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<String> list = new ArrayList<String>();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<String> 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？