rainbow comes with tetris, minesweeper and and an arc editor that use the swing library from java so there is lots of sample code to work from. If you've used swing before, you should find it pretty easy from rainbow, and I've tried to design the arc interface so it looks as arc-ish and un-java-ish as possible.

But please bear in mind rntz's observation about the long-term goals of the 100-year language; I'm pretty sure java integration is way off the bottom of the list :)