摘自：http://blog.csdn.net/jkh753/article/details/11651599

package threadpool;

import java.sql.Time;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class ListTest {
	public static void main(String[] args) {
		long begin,end;
		List<String> list = new ArrayList<String>();
		for(int i = 0 ;i<=10000000 ;i++){
			list.add("abcd"+i);
		}
		System.out.println("first way:");
		begin = System.currentTimeMillis();
		for(String str: list){
			
		}
		end = System.currentTimeMillis();
		System.out.println("takes " + (end-begin) +"ms");
		
		System.out.println("second way:");
		begin = System.currentTimeMillis();
		for(int i=0;i<= list.size();i++){
			
		}
		end = System.currentTimeMillis();
		System.out.println("takes " + (end-begin) +"ms");
		
		System.out.println("third way:");
		Iterator<String> iterator = list.iterator();
		begin = System.currentTimeMillis();
		while(iterator.hasNext()){
			iterator.next();
		}
		end = System.currentTimeMillis();
		System.out.println("takes " + (end-begin) +"ms");
	}
}

本机测试结果如下：first way:

takes 79ms

second way:

takes 0ms

third way:

takes 16ms