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Applet Life Cycle in Java

The Applet life cycle consists of a series of methods that are invoked sequentially during the execution of an applet. These methods provide a well-defined structure for initializing, starting, stopping, and destroying an applet. The life cycle is managed by the Java Virtual Machine (JVM) and is essential for applet-based applications.

Phases of the Applet Life Cycle

An applet’s life cycle consists of four key phases, each represented by a specific method:

  1. Initialization (init())
  2. Starting (start())
  3. Stopping (stop())
  4. Destruction (destroy())

In addition, the paint(Graphics g) method is used to render the applet’s content visually.

Applet Life Cycle Methods

1. init()

  • Purpose: Initializes the applet. Called only once when the applet is loaded into memory.
  • Usage: Used to allocate resources, initialize variables, and set up the user interface.
  • Example:

public void init() {

    System.out.println(“Applet initialized”);

    // Initialization logic

}

2. start()

  • Purpose: Starts or resumes the applet’s execution. Called after init() or when the applet becomes visible again.
  • Usage: Used to start animations, threads, or any activity that needs to run when the applet is active.
  • Example:

public void start() {

    System.out.println(“Applet started”);

    // Start or resume tasks

}

3. stop()

  • Purpose: Pauses the applet’s execution. Called when the applet is no longer visible (e.g., the user navigates away from the page).
  • Usage: Used to stop animations, threads, or background tasks.
  • Example:

public void stop() {

    System.out.println(“Applet stopped”);

    // Pause or stop tasks

}

4. destroy()

  • Purpose: Cleans up resources before the applet is removed from memory. Called once when the applet is terminated.
  • Usage: Used to release resources like threads, file handles, or network connections.
  • Example:

public void destroy() {

    System.out.println(“Applet destroyed”);

    // Cleanup logic

}

5. paint(Graphics g)

  • Purpose: Used to render the applet’s visual content. Called whenever the applet needs to redraw itself.
  • Usage: Typically used to display text, shapes, or images.
  • Example:

public void paint(Graphics g) {

    g.drawString(“Welcome to the Applet Life Cycle!”, 50, 50);

}

Applet Life Cycle Flow

  1. Loading the Applet:
    1. The applet is loaded, and the init() method is invoked to perform initialization.
  2. Starting the Applet:
    1. The start() method is called immediately after init() and whenever the applet becomes visible.
  3. Running the Applet:
    1. The applet can handle user interactions, execute threads, or render visual elements.
  4. Stopping the Applet:
    1. The stop() method is called when the user navigates away from the applet’s webpage.
  5. Destroying the Applet:
    1. The destroy() method is called when the applet is removed from memory, typically during browser shutdown or page unload.

Complete Example: Applet Life Cycle

import java.applet.Applet;

import java.awt.Graphics;

public class LifeCycleApplet extends Applet {

    // Called once when the applet is loaded

    public void init() {

        System.out.println(“init() called”);

    }

    // Called every time the applet starts

    public void start() {

        System.out.println(“start() called”);

    }

    // Called to draw the applet’s content

    public void paint(Graphics g) {

        g.drawString(“Applet Life Cycle Demo”, 50, 50);

        System.out.println(“paint() called”);

    }

    // Called when the applet is stopped

    public void stop() {

        System.out.println(“stop() called”);

    }

    // Called once before the applet is destroyed

    public void destroy() {

        System.out.println(“destroy() called”);

    }

}

HTML Code to Run the Applet

<html>

<body>

    <applet code=”LifeCycleApplet.class” width=”300″ height=”150″>

    </applet>

</body>

</html>

Execution Steps

  1. Compile the Applet:

javac LifeCycleApplet.java

  • Run with Applet Viewer:

appletviewer AppletLifeCycle.html

Applet Life Cycle Sequence

  1. init() is called once when the applet is loaded.
  2. start() is called immediately after init() and whenever the applet becomes active.
  3. paint(Graphics g) is called whenever the applet needs to be redrawn.
  4. stop() is called when the applet is no longer visible.
  5. destroy() is called when the applet is removed from memory.

Advantages of Applet Life Cycle

  • Provides a structured framework for applet execution.
  • Ensures proper resource allocation and cleanup.
  • Simplifies event handling through predefined methods.

Limitations

  • Modern browsers no longer support applets due to security concerns.
  • Applets require a Java plugin, which is obsolete in many environments.
  • Limited to the functionality provided by the browser’s Java environment.