Is it possible to inherit a final class modifying bytecode somehow?

Question

Is it possible to inherit a final class using bytecode manipulations?

Answer 1

Yes and no.

You can use bytecode manipulation to change a final class to non-final on the fly. This doesn't even break binary compatibility, so there is no risk of class loader / verifier errors.

However, you have to apply the bytecode modifications to the final class itself. You can't do bytecode manipulation on a child class to make it inherit from a final parent class. Or more precisely, if you do that the modified child class will be rejected by the verifier when loaded together with the final parent class.

Answer 2

This describes the class file format. At the offset 10+cpsize there are 2 bytes defining the access flags of this class. One of these flags is called ACC_FINAL (0x0010). I suppose you can mask that bit out and make that class non-final.