I'm working on a refactoring tool that uses only the frontend of extendj, and thus I found two unwanted dependencies toward the backend. For reproductibility just run the ant frontend task in java 8.
The problem comes from the equation boolean BodyDecl.isField() located in java4/backend/GenerateClassfile.jrag
Once this equation has been imported to be able to compile the generated java classes, the FieldDecl.hasInit() method located in java4/backend/CreateBCode.jrag is also required.
If these two methods/equations are moved in some frontend files, the frontend is correctly decoupled from the backend.