A few months ago i started using KJAR to compress jar files. It worked well, eliminating 10% space of a 110KB jar file. But it turned out to have a trojan horse virus in it which my anti-virus software eventually dealt with. So beware!
If anyone has an uninfected version i would like to hear from you.
Here is the site (which is otherwise excellent) where i got the infected KJar http://supremej2me.bambalam.se