code: @Override
      public void visitClassContext(ClassContext classContext) {
          try {
              stack = new OpcodeStack();
              ifBlocks = new IfBlocks();
              gotoBranchPCs = new BitSet();
              casePositions = new BitSet();
              super.visitClassContext(classContext);
          } finally {
              stack = null;
              ifBlocks = null;
              catchPCs = null;
              gotoBranchPCs = null;
              casePositions = null;
          }
      }
docs: implements the visitor to reset the opcode stack, and initialize if tracking collections
  
  @param classContext
  the currently parsed java class