The technology is called decompilation. There are many decompilers available, like: cavaj jad
BTW, this is not the correct forum for your post.(CarefullyChooseOneForum) It probably belongs to Java Intermediate. [ August 18, 2008: Message edited by: Nitesh Kant ]
Note that the more popular free decompilers (like jad and Jode) are stuck in the Java 1.4 world, and will ignore Java 5 features. So their value isn't what it used to be. [ August 19, 2008: Message edited by: Ulf Dittmer ]