JAVAmap容器基本使用

import java.io.PrintWriter;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;
import java.util.Iterator;

public class Main {
    static PrintWriter cout = new PrintWriter(System.out, true);
    static Scanner cin = new Scanner(System.in);
    
    public static void main (String[] args){
        HashMap<String, String> map = new HashMap<String, String>();
        map.put("China", "中国");
        map.put("China", "zhongguo"); //键已存在，将"中国"覆盖
        map.put("Japen", "日本");
        map.put("American", "美国");
        //输出map容器的大小
        cout.println(map.size());
        //以数组形式,打印map容器
        cout.println(map.entrySet());
        //以数组形式打印键
        cout.println(map.keySet());
        //以数组形式打印值
        cout.println(map.values());
        //判断是否存在某个键
        if(map.containsKey("China"))
        {
            cout.println("find success");
        }
        else
        {
            cout.println("losing finding");
        }
        //判断是否存在某个值
        if(map.containsValue("中国"))
        {
            cout.println("find success");
        }
        else
        {
            cout.println("losing finding");
        }
        //按键寻值
        cout.println(map.get("China"));
        //不存在则返回null
        cout.println(map.get("china"));
        
        //map容器遍历
        //方法一:
        for(Map.Entry<String, String> entry : map.entrySet())
        {
            cout.println("Key="+entry.getKey()+", Value="+entry.getValue());
        }
        
        //方法二:增加了按键寻值,效率低
        for(String s : map.keySet())
        {
            cout.println("Key="+s+", Value="+map.get(s));
        }
        //方法三：最快
        for(Iterator<Map.Entry<String, String>> it=map.entrySet().iterator();it.hasNext();)
        {
            Map.Entry<String, String> entry = it.next();
            System.out.println("key:"+entry.getKey()+", value:"+entry.getValue());
        }
        
        //将容器清空
        map.clear();
        //判断容器是否为空
        cout.println(map.isEmpty());
    }
}