Applications to recompile jar contents

[lagiwed]

Helo guys can U help me about recompiling or compresing jar contents. I used to decompile or extract jar contents 2 edit something(like translating or editing the class file).. My problem is when I recompile the jar contents theres a 'BIG' change in the jar size.. Even if I decompile the jar contents 'without editing' and when I recompile it the size still change.. Or is there a way to insert a single file inside the jar without decompiling it. Bcuz I see some edited java game(the jar contents are edited) but the size is still close to the original size..
So guys can U say what application to use to recompile or compres the jar contents with out a BIG change of its size.
Thank you..