HashMap遍历

package com.huawei.scp.api.query;import java.util.HashMap;import java.util.Map;import java.util.Map.Entry;// HashMap的遍历有两种常用的方法，使用keyset及entryset来进行遍历，但两者的遍历速度是有差别的。public class TestHashMap{    public static void main(String[] args)    {        Map<String, Integer> map1 = new HashMap<String, Integer>();        map1.put("a", 0);        map1.put("b", 1);        map1.put("c", 2);        // keyset遍历        System.out.println("keyset遍历-----------");        for (String key : map1.keySet())        {            Integer value = map1.get(key);            System.out.println("key:" + key + " value:" + value);        }        // entryset遍历        System.out.println("\nentryset遍历-----------");        for (Entry<String, Integer> entry : map1.entrySet())        {            String key = entry.getKey();            Integer value = entry.getValue();            System.out.println("key:" + key + " value:" + value);        }        // 两者性能测试        System.out.println("\n两者性能区别-----------");        Map<String, Integer> map2 = new HashMap<String, Integer>();        for (int i = 0; i < 99999; i++)        {            map2.put(String.valueOf(i), i);        }        // keyset遍历时间        long time1Start = System.currentTimeMillis();        for (String key : map2.keySet())        {            Integer value = map2.get(key);            // System.out.println("key:" + key + " value:" + value);        }        long time1End = System.currentTimeMillis();        System.out.println("keyset遍历需要时间:" + (time1End - time1Start));        // entryset遍历时间        long time2Start = System.currentTimeMillis();        for (Entry<String, Integer> entry : map2.entrySet())        {            String key = entry.getKey();            Integer value = entry.getValue();            // System.out.println("key:" + key + " value:" + value);        }        long time2End = System.currentTimeMillis();        System.out.println("entryset遍历需要时间:" + (time2End - time2Start));    }}

输出结果:

keyset遍历-----------key:b value:1key:c value:2key:a value:0entryset遍历-----------key:b value:1key:c value:2key:a value:0两者性能区别-----------keyset遍历需要时间:16entryset遍历需要时间:0