The code behind it is quite complicated, and involves the AlphaComposite class and a bunch of mathematics. Most of the shadow code is located in the Light class, and you can check out how it works if you want, since the source is freely available.

Very true Cheribasa, I originally made it as a quick game to test out an old highscore idea that another member had, and was very surprised at how quickly it took off.

You should add some more objects or features, that way it's not just a direct copy of mine. I do like the code though! The original was written a long time ago when I was not nearly as experienced as I am now, and it's nice to see the idea still getting some attention. Great job!