Jad, a Java decompiler. This program is able to reads one or more
Java class files and convert them back into Java source files
which can be recompiled. 

Jad is a C++ program and it generally works several times faster
than decompilers written in Java.

No source code is available for this program. Jad is free for
non-commercial use, but not for commercial use.

WWW: http://kpdus.tripod.com/jad.html