code: private void buildMethodFieldModifiers(ClassContext classContext) {
          FieldModifier fm = new FieldModifier();
          fm.visitClassContext(classContext);
          methodFieldModifiers = fm.getMethodFieldModifiers();
      }
docs: builds up the method to field map of what method write to which fields this is one recursively so that if method A calls method B, and method B writes to
  field C, then A modifies F.
  
  @param classContext
  the context object of the currently parsed class