A vaguely Space Invaders game meant for teaching people to learn to program games. It is well documented. The only code you need is SpaceBalls.java and GameApplet.java.
Would you like to see the source code or download the program? You can get the files you need here. If you can't see the whole applet, you can press F11 for fullscreen mode or change your screen's resolution.
UW Madison >> CS department >> Tim's website >> SpaceBalls