java Map集合嵌套，value为Map和value为List

忘是亡心i 2022-03-06 09:24 620阅读 0赞

# java Map集合嵌套，value为Map和value为List #

2013年12月13日 23:13:34 [wuer0520][] 阅读数：12476

1.  `import java.util.ArrayList;`
2.  `import java.util.HashMap;`
3.  `import java.util.Iterator;`
4.  `import java.util.List;`
5.  `import java.util.Map;`
6.  `import java.util.Set;`
7.   
8.   
9.  `public class MapDemo {`
10.  
11. `public static void main(String[] args) {`
12. `System.out.println("Map集合的值为Map");`
13. `oneToMap();`
14.  
15. `System.out.println("Map集合的值为List，特别常用！必须会！");`
16. `oneToList();`
17. `}`
18.  
19. `/*`
20. `* 这种是把班级和学生作为映射`
21. `* 而且又把学号和姓名做了映射`
22. `*/`
23. `public static void oneToMap() {`
24. `Map<String,Map<String,String>> jiSuanJi = new HashMap<String,Map<String,String>>();`
25. `Map<String,String> ruanJian = new HashMap<String,String>();`
26. `Map<String,String> wangZhan = new HashMap<String,String>();`
27.  
28. `/*`
29. `* 千万不要每次都new一个进去，这样就不是原来的集合了`
30. `* 结果yingyong这个key对应的value集合是null`
31. `* 遍历Map的时候还会出现空指针错误`
32. `*/`
33. `//jiSuanJi.put("yingyong", (Map<String, String>) new HashMap().put("01", "haha"));`
34. `//jiSuanJi.put("yingyong", (Map<String, String>) new HashMap().put("02", "xixi"));`
35.  
36. `/*`
37. `* 要使用下面这种方式，先把集合定义好，`
38. `* 把映射关系设置好，再去给集合添加元素`
39. `*/`
40. `jiSuanJi.put("ruanJian", ruanJian);`
41. `jiSuanJi.put("wangZhan", wangZhan);`
42.  
43. `ruanJian.put("01", "zhangsan");`
44. `ruanJian.put("02", "lisi");`
45.  
46. `wangZhan.put("01", "zhaoliu");`
47. `wangZhan.put("02", "zhouqi");`
48.  
49. `Set<String> keySet = jiSuanJi.keySet();`
50. `for(Iterator<String> it = keySet.iterator();it.hasNext();) {`
51. `String key = it.next();`
52. `System.out.println(key);`
53. `Map<String,String> map = jiSuanJi.get(key);`
54. `Set<Map.Entry<String, String>> entrySet = map.entrySet();`
55. `for(Iterator<Map.Entry<String, String>> it2 = entrySet.iterator();it2.hasNext();) {`
56. `Map.Entry<String, String> me = it2.next();`
57. `System.out.println(me.getKey() + ".." + me.getValue());`
58. `}`
59. `}`
60. `}`
61.  
62. `/*`
63. `* 这种把班级和学生做了映射`
64. `* 学生类中封装了学号和姓名`
65. `*/`
66. `public static void oneToList() {`
67. `Map<String,List<PersonDemo>> jiSuanJi = new HashMap<String,List<PersonDemo>>();`
68. `List<PersonDemo> ruanJian = new ArrayList<PersonDemo>();`
69. `List<PersonDemo> wangZhan = new ArrayList<PersonDemo>();`
70.  
71. `jiSuanJi.put("ruanJian", ruanJian);`
72. `jiSuanJi.put("wangZhan", wangZhan);`
73.  
74. `ruanJian.add(new PersonDemo("01","zhangsan"));`
75. `ruanJian.add(new PersonDemo("02","lisi"));`
76. `wangZhan.add(new PersonDemo("01","wangwu"));`
77. `wangZhan.add(new PersonDemo("02","zhaoliu"));`
78.  
79. `Set<String> keySet = jiSuanJi.keySet();`
80. `for(Iterator<String> it = keySet.iterator();it.hasNext();){`
81. `String key = it.next();`
82. `System.out.println(key);`
83. `List<PersonDemo> list = jiSuanJi.get(key);`
84. `for(Iterator<PersonDemo> it2 = list.iterator();it2.hasNext();) {`
85. `PersonDemo pd = it2.next();`
86. `System.out.println(pd);`
87. `}`
88. `}`
89. `}`
90.  
91. `}`
92.  
93. `class PersonDemo {`
94.  
95. `private String id;`
96. `private String name;`
97.  
98. `public PersonDemo(String id, String name) {`
99. `super();`
100. `this.id = id;`
101. `this.name = name;`
102. `}`
103. `public String getId() {`
104. `return id;`
105. `}`
106. `public void setId(String id) {`
107. `this.id = id;`
108. `}`
109. `public String getName() {`
110. `return name;`
111. `}`
112. `public void setName(String name) {`
113. `this.name = name;`
114. `}`
115. `@Override`
116. `public String toString() {`
117. `return this.id + "..." + this.name;`
118. `}`
119.  
120.  
121. `}`

[wuer0520]: https://me.csdn.net/wuer0520