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Writing applets

}

var oApplet = getApplet(“ExampleApplet”);

After you have a reference to the applet, you can actually access all the applet’s public methods directly

from JavaScript, such as:

oApplet.appletPublicMethod();

This opens up all kinds of functionality to JavaScript by using a Java applet as a host environment;

JavaScript can control anything that can be done within the applet.

Writing applets

To write a Java applet, you must first download the Java Development Kit (JDK) from Sun’s Web site

(

http://java.sun.com/j2se/

). It is up to you whether you use a development environment or a

plain text editor to write the applet, but all applets have one thing in common: they must inherit from

java.applet.Applet

. (You can, however, create a Swing-based Java applet by inheriting from

javax.swing.JApplet

, which inherits from

java.applet.Applet

Here’s a small example applet:

import java.applet.Applet;

import java.awt.Graphics;

import java.awt.HeadlessException;

public class ExampleApplet extends Applet {

private String message = “Hello World!”;

public ExampleApplet() throws HeadlessException {

super();

}

public void paint(Graphics g) {

g.drawString(message, 20, 20);

}

public void setMessage(String message) {

this.message = message;

repaint();

}

This applet simply displays the text

“Hello World!”

on the applet. The

paint()

method controls

what is displayed when the applet is first loaded, and it receives a

Graphics

object as its sole argument.

The

Graphics

object is a representation of the visual area of the applet with methods to draw onto the

applet, such as

drawString()

, which draws the given text at the x and y coordinates specified.

The applet defined previously also has a private property called

message

, which is initialized to

“Hello

World!”

This property can be changed by calling

setMessage()

, which is accessible from JavaScript

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