Sun's Java compiler and libraries aren't in the Debian archives because they aren't free
, even though they can be downloaded at no cost from Sun's Java website
. Sun does provide this software for linux, but if you want to use free software, look for information about "gcj". It should be in the Debian archive. I don't think its libraries provide as much GUI support as Sun's, but I imagine its developers are working on that (quite a monumental task, really).