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> jiSuanJi = new HashMap>();
		Map ruanJian = new HashMap();
		Map wangZhan = new HashMap();
		
		/*
		 * 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) new HashMap().put("01", "haha"));
		//jiSuanJi.put("yingyong", (Map) 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 keySet = jiSuanJi.keySet();
		for(Iterator it = keySet.iterator();it.hasNext();) {
			String key = it.next();
			System.out.println(key);
			Map map = jiSuanJi.get(key);
			Set> entrySet = map.entrySet();
			for(Iterator> it2 = entrySet.iterator();it2.hasNext();) {
				Map.Entry 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> jiSuanJi = new HashMap>();
		List ruanJian = new ArrayList();
		List wangZhan = new ArrayList();
		
		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 keySet = jiSuanJi.keySet();
		for(Iterator it = keySet.iterator();it.hasNext();){
			String key = it.next();
			System.out.println(key);
			List list = jiSuanJi.get(key);
			for(Iterator 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;
	}
	
	
}