HashMap中的几种遍历方式对比

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

/**
 * @Author：KoVaVo
 * @Version：1.0.0
 * @Description：
 */
public class HashMapTest {
    public static void main(String[] args) {
        //hashMap的几种便利方式
        HashMap<Integer, String> hashMap = new HashMap<Integer, String>();
        hashMap.put(1,"1");
        hashMap.put(2,"2");
        hashMap.put(3,"3");
        System.out.println("=====keyset=====");
        long l = System.currentTimeMillis();
        for (int key : hashMap.keySet()) {
            System.out.println(key+"..."+hashMap.get(key));
        }
        System.out.println(l-System.currentTimeMillis());
        System.out.println("=====iterator=====");
        l=System.currentTimeMillis();
        Iterator<Map.Entry<Integer, String>> iterator = hashMap.entrySet().iterator();
        while (iterator.hasNext()){
            Map.Entry<Integer,String> next = iterator.next();
            System.out.println(next.getValue()+"...iterator");
        }
        System.out.println(l-System.currentTimeMillis());
        System.out.println("=====entryset=====");
        l=System.currentTimeMillis();
        for (Map.Entry<Integer, String> entry : hashMap.entrySet()) {
            System.out.println(entry.getValue());
        }
        System.out.println(l-System.currentTimeMillis());
    }
}