I am pretty lucky in my day to day work that I have access to nearly all of the source code for the software I work with. (Even the close hold Java security code which is very useful when working on the HTTP Analyzer). Sometimes you run across a snippet of code that for whatever reason you don't have the source code to hand. JDeveloper will generate you a stub; but that is not so useful when you want to know what is going on.
There is a kind-of hidden feature in JDeveloper called the bytecode debugger that you can enable by selecting "Show Bytecode":
This will show you the method in question in terms of bytecodes, and you can use the new extra pink toolbar icons to step at the bytecode level or just use the normal ones to step in at the java method level.
Very useful when you are stuck and for very good legal reasons cannot make use of java dissembly tools.