code: @Override
      public void visitClassContext(ClassContext classContext) {
          currentClass = classContext.getJavaClass();
  
          if (currentClass.getMajor() >= Const.MAJOR_1_8) {
              try {
                  stack = new OpcodeStack();
                  activeStackOps = new ArrayDeque<>();
                  super.visitClassContext(classContext);
              } finally {
                  activeStackOps = null;
                  stack = null;
              }
          }
          currentClass = null;
      }
docs: implements the visitor to filter out pre-1.8 classes, for 1.8+ classes, it creates the opcode stack and active stack ops
  
  @param classContext
  the context object of the currently parsed class