Java Applets

In addition to being a powerful programming language for application development, Java also introduced the concept of Java applets. Java applets are small application programs that run within a web browser. They were widely used in the early days of the internet to add interactive content to websites. In this section, we will explore what Java applets are and how to create them.

What is a Java Applet?

A Java applet is a special type of Java program that is embedded in a web page and executed within a Java-compatible web browser. Applets are designed to provide dynamic and interactive content on web pages. They can be used to create games, animations, data visualizations, and more. Java applets are written in Java and compiled into bytecode, which can be interpreted and executed by the Java Virtual Machine (JVM) within the browser.

Applet Lifecycle

When a web page containing a Java applet is loaded, the browser downloads the applet's bytecode and executes it within a restricted environment known as the applet sandbox. The applet goes through a lifecycle consisting of several methods that are automatically invoked at different stages:

1. init()

The init() method is called when the applet is first loaded. It is used to perform initialization tasks, such as setting up the applet's graphical user interface (GUI), loading resources, and initializing variables.

2. start()

The start() method is called after the init() method and whenever the applet is restarted or resumed after being stopped or paused. It is responsible for starting the applet's operation, such as starting animations or running calculations.

3. stop()

The stop() method is called when the applet is stopped or paused, such as when the user navigates away from the web page or switches to a different tab. It is used to suspend resource-intensive operations and free up system resources.

4. destroy()

The destroy() method is called when the applet is no longer needed, such as when the web page is closed or refreshed. It is responsible for cleaning up resources, releasing memory, and performing any necessary shutdown tasks.

Creating a Java Applet

To create a Java applet, you need to follow these steps:

1. Create a Java Class


import java.applet.Applet;
import java.awt.Graphics;

public class MyJavaApplet extends Applet {
  public void paint(Graphics g) {
    // Applet drawing code here
  }
}

2. Compile the Java Class

Compile the Java class using the Java compiler, which will generate the bytecode file with a .class extension.

3. Embed the Applet in HTML

Create an HTML file and use the <applet> tag to embed the Java applet within the web page. You can specify the applet's width, height, and other parameters within the tag.


<html>
  <head>
    <title>My Java Applet</title>
  </head>
  <body>
    <applet code="MyJavaApplet.class" width="400" height="300">
      Your browser does not support Java applets.
    </applet>
  </body>
</html>

4. Run the Applet

Open the HTML file in a Java-enabled web browser, and the applet will be displayed within the web page. Note that some modern web browsers may not support Java applets due to security concerns or lack of plugin support.

Java applets were once a popular way of adding dynamic content to websites, but they have fallen out of favor in recent years due to security vulnerabilities and the rise of alternative web technologies. However, learning about Java applets can still provide insights into the history and evolution of web development.

Now that you have an understanding of Java applets, you can explore more advanced topics such as interactivity, event handling, and multimedia integration to create richer applet experiences. Happy coding!

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