Landon Fuller has made significant progress on porting the FreeBSD JDK to Mac OS X. Not everything works yet, but Swing does, which is further than I think anyone else has gotten. According to Fuller, "There are, of course, still some significant bugs, and I'm continuing to work on hotspot Darwin i386 ABI stack alignment issues. I think things are probably a week or so away from a day-to-day usable amd64/Leopard release, and farther for i386/Leopard & Tiger."