Jikes RVM is a bleeding-edge research project. You will find that some of the code does not live up to product quality standards. Don't hesitate to help rectify this by contributing clean-ups, bug fixes, and missing documentation to the project. We are in the process of consolidating and simplifying the codebase at the moment.
From release 2.9.0, it is possible to edit JikesRVM in an IDE such as eclipse