The Lifecycle of a Java Applet

In the early days of the web, Java applets reigned supreme, bringing animation, interaction, and a breath of life to static web pages. But just like any program, applets have a distinct lifecycle – a series of stages they go through from creation to termination. Let's embark on a journey to explore the fascinating lifecycle of a Java applet!

The Stages of an Applet's Life

Imagine an applet as a tiny actor on the web stage. Here's the script it follows:

1. Initialization (init()): This is the grand entrance! When a web page containing an applet is loaded, the browser first downloads the applet code. Once downloaded, the init() method is called, signifying the applet's birth. Here, the applet can perform essential setup tasks like initializing variables, loading resources (images, sounds), and potentially establishing connections to external services.

2. Start (start()): The curtain rises! After initialization, the start() method is invoked. This signals that the applet is ready to take center stage and begin its execution. Animations might start playing, user interaction might become active, and the applet becomes a fully functioning part of the web page.

3. Run: This is the heart of the show! Once started, the applet enters a continuous loop where its core functionalities come alive. This could involve processing user input, updating graphics, or interacting with the web page content. The applet remains in this "running" state until it's explicitly stopped or the web page is unloaded.

4. Stop (stop()): The intermission! If the user navigates away from the web page containing the applet, the browser calls the stop() method. This instructs the applet to pause its execution and release any resources it might be holding. The applet is essentially put on hold, but it can be restarted later if the user returns to the same page.

5. Destroy (destroy()): The final curtain call! When the web page is completely unloaded or the browser window is closed, the destroy() method is invoked. This is the applet's final act, where it performs any necessary cleanup tasks like saving data or releasing resources permanently. After this, the applet is removed from memory, and its existence comes to an end.

Behind the Scenes: The Applet Class

The lifecycle methods (init(), start(), stop(), and destroy()) are all defined within the java.applet.Applet class. When you create an applet class in your Java code, you inherit from this class, gaining access to these lifecycle methods and the functionalities they provide.

A Glimpse of Applet Code (Example)

Here's a simplified example demonstrating the usage of lifecycle methods:

Java

public class MyApplet extends Applet {

  private int count = 0;

  @Override
  public void init() {
    // Initialization tasks (e.g., setting background color)
  }

  @Override
  public void start() {
    // Start animation or other continuous tasks
  }

  @Override
  public void stop() {
    // Pause animation or other tasks
  }

  @Override
  public void destroy() {
    // Cleanup tasks
  }

  // Applet logic (e.g., handling user interaction)
}

In this example, the init(), start(), stop(), and destroy() methods are overridden to perform specific tasks at each stage of the applet's lifecycle. The core logic of the applet (like handling user interaction) would reside outside these methods.

Conclusion

Understanding the Java applet lifecycle is crucial for writing well-behaved applets. By effectively utilizing the lifecycle methods, you can ensure your applets initialize correctly, perform smoothly while running, and clean up after themselves when no longer needed. Though applets might not be the web stars they once were, appreciating their lifecycle offers valuable insights for any Java developer.