map 的四种遍历方式

import java.util.HashMap;import java.util.Iterator;import java.util.Map;/** * Created by Administrator on 17/6/6. */public class Test {    public static void main(String[] args){        Map<String, String> map = new HashMap<String, String>();        map.put("1", "value1");        map.put("3", "value3");        map.put("2", "value2");//第一种：普遍使用，二次取值        System.out.println("通过Map.keySet遍历key和value：");        for (String key : map.keySet()) {            System.out.println("key= "+ key + " and value= " + map.get(key));        }        //第二种        System.out.println("通过Map.entrySet使用iterator遍历key和value：");        Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();        while (it.hasNext()) {            Map.Entry<String, String> entry = it.next();            System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());        }        //第三种：推荐，尤其是容量大时        System.out.println("通过Map.entrySet遍历key和value");        for (Map.Entry<String, String> entry : map.entrySet()) {            System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());        }        //第四种        System.out.println("通过Map.values()遍历所有的value，但不能遍历key");        for (String v : map.values()) {            System.out.println("value= " + v);        }    }}