Develop a small animation using applet, graphics and multithreading.

Description

To develop a small animation using an Applet, you’d use the java.applet, java.awt.Graphics, and java.lang.Thread classes. This combination allows you to create a moving visual element within a web browser, powered by a separate thread to ensure smooth animation without freezing the user interface. This is a classic example of how multithreading is used to handle time-consuming tasks in the background.

1. The Applet and Graphics

The Applet class provides the framework for a Java program that can run within a web browser. The core of the animation logic resides within its methods.

• init(): This method is called when the applet is first loaded. You would typically initialize variables and create objects here, such as the thread for the animation.
• paint(Graphics g): This is the method responsible for drawing the visual elements. The Graphics object, passed as an argument, acts as a canvas. You use its methods, like drawRect(), fillOval(), or drawString(), to render shapes and text on the applet.
• repaint(): This method tells the Applet to update its display, which in turn calls the paint() method. To create animation, you need to call repaint() repeatedly.

To create the illusion of movement, you’d update the position of an object (e.g., a circle’s x and y coordinates) and then call repaint(). The paint() method would then redraw the object at its new position.

2. Multithreading for Smooth Animation

Using a separate thread is critical for a good animation. If you were to run the animation logic directly in the Applet’s main thread, the user interface would become unresponsive. A dedicated thread allows the animation to run independently in the background.

• Runnable Interface: You’d create a class that implements the Runnable interface. This class holds the main animation loop.
• The run() Method: This method contains the logic for the animation. In a simple loop, you’d:
  1. Update the coordinates of the object.
  2. Call repaint().
  3. Pause the thread for a short period using Thread.sleep() to control the animation speed (e.g., a 20ms pause for 50 frames per second).

By separating the animation logic into its own thread, the Applet remains responsive to user input, and the animation is smooth. This is a fundamental concept in software development, where a producer-consumer model is often used to ensure that a task (like animating) doesn’t block the main application thread.