Iterator迭代器和foreach增强for循环的效率比较

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我是靠谱客的博主复杂诺言，最近开发中收集的这篇文章主要介绍Iterator迭代器和foreach增强for循环的效率比较，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

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package cn.jiguang.base64;

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

import org.junit.Test;

public class CollectionTest {

   public void JDK8DataTimeClockTest() {

   }

   @Test
   public void foreachQuery() {
       int count = 0;
       Map<String, String> map = new HashMap<String, String>();
       for (int i = 0; i < 100000; i++) {
           map.put("key=" + i, "value=" + i);
       }

       long startTimeFor = System.currentTimeMillis();
       for (Entry<String, String> entry : map.entrySet()) {
           System.out.println(entry.getKey());
           System.out.println(entry.getValue());
           count++;
       }
       System.out.println("查询记录数=" + count);
       System.out.println("增强for查询耗时：" + (startTimeFor - System.currentTimeMillis()));
   }

   @Test
   public void iteratorQuery() {
       int count = 0;
       Map<String, String> map = new HashMap<String, String>();
       for (int i = 0; i < 1000000; i++) {
           map.put("key=" + i, "value=" + i);
       }

       Iterator<Entry<String, String>> iterator = map.entrySet().iterator();
       long startTimeIterator = System.currentTimeMillis();
       while (iterator.hasNext()) {
           String key = iterator.next().getKey();
           String value = iterator.next().getValue();
           System.out.println(key);
           System.out.println(value);
           count++;
       }
       System.out.println("查询记录数=" + count);
       System.out.println("迭代器Iterator查询耗时：" + (startTimeIterator - System.currentTimeMillis()));
   }
}