从c/c++语言转向java开发，学习java语言list遍历的三种方法，顺便测试各种遍历方法的性能，测试方法为在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，测试代码例如以下：
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!!!!!!!!"); } } |
测试结果例如以下：
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!!!!!!!!
测试的结论非常奇怪，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？
