After seven months' work, I now have Kaffe running on the 4000 under OS3.9. It uses ixemul, so it suffers from the speed penalty of a Linux emulation.
So far I have ported the interpreter and the two current versions of the JIT. The JITs run about 10x faster than the interpreter, as you would expect.
I haven't looked at AWT - it relies on X, so it won't work on an Amiga. It will have to be re-written.
As someone said, Kaffe is compatible with Java 1.4 (I think) in most respects. There is a long list of incompatibilities, just waiting for people to fix. Most are silly things like "Kaffe gives the wrong error message here".
When I get my A1, I'm going to have to start again with the PPC version. The JIT engine for the PPC platform is just now being written, and I hope to be involved with its development Real Soon Now.
tony