Java applet

JAVA
Applet class
Prepared by
Miss. Arati A. Gadgil

Applet
An applet is a Java program that runs in a Web browser. An
applet can be a fully functional Java application because it has
the entire Java API at its disposal.
•An applet is a Java class that extends the java.applet.Applet
class.
•A main() method is not invoked on an applet, and an applet
class will not define main().
•Applets are designed to be embedded within an HTML page.
When a user views an HTML page that contains an applet, the
code for the applet is downloaded to the user's machine. 2

•A JVM is required to view an applet. The JVM can be either
a plug-in of the Web browser or a separate runtime
environment.
The JVM on the user's machine creates an instance of the
applet class and invokes various methods during the applet's
lifetime.
•Applets have strict security rules that are enforced by the
Web browser. The security of an applet is often referred to as
sandbox security, comparing the applet to a child playing in a
sandbox with various rules that must be followed.
•Other classes that the applet needs can be downloaded in a
single Java Archive (JAR) file 3

Life Cycle of an Applet
1.init: This method is intended for whatever initialization is
needed for your applet. It is called after the param tags inside
the applet tag have been processed.
2.start: This method is automatically called after the browser
calls the init method. It is also called whenever the user returns
to the page containing the applet after having gone off to other
pages.
3.stop: This method is automatically called when the user
moves off the page on which the applet sits. It can, therefore,
be called repeatedly in the same applet.
4

3. destroy: This method is only called when the browser
shuts down normally. Because applets are meant to live on
an HTML page, you should not normally leave resources
behind after a user leaves the page that contains the applet.
4. paint: Invoked immediately after the start() method, and
also any time the applet needs to repaint itself in the
browser. The paint() method is actually inherited from the
java.awt
5

java.applet.Applet class
For creating any applet java.applet.Applet class must be
inherited. It provides 4 life cycle methods of applet.
public void init(): is used to initialized the Applet. It is
invoked only once.
public void start(): is invoked after the init() method or
browser is maximized. It is used to start the Applet.
public void stop(): is used to stop the Applet. It is invoked
when Applet is stop or browser is minimized.
public void destroy(): is used to destroy the Applet. It is
invoked only once. 6

java.awt.Component class
The Component class provides 1 life cycle method of applet.
public void paint(Graphics g):
Is used to paint the Applet. It provides Graphics class
object that can be used for drawing oval, rectangle, arc etc.
7

How to run an Applet?
There are two ways to run an applet
1.By html file.
2.By appletViewer tool (for testing purpose).
8

import java.applet.Applet;
import java.awt.Graphics;
public class First extends Applet
{
public void paint(Graphics g)
{
g.drawString("welcome to applet",150,150);
}
}
/*
<applet code="First.class" width="300" height="300">
</applet>
*/
9

<html>
<body>
<applet code="First.class" width="300" height="300">
</applet>
</body>
</html>
10

11
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
/*
<applet code=applet1.class
width=400
height=400>
</applet>
*/
public class applet1 extends Applet
{
public void init()
{
addMouseListener(new MouseAdapter()
{

12
public void mouseClicked(MouseEvent e)
{
x=e.getX();
y=e.getY();
repaint();
}
});
}
int x,y;
public void paint(Graphics g)
{
g.drawString("Welcome",x,y);
}
}

Java applet

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