code: @Override
  	public void visitClassContext(ClassContext classContext) {
  		try {
  			stack = new OpcodeStack();
  			localMethodCalls = new HashMap<>();
  			fieldMethodCalls = new HashMap<>();
  			staticMethodCalls = new HashMap<>();
  			branchTargets = new BitSet();
  			super.visitClassContext(classContext);
  		} finally {
  			stack = null;
  			localMethodCalls = null;
  			fieldMethodCalls = null;
  			staticMethodCalls = null;
  			branchTargets = null;
  		}
  	}
docs: implements the visitor to create and clear the stack, method call maps, and
  branch targets
  
  @param classContext the context object of the currently visited class