KJar is a simple tool that recompresses jar files using the superior zip compressor KZip
which is featured on Supreme J2ME. It helped a lot reducing 5ud0ku's jar size below the 63K boundary which enables it to run on some devices which have a 63K limit. I never thought of the option of recompression. So have a look at Supreme J2ME for the utility as well as for other tools and tips on J2ME optimization.