java Map集合嵌套，value为Map和value为List



java Map集合嵌套，value为Map和value为List.

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
 
 
public class MapDemo {
 
public static void main(String[] args) {
System.out.println("Map集合的值为Map");
oneToMap();
 
System.out.println("Map集合的值为List，特别常用！必须会！");
oneToList();
}
 
/*
* 这种是把班级和学生作为映射
* 而且又把学号和姓名做了映射
*/
public static void oneToMap() {
Map<STRING,MAP<STRING,STRING>> jiSuanJi = new HashMap<STRING,MAP<STRING,STRING>>();
Map<STRING,STRING> ruanJian = new HashMap<STRING,STRING>();
Map<STRING,STRING> wangZhan = new HashMap<STRING,STRING>();
 
/*
* 千万不要每次都new一个进去，这样就不是原来的集合了
* 结果yingyong这个key对应的value集合是null
* 遍历Map的时候还会出现空指针错误
*/
//jiSuanJi.put("yingyong", (Map<STRING, String>) new HashMap().put("01", "haha"));
//jiSuanJi.put("yingyong", (Map<STRING, String>) new HashMap().put("02", "xixi"));
 
/*
* 要使用下面这种方式，先把集合定义好，
* 把映射关系设置好，再去给集合添加元素
*/
jiSuanJi.put("ruanJian", ruanJian);
jiSuanJi.put("wangZhan", wangZhan);
 
ruanJian.put("01", "zhangsan");
ruanJian.put("02", "lisi");
 
wangZhan.put("01", "zhaoliu");
wangZhan.put("02", "zhouqi");
 
Set<STRING> keySet = jiSuanJi.keySet();
for(Iterator<STRING> it = keySet.iterator();it.hasNext();) {
String key = it.next();
System.out.println(key);
Map<STRING,STRING> map = jiSuanJi.get(key);
Set<MAP.ENTRY<STRING, String>> entrySet = map.entrySet();
for(Iterator<MAP.ENTRY<STRING, String>> it2 = entrySet.iterator();it2.hasNext();) {
Map.Entry<STRING, String> me = it2.next();
System.out.println(me.getKey() + ".." + me.getValue());
}
}
}
 
/*
* 这种把班级和学生做了映射
* 学生类中封装了学号和姓名
*/
public static void oneToList() {
Map<STRING,LIST<PERSONDEMO>> jiSuanJi = new HashMap<STRING,LIST<PERSONDEMO>>();
List<PERSONDEMO> ruanJian = new ArrayList<PERSONDEMO>();
List<PERSONDEMO> wangZhan = new ArrayList<PERSONDEMO>();
 
jiSuanJi.put("ruanJian", ruanJian);
jiSuanJi.put("wangZhan", wangZhan);
 
ruanJian.add(new PersonDemo("01","zhangsan"));
ruanJian.add(new PersonDemo("02","lisi"));
wangZhan.add(new PersonDemo("01","wangwu"));
wangZhan.add(new PersonDemo("02","zhaoliu"));
 
Set<STRING> keySet = jiSuanJi.keySet();
for(Iterator<STRING> it = keySet.iterator();it.hasNext();){
String key = it.next();
System.out.println(key);
List<PERSONDEMO> list = jiSuanJi.get(key);
for(Iterator<PERSONDEMO> it2 = list.iterator();it2.hasNext();) {
PersonDemo pd = it2.next();
System.out.println(pd);
}
}
}
 
}
 
class PersonDemo {
 
private String id;
private String name;
 
public PersonDemo(String id, String name) {
super();
this.id = id;
this.name = name;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return this.id + "..." + this.name;
}
 
 
}