JODE is a java package containing a decompiler and an optimizer for
java. This package is freely available under the GNU GPL. The bytecode
package and the core decompiler is now under GNU Lesser General Public
License, so you can integrate it in your project.

Can be used from command line or through the Swing-based GUI.

The decompiler reads in class files and produces something similar to
the original java file. Jode has support for all constructs of JDK-1.3
including inner and anonymous classes.

The optimizer transforms class files in various ways with can be
controlled by a script file. It supports the following operations:

 
	. Renaming class, method, field and local names to shorter,
	  obfuscated, or unique names or according to a given
	  translation table
	. Removing debugging information
	. Removing dead code (classes, fields, methods) and constant
	  fields
	. Optimizing local variable allocation

WWW: http://jode.sourceforge.net/