java bytecode editor?
bytecode, java
Solution
Nothing decent with a UI, but you can use the Eclipse Bytecode Outline plugin to turn any Java class into ASM code, edit it, and produce the changed class. It's probably the most painless way at the moment.
http://asm.ow2.org/eclipse/index.html
Problem
What's a good free bytecode editor? I want an editor, something with a GUI... I tried jbe-0.1b with no luck (can't save the bytecode changes).