map的循环遍历方式

package com.sec.map;

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

public class TestMap {

    public static void main(String[] args) {


          Map<String, String> map = new HashMap<String, String>();

          map.put("1", "value1");

          map.put("2", "value2");

          map.put("3", "value3");


          //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));

          }

          System.out.println("www.javaweb.top");

          //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());

          }

          System.out.println("www.javaweb.top");

          //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());

          }

          System.out.println("www.javaweb.top");

          //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);

          }

          System.out.println("www.javaweb.top");
         }

}