0; i < arrayOfInts.length; i++) {

if (arrayOfInts[i] == searchfor) {

foundIt = true;break; //


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continue and break with lableclass BreakWithLabelDemo {

public static void main(String[] args) {

int[][] arrayOfInts = { { 32, 87, 3, 589 }, { 12, 1076, 2000, 8 }, { 622, 127, 77, 955 }};

int searchfor = 12;

int i;

int j = 0;

boolean foundIt = false;

search: //

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