Matchbox is a TV set top box UI that iRex uses to implement several bits of their UI. In particular the toolbar with the trash can, keyboard (as well as the pop up keyboard itself).
http://matchbox-project.org
Unfortunately iRex ships the Java with the addressable display area set to 768x935. I've already found that if I modify my iLiad startup sequence to start X and then the Java I can cut the boot time in half. But I can't implement a full replacement UI in Java since I can't draw into the bottom part of the display: yet!!!
There is also a version of the JVM available from Tao-Group that has direct framebuffer drivers. If this was installed one wouldn't even need to start the X server... reducing boot time even more. Maybe iRex will wake up a realize the possibilities.
I put the compiled Java code in jar's and then use a fuse ssh mount to copy it over but there are many available options for transferring files to the iLiad.
http://fuse.sourceforge.net/
http://fuse.sourceforge.net/sshfs.html
You get PBP-1.0 with the JVM they also have Xlet support buried in there as well, and that appears to have a more complete AWT implementation available to it.