java中遍历map的四种方法

package com.yang.mapdemo;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

public class MapDemo {

    public static void main(String[] args) {
        Map<String, String> map = new HashMap<String, String>();
        map.put("1", "first");
        map.put("2", "second");
        map.put("3", "third");

        //1.通过Map.keySet遍历key和value
        for(String key : map.keySet()){
            System.out.println("key="+key+", value="+map.get(key));
        }

        //2.通过Map.entrySet使用iterator遍历key和value
        System.out.println("-------------------");
        Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
        while(it.hasNext()){
            Entry<String, String> entry = it.next();
            System.out.println("key="+entry.getKey()+", value="+entry.getValue());
        }

        //3.通过Map.entrySet遍历key和value(推荐,尤其是容量大时)
        System.out.println("-------------------");
        for(Map.Entry<String,String> entrySet : map.entrySet()){
            System.out.println("key="+entrySet.getKey()+", value="+entrySet.getValue());
        }

        //4.通过Map.values()遍历所有的value，但不能遍历key
        System.out.println("-------------------");
        for(String a : map.values()){
            System.out.println("value="+a);
        }






    }

}