You should do some research on the LWJGL (light weight java game library). It gives Java the power of OpenGL, which is a hardware accelerated graphics library. It can be a bit complicated, but if you are up to the task it can be very worth it! Just think, Minecraft was built using Java and the LWJGL :D
Thanks, I've actually been digging into the Minecraft source code recently, so I end up choking on nostalgia.
JMonkey is also a good way to go. In my opinion, it is an excellent next IDE after Greenfoot. I also believe that it is compatible with android (several people have used it to create paid apps). It is also free. I myself am actually working on an Eden spinoff of it (Eden is a spinoff of Minecraft that works on android).
