Writing a Java Applet

Create an applet that will run in a Java compatible web browser by subclassing the java.applet.Applet superclass. Using what you know about threads, launch an animation thread that will display itself in the browser without blocking user input from the keyboard and mouse. Have the animation pause and unpause with a mouse click or accept some other kinds of input. In terms of design, you may want to create a general Animation class as either an abstract class and have the Animator applet instantiate a subcalss of that. This way, the various implementations of Animation can be swapped in without altering the Animator applet.

For example: 

abstract class Animation
{
	...
	public abstract void drawNextFrame(Graphics g);
	...
}

public class Animator extends Applet implements Runnable
{
	private Animation animation_;
	private Image image_buffer_;		
	private boolean thread_alive_;
	...

	public void run()
	{
		...
		Graphics g = image_buffer_.getGraphics();
		while (thread_alive_)
		{
			animation_.drawNextFrame(g);
			Thread.sleep(100);
		}
		...
	}
}

To really improve the visual quality of the animation, use a technique called Double Buffering. Instead of drawing the animation frame directly to the screen, draw to an offscreen image and then display the entire image at once. When making multiple graphics method calls on the display, a viewer may notice the drawing process. If the drawing process is hidden from the user, the transition between frames appears much smoother.

View the applet.

Script to run the Applet demo

References

Flanagan, David; Java in a Nutshell, Sections 4 and 8 on Applets and Advanced Graphics
The Java tutorial is a useful online resource, especially the chapters on writing applets and performing animation.
Look at the Javasoft Java API Documentation on the java.applet package.