Applet

Major Applet Activities

Applets have many different activities that correspond to various major events in the life cycle of the applet-for example,

1. initialization,

2. painting,

3. and mouse events.

Each activity has a corresponding method, so when an event occurs, the browser or other Java-enabled tool calls those specific methods.

There are five of the most important methods in an applet's execution:

1. initialization,

2. starting,

3. stopping,

4. destroying,

5. and painting.

Initialization

Initialization occurs when the applet is first loaded (or reloaded), similarly to the main() method in applications. The initialization of an applet might include reading and parsing any parameters to the applet, creating any helper objects it needs, setting up an initial state, or loading images or fonts.

To provide behavior for the initialization of our applet, override the init() method in our applet class:

public void init()
{
...
} Starting

After an applet is initialized, it is started. Starting is different from initialization because it can happen many different times during an applet's lifetime, whereas initialization happens only once. Starting can also occur if the applet was previously stopped.

For example,

An applet is stopped if the reader follows a link to a different page, and it is started again when the reader returns to this page.

To provide startup behavior for your applet, override the start() method:

public void start()
{
...
} Stopping

Stopping

Stopping occurs when the reader leaves the page that contains a currently running applet, or you can stop the applet yourself by calling stop(). By default, when the reader leaves a page, any threads the applet had s tarted will continue running.

By overriding stop(), you can suspend execution of these threads and then restart them if the applet is viewed again:

public void stop()
{
...
}

Destroying

Destroying enables the applet to clean up after itself just before it is freed or the browser exits-for example, to stop and remove any running threads, close any open network connections, or release any other running objects. Generally, we won't want to override destroy() unless we have specific resources that need to be released-for example, threads that the applet has created.

To provide clean-up behavior for your applet, override the destroy() method:

public void destroy()
{
...
}

Painting

Painting is how an applet actually draws something on the screen, be it text, a line, a colored background, or an image. Painting can occur many thousands of times during an applet's life . We override the paint() method if your applet needs to have an actual appearance on the screen (that is, most of the time).

The paint() method looks like this:

public void paint(Graphics g)
{
...
}

paint() takes an argument, an instance of the class Graphics. This object is created and passed to paint by the browser,

import java.awt.Graphics;

A Simple Applet
The Hello Again applet

import java.awt.Graphics;

import java.awt.Font;
import java.awt.Color;
public class Aman extends java.applet.Applet
{
Font f = new Font("TimesRoman", Font.BOLD, 36);
public void paint(Graphics g)
{
g.setFont(f);
g.setColor(Color.red);
g.drawString("Hello again!", 5, 40);
}
}

Output

This applet implements the paint() method, one of the major methods described in the previous section (actually, it overrides the default implementation of paint(), which does nothing). Because the applet doesn't actually do much (all it does is print a couple words to the screen), and there's not really anything to initialize, you don't need a start(), stop(), init(), or destroy() method.