I guess I will be the first one to say it...
EDIT: Arrgh you beat me!!!
NO!!!
There is no Java for the classic Amiga line.
There is no AmigaOS hosted Java YET for the next gen Amiga line either.
There is a clean java virtual machine in the works called JAmiga but I would think that is only reasonable for the next gen machines and that is nowhere near complete either.
Also, AmigaDE, which is sure to be ported to the A1 at some point in the future and maybe even PegasOS will feature Java compilation, but that is probably limited to J2ME or personal Java dialects which are prominent on PDAs and perhaps your mobile phone. The difference in dialect may cause you to have trouble with the port of Java for the desktop without AmigaDE in that case.
You can buy the AmigaDE SDK right now if you like, but its take up appears to have been disasterously low, but I think everyone is hanging back to see if AmigaInc enhance it and whether it becomes integrated in the AmigaOS. IMHO it a cool tech and it would be a shame if it was not hosted as standard on AmigaOS.
Maybe if you run Linux on your classic hardware you might have a chance of writing java but even then I doubt it.
There is a vbcj(?) compiler which could theoretically be ported to give you Java on a classic machine but that is far far away from being finished and lacks almost all the graphics libraries you'd probably want to use.
Sorry, dude, I want to write in Java too, but we're SOL!!!
The Amiga platform, as it stands right now, is probably the worst platform to even consider writing stuff in Java for, even as a crossport to another platform.
What's the Java on Aminet all about? Is that Jamiga?
Dudes, feel free to correct me if I'm wrong, which I could very well be.