lesson 1-introduction

Introduction

The Java Programming

Language

Java Development

Environment

Software Installation

Compilation Process

How to Compile and

Run a Java Application

How to Compile and

Run a Java Applet

The Java Programming

Language

Objects

Reusable software

components that

model real-world

items

Look all around you

People, animals,

plants, cars, etc.

Attributes

Size, shape, color,

weight, etc.

Behaviors (Methods)

Cars: forward,

backward, turn, etc.

Object-Oriented

Programming

Object-oriented design

(OOD)

Models real-world

objects

Models communication

among objects

Encapsulates data

(attributes) and

functions (behaviors)

Information hiding

Communication

through well-defined

interfaces

Object-oriented

language

Programming is called

object-oriented

programming (OOP)

Java Programming

Languages

Classes are a

fundamental concept in

Java.

It role is as ‘factories’

for objects.

An object is an entity

that can be

manipulated in a

program.

All program

statements are placed

inside methods

(functions or

procedures).

A method is a

collection of

programming

instructions for a

particular task.

Java Class

Java Environment

Java programs

normally undergo five

phases

Edit

Programmer writes

program and stores

program on disk with

extension .java

Compile

Compiler creates

bytecodes from

program and

store a program in a

file with

extension .class

Load

Class loader stores

bytecodes in memory

Execute (Interpret)

Interpreter translates

bytecodes into

machine language

Software Installation

Install Java 2 SDK

Compiler : j2sdk1_4_2-

win.exe

Documentation:

j2sdk1_4_2-doc.zip

Edit Autoexec.bat

SET PATH=c:

\jdk1.4.2\bin;%PATH%

SET CLASSPATH= .;c:

\working_directory

Compilation Process

**Figure from

java.sun.com

How to Compile and

Run a Java Application

Edit-Compile-Debug

Loop

1. To Edit :

- use any text editor such

as Notepad

- save source code with

extension .java

2. To Compile : use the

command

javac Hello.java

if no error, a file names

“Hello.class” is created

3. To Run : use command

java Hello

(java virtual machine)

Java Syntax

1.1 Simple Program

public class ClassName

{ public static void main

(String[] args)

{ statements

}

}

1.2 Method Call

object.methodName

(parameters)

Example:

System.out.println(“Hi”);

A Simple Java

Application

1. // Example 1 : Hello

Application

2. // Hello.java

3.

4. public class Hello {

5. public static void

main(String args[]) {

6. System.out.println

(“Hello!”);

7. }

8. }

Java

Java is case-sensitive.

On line 4, the keyword

“public” indicates that

the class

is usable by the

“public”

The name of the public

class must be the

same as the file name

Line 5 defines a

method called main

String[ ] args is a

parameter that

contains the command

line arguments

Every statement must

end with a semicolon

Method in a particular

object can be called by

class.object.method

For example:

System.out.println

System.out.println

(“Hello”) statement

calls method println of

object names

System.out that prints

“Hello”

“Hello” is a string

which is enclosed

insidedouble quotation

marks

System.out.println(5 +

4); // 9

9

System.out.println(“5 +

4”); // 5 + 4

5 + 4

System.out.print

(“Hello”);

System.out.println

(“Java”);

HelloJava

Escape Sequences

To print

Hello "Java"

Can’t use

System.out.println

("Hello "Java"");

Must use escape

sequence (\)

System.out.println

("Hello \"Java\"");

System.out.println("c:\

\data\\a.txt"); will print

c:\data\a.txt

\n starts a new line, for

example:

System.out.print(“A\nB

\nC”); will print

A

B

C

\t moves the screen

cursor to the next tab

stop

\r positions the cursor

to the beginning of the

current line

Import

To use classes from

Java Class Library, we

need to import those

classes from a

package in the library.

import packageName.

Classname;

Package is a collection

of classes with a

related purpose.

For example:

import

java.applet.applet;

A Simple Java Applet

// Example 2: HelloApplet

import

java.applet.Applet;

import

java.awt.Graphics;

public class

HelloApplet extends

Applet {

public void paint

(Graphics g) {

g.drawString(“Hello !”,

25, 25);

}

}

How to Compile and

Run a Java Applet

To Compile

c:> javac HelloApplet.java

To Run an applet, we

need HelloApplet.html



code=”HelloApplet.
class” width=500
height=300



Then, To run this

applet,

c:> appletviewer

HelloApplet.html

or use any browsers, e.g.

Netscape, Internet

Explorer.