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);        }    }}