list遍历实现方式跟效率的差别 -

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list遍历实现方式跟效率的差别

博客分类：

java

Java

1:14109
2:14000
3:15141
4:14297

package com.zbalpha.test;

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

public class ListTest {
    public static void main(String args[]){
        List<Long> lists = new ArrayList<Long>();

        for(Long i=0l;i<1000000l;i++){
            lists.add(i);
        }

        Long oneOk = oneMethod(lists);
        Long twoOk = twoMethod(lists);
        Long threeOk = threeMethod(lists);
        Long fourOk = fourMethod(lists);

        System.out.println("One:" + oneOk);
        System.out.println("Two:" + twoOk);
        System.out.println("Three:" + threeOk);
        System.out.println("four:" + fourOk);

    }

    public static Long oneMethod(List<Long> lists){
        Long timeStart = System.currentTimeMillis();
        for(int i=0;i<lists.size();i++)    {
            System.out.println(lists.get(i));
        }
        Long timeStop = System.currentTimeMillis();

        return timeStop -timeStart ;
    }

    public static Long twoMethod(List<Long> lists){
        Long timeStart = System.currentTimeMillis();
        for(Long string : lists)    {
            System.out.println(string);
        }
        Long timeStop = System.currentTimeMillis();

        return timeStop -timeStart ;
    }

    public static Long threeMethod(List<Long> lists){

        Long timeStart = System.currentTimeMillis();
        Iterator<Long> it = lists.iterator();
        while (it.hasNext())
        {
                System.out.println(it.next());
        }
        Long timeStop = System.currentTimeMillis();

        return timeStop -timeStart ;
    }



    public static Long fourMethod(List<Long> lists){

        Long timeStart = System.currentTimeMillis();
        for(Iterator<Long> i = lists.iterator(); i.hasNext();)    {
            System.out.println(i.next());
        }
        Long timeStop = System.currentTimeMillis();

        return timeStop -timeStart ;
    }
}

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