I'm trying to install a stable version of freebsd on my pc, which will be used to run 1 java application only, it no need to support the latest hardware, but need to be very stable. Any recommendation?
Any version of FreeBSD is going to be relatively stable (especially compared the the other options on the market).
If you look at FreeBSD's website, you'll note that 4.10 is their "production release" which would be considered "very stable." If you're a tad more daring you might be interested in trying version 5.2.1 named the "new technology release."
The truth is, either will probably be fine for you use, but if stability is really a main concern, go with 4.10.