Here are a few applets I wrote for amusement while teaching myself Java.
A friend was having a hard time visualizing how two colliding waves could cancel each other, so I wrote this applet to illustrate the effect. It could also serve as a small (four term) introduction to Fourier analysis.
Rollovers can be used to produce interesting effects such as buttons that light up when touched with the cursor. I've produced a few simple examples. Feel free to borrow the code to make some for yourself.
Good places to begin finding information about Java are the Sun Java site & the developer.com site, formerly known as Gamelan and now absorbed by Earthweb. Once you know the basic language, the book Java Examples in a Nutshell by David Flanagan, O'Reilly & Assoc, 1997, is highly recommended.