Reverse engineer Java application

I want to rebuild MotiveWave, a charting tool, from its jars. This application has a feature (probably in one of the class files but I don't know which) that i want to build upon. I mean I want to inherit that class and use it in another custom class. The jars are without the source code. I have tried jd to view the source of jars and was able to view some of the code. What I want is to build and run it in debug and then access that specific feature using the UI to see which class gets triggered. So following would be needed 1. Do a feasibility review (Can it be done?) 2. Figure out the class that has the code (probably by building in eclipse and debugging?). Probably also re-write this class (make it public such that it can be inherited/used further). 3. Write a new class inheriting that class (see point 2). I will tell you what is needed in this new class when you contact me. I have the application (with jars) with me.