I'm pretty sure (but am hedging here :) that you would get any errors in the verification phase of loading a class. What you saw may have been due to bugs in th

I'm pretty sure (but am hedging here :) that you would get any errors in the verification phase of loading a class. What you saw may have been due to bugs in that library you were using. Anyway, this was before ASM and other bytecode engineering libraries. Today I would not directly hack the class def myself.