A full working JVM with graphics has never been implemented on the Amiga for a number of reasons:
a) Its far too slow on a 68K based system
b) The graphics are probably the hardest to implement on Amigas gfx system (none of the current Amiga JVMs support gfx)
c) Any current JVM projects have been abandoned.
Best thing is to use PC Windows, Linux or Mac for JVM. AmigaOS 4 will eventually support JVM.
Also, remember that Java IS NOT the same as Java script. Amiga supports Javascript very well. IBrowse 2.3 supports latest JS.