基本的概念

Class class=null 【只是在棧內存中有了指向，堆內存並沒有分配內存】

Class class=new Class()【棧內存中有了指向（引用），堆內存也分配了內存】

map的嵌套實現樹

Map<object,object> map = new HashMap<>();

Map<Object, Object> map = new HashMap<>();
        Map<Object, Object> temp =map;
        temp.put(1,1);
        Map
 
<Object, Object> map1 = new HashMap<>();
        map1.put(1,"child");
        temp.put("child",map1);
        
        temp = map1;
        
        Map<Object, Object> map2 = new HashMap<>();
        map2.put(2,"child2");
        temp.put("child2",map2);
        System.out.println(map);
 

61 dfa 實現敏感詞過濾