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; } }