从c/c++语言转向java开发，学习java语言list遍历的三种方法，顺便測试各种遍历方法的性能，測试方法为在ArrayList中插入1千万条记录，然后遍历ArrayList，发现了一个奇怪的现象，測试代码例如以下：

package com.hisense.tiger.list;import java.util.ArrayList;import java.util.Iterator;import java.util.List;public class ListTest {	public static void main(String[] args)	{		List
     
       list = new ArrayList
      
       ();		long t1,t2;		for(int j = 0; j < 10000000; j++)		{			list.add("aaaaaa" + j);		}		System.out.println("List first visit method:");		t1=System.currentTimeMillis();		for(String tmp:list)		{			//System.out.println(tmp);		}		t2=System.currentTimeMillis();		System.out.println("Run Time:" + (t2 -t1) + "(ms)");		System.out.println("List second visit method:");				t1=System.currentTimeMillis();		for(int i = 0; i < list.size(); i++)		{			list.get(i);			//System.out.println(list.get(i));		}		t2=System.currentTimeMillis();		System.out.println("Run Time:" + (t2 -t1) + "(ms)");				System.out.println("List Third visit method:");		Iterator
       
         iter = list.iterator();				t1=System.currentTimeMillis();		while(iter.hasNext())		{			iter.next();			//System.out.println(iter.next());		}		t2=System.currentTimeMillis();		System.out.println("Run Time:" + (t2 -t1) + "(ms)");						System.out.println("Finished!!!!!!!!");					}}
       
      
     

    測试结果例如以下：

List first visit method:

Run Time:170(ms)

List second visit method:

Run Time:10(ms)

List Third visit method:

Run Time:34(ms)

Finished!!!!!!!!

    測试的结论非常奇怪，第一种方法是java语言支持的新语法，代码最简洁，可是在三种方法中，性能确是最差的，取size进行遍历性能是最高的，求牛人解释？