iterator 遍历与for循环与foreach的优劣对比

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我是靠谱客的博主热心大船，最近开发中收集的这篇文章主要介绍iterator 遍历与for循环与foreach的优劣对比，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

最近看到项目上有这样的语句

Iterator it = list.iterator();
    while (it.hasNext()) {
        objects = (Object[]) iter.next();
    }

瞬间感觉比起自己的for循环语句高端大气了不少，但此刻又有疑问，到底这两种那种比较好

先拿出for循环来对比

for(int i=0;i <list.size();i++){
objects = (Object[])list.get(i);
}

经过查询，查到了很多，现在来分享一下

一方面从简洁程度和可复用的角度，迭代器的方法必然比较轻松，比如当前list的组织结构变化，不能用get（）函数获取，则需要重新更改for循环代码，而迭代器不用，故这是开发爱好者比较喜欢的一种代码方式

至于效率方面，找到了一位大神的测试分析http://bbs.csdn.net/topics/250025827

现在拷贝一些关键数据

import java.util.Iterator;
import java.util.List;
import java.util.ArrayList;
import java.util.LinkedList;

/**
 * IteratorTest
 * @author SageZk
 */
public class IteratorTest {

	public static long testForloops(List<String> list) {
		long start = 0L, end = 0L;
		@SuppressWarnings("unused")
		String le = null;
		start = System.nanoTime();
		for (int i = list.size() - 1; i >= 0; --i) {
			le = list.get(i);
		}
		end = System.nanoTime();
		return end - start;
	}

	public static long testIterator(List<String> list) {
		long start = 0L, end = 0L;
		@SuppressWarnings("unused")
		String le = null;
		start = System.nanoTime();
		Iterator<String> it = list.iterator();
		while (it.hasNext()) {
			le = it.next();
		}
		end = System.nanoTime();
		return end - start;
	}

	public static void main(String[] args) {
		//测试列表长度
		final int LEN = 10000;

		//初始化测试用数据
		List<String> arraylist = new ArrayList<String>();
		List<String> linkedlist = new LinkedList<String>();
		for (int i = 0; i < LEN; ++i) {
			String s = Integer.toString(i, 2);
			arraylist.add(s);
			linkedlist.add(s);
		}

		//打印测试结果
		final String FORMAT = "%1$-16s%2$-16s%3$16dn";
		System.out.println("ListttTypettTime(nanoseconds)");
		System.out.println("-------------------------------------------------");
		System.out.printf(FORMAT, "ArrayList", "for", testForloops(arraylist));
		System.out.printf(FORMAT, "ArrayList", "Iterator", testIterator(arraylist));
		System.out.printf(FORMAT, "LinkedList", "for", testForloops(linkedlist));
		System.out.printf(FORMAT, "LinkedList", "Iterator", testIterator(linkedlist));
	}

}

以下是 3 组测试结果：

[code=BatchFile]List Type Time(nanoseconds)
-------------------------------------------------
ArrayList       for                      1189258
ArrayList       Iterator                 2365594
LinkedList      for                    152396254
LinkedList      Iterator                 2340801

List Type Time(nanoseconds)
-------------------------------------------------
ArrayList       for                      1235701
ArrayList       Iterator                 4249982
LinkedList      for                    149825606
LinkedList      Iterator                 2525531

List Type Time(nanoseconds)
-------------------------------------------------
ArrayList       for                      1198267
ArrayList       Iterator                 2584617
LinkedList      for                    150382451
LinkedList      Iterator                 2347994
[/code]