Java applet

Java Applet Programming
Rohan K. Gajre.

Outline
• Introduction to java Programming
• Applet Overview
• Applet Skeleton
• Steps to Write Applet Code
• Compilation Process
• Java Applet E.g. with HTML Code

What is Java
• Java is Simplified version of C++
• Java is a programming language that is object Oriented and specifically
designed to have as few implementation dependencies as possible
• Java Programs can be easily moved form one computer to another
• Almost everything in Java is an Object and Classes
• Java has the ability to share both data and program
• Java does not use pointer and header files
• A class is collection of Object of similar type

What is Applet
• Applet are Java Program that are used for Internet Computing
• Applet can be transported over the internet from one computer to
another
• It can perform logical and arithmetic operations as well as accept user
input
• Applet are event driven
• If you want to write applet code so you need to import two packages
that is awt(Abstract Window Toolkit) and applet

Cont.
• Execution of applet code does not begin with main()function
• Types of Applet
Local Applet :- Developed & stored in Local System
Remote Applet :- Developed & stored on a Remote computer
connected to the internet
• Once an applet has been compiled, it is included in an HTML file
using Applet tag

Cont.
• Applets are not executed by a console based java run-time interpreter,
but they are executed by either a java enabled web browser or an
applet viewer.
• You need two notepad one for java(Applet)code and another for
HTML code having Applet Tag in that

An Applet Skeleton
• Applet skeleton includes different methods for writing applet
• When an applet begins, the AWT calls the following methods, in this
sequence:
init( )
start( )
paint( )
• When an applet is terminated, the following sequence of method calls
takes place:

Cont.
• stop( )
• destroy( )
• Above all methods are in Applet Life cycle
• Explanation about above is as follows:
• init( ):- init() is the first method to be called. This is where you should
initialize variables. This method is called only once during run time of
your applet

Cont.
• start( ):- start() called after init(), also called to restart applet after it
has been stopped. start() is called each time an applet’s HTML
document is displayed on screen.
• paint( ):- paint() is called each time your applets output must be
redrawn. also called when the applet begins execution. This method
has one parameter, Graphics.
• stop( ):- stop()is called when a web browser leaves the HTML
document containing the applet- when it goes to another page.

Cont.
• destroy( ) :- destroy() is called when environment determines that
your applet needs to be removed completely from memory. The stop()
method is always called before destroy().

Steps to write Applet code
• Writing an applet code in java file & save with class name (.java file)
• Compile it & create (.class file)
• Design a page using HTML tags
• Write a <APPLET> Tag in that
• Save it same as a class name with .HTML extension
• Testing

Compilation Process
• Open command prompt then go to directory using CD command
• E.g. c:Users>d:
• I am in D Drive now going to my directory using CD command
• D:> cd Ram
• I am in my directory that is Ram
• Compile source file D:Ram> Javac Classname.java
• E.g. D:Ram> Javac Demo.java

Cont.
• Open file in appletviewer
• Then Run HTML code
• D:Ram> appletviewer classname.html
• E.g. D:Ram> appletviewer Demo.html

Following Program shows a simple java
applet
import java.applet.*;
import java.awt.*;
public class DemoApp extends Applet{
public void paint (Graphics g) {
g.drawString (“Welcome in Applet World", 25, 50);
}
}

Cont.
• Save source file with name DemoApp.java
• Compile source file D:Ram> javac DemoApp.java
• Write HTML File and save it DemoApp.html

HTML Code
<html>
<title> Welcome in Applet World </title>
<hr>
<applet code=“DemoApp.class" width="320" height="120">
</applet>
</hr>
</html>

Cont.
• Open file in appletviewer
• Then Run HTML code
• D:Ram> appletviewer DemoApp.html

Java applet

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