Understanding Java Byte Code

Question

Often I am stuck with a java class file with no source and I am trying to understand the problem I have at hand.

Note a decompiler is useful but not sufficient in all si

Answer 1

If you have a class and no source code, but you have a bug, you can do one of two basic things:

1. Decompile, fix the bug and recreate the jar file. I have done this before, but sysadmins are leery about putting that into production.

2. Write unit tests for the class, determine what causes the bug, report the bug with the unit tests and wait for it to be fixed.

   (2) is generally the one that sysadmins, in my experience, prefer.

   If you go with (2) then, in the meantime, since you know what causes the bug, you can either not allow that input to go to the class, to prevent a problem, or be prepared to properly handle it when the error happens.

   You can also use AspectJ to inject code into the problem class and change the behavior of the method without actually recompiling. I think this may be the preferable option, as you can change it for all code that may call the function, without worrying about teaching everyone about the problem.

   If you learn to read the bytecode instructions, what will you do to solve the problem?