TextPad is a really straightforward way to do it. But if you want something that offers a little more functionality look at NetBeans IDE or Eclipse. They will tell you errors as you are coding rather than after you compile.
You need a reverse or de-compiler that meets or exceeds the original version. You will probably get replacement names for almost everything not a native or well known API class, including language primitives, and then only the class name will be right, not the instance or object reference name. For example, it should tell you which objects / references are 'String', 'Integer' or for object 'System'.
Some use pre- or post-compilers to ensure all original name traces are replaced, so reverse compiling does not easily reveal functionality and method.