I've looked in the code, and saw your PI variable where you enter a enormous number of decimals. That is useless, since it can't be stored in a double. If you really feel like needing much decimals, take a look at the BigDecimal class in Java.

(First time on Greenfoot in months and months and months!) I haven't looked over the source code, but from what SPower said I'm assuming you're storing a value for pi. You can actually just use Math.PI :) http://docs.oracle.com/javase/6/docs/api/java/lang/Math.html#PI

To make it even faster, what you could do is what all games of today do: draw on a smaller image and scale that up. Maybe the result is very bad, but you can always try and not post it if it's bad :)