Applet

The life cycle of a Web page applet

The processing of all Web page applets is as follows:

1. The applet's init() method is automatically called when the page containing the applet is loaded by the browser or applet viewer. Its purpose is to perform applet initialization and it is called only once during the life of the applet. For a simple applet, this is the only required method. An applet does not need a main() method. If one exists, it is ignored.

2. The applet's start() method is automatically called after init() and every time the page is revisited. Its purpose is to resume suspended applet processing when the user returns to the page after surfing.

3. The applet's stop() method is automatically called when the user surfs to another page or when the browser is being shut down. Its purpose is to suspend applet processing.

4. The applet's destroy() method is automatically called after stop() when the browser or applet viewer is being shut down. Its purpose is to release all applet resources and it is called only once during the life of the applet.

A sample applet

The following statements define a small applet that displays a message when the user clicks a button. The button may then be re-clicked to clear the message:

import java.awt.*;
import java.awt.event.*;
import java.applet.*;

public class Aman extends Applet implements ActionListener
{

Button b = new Button("Show message");
TextField message = new TextField("", 15);

public void init()
{
resize(300, 100);
setBackground(Color.lightGray);
b.addActionListener(this);
add(b);
message.setFont(new Font("Serif", Font.ITALIC, 24));
message.setForeground(Color.red);
message.setEditable(false);
add(message);
}

public void actionPerformed(ActionEvent e)
{
if (message.getText().length() == 0)
{
message.setText("Hello world!");
b.setLabel("Clear message");
}
else {
message.setText("");
b.setLabel("Show message");
}
}
}

Notes:

1. By importing the java.applet package, accessing the Applet class is made easier

2. The applet needs no WindowListener interface because it isn't a window

3. Processing begins with the init() method. It immediately resizes the window to override any size specified by the applet's HTML tag .Everything else about the applet is virtually the same as we would see in an equivalent windows program (with the exception of window event handling which isn't needed).

4. NOTE: The procedure for compiling a Java applet is identical to the procedure for compiling a Java program. To test the applet's bytecode, however,we must launch the applet viewer program. This is done by entering the command: appletviewer App.php