java 集合（Map）

import java.util.*;

public class ex12 {
    public static void main(String[] args) {
        Map<String, String> map = new HashMap<String, String>();//为什么改成int会报错
        map.put("Tom", "1");
        map.put("Jack", "2");
        map.put("Yoo", "3");
        map.put("Peter", "4");
        map.put("LiLi", "5");
        System.out.println(map);

        System.out.println();
        Map<String, String> map2 = new HashMap<String,String>();
        map2.put("AAAAA","1");
        map2.put("PPPPP","6");
        map.putAll(map2);//把map2 的所有添加到map 集合中
        System.out.println(map);//注意该行输出的结果

        System.out.println();
        System.out.println("remove(Object key)=====" + map2.remove("AAAAA"));//注意返回值
        System.out.println("remove(Object key)=====" + map2.remove("BBBBB"));
        System.out.println();
        // System.out.println("clear()=======" + map2.clear());//报错
        map2.clear();
        System.out.println(map2);//清空所有

        System.out.println();
        System.out.println(map.get("PPPPP"));
        System.out.println(map.size());

        System.out.println();
        System.out.println(map.isEmpty());
        
    }
}