for那种方式效率最高

最新推荐文章于 2024-02-26 14:17:08 发布

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本文通过实验比较了Java中不同集合操作方式的时间消耗，包括基本的for循环、foreach、while循环和迭代器方法，旨在为开发者提供高效集合操作的指导。

package com.data.struct;

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

public class Test2 {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<Integer>();

        int runTime = 1000;//执行次数
        for (int i = 0; i < 1000 * 1000; i++) {
            list.add(i);
        }
        int size = list.size();
        long currTime = System.currentTimeMillis();//开始分析前的系统时间
        //基本的for            
        for(int j = 0; j < runTime; j++) {
            for (int i = 0; i < size; i++) {
                list.get(i);
            }
        }
        long time1 = System.currentTimeMillis();

        //foreach
        for(int j = 0; j < runTime; j++) {
            for (Integer integer : list) {
            }
        }
        long time2 = System.currentTimeMillis();

        for(int j = 0; j < runTime; j++) {
            //while
            int i = 0 ;
            while(i < size){
                list.get(i++);
            }
        }
        long time3 = System.currentTimeMillis();

        for(int j = 0; j < runTime; j++) {//普通for循环
            for (int i = 0; i < list.size(); i++) {
                list.get(i);
            }
        }
        long time4 = System.currentTimeMillis();

        for(int j = 0; j < runTime; j++) {//迭代
            Iterator<Integer> iter = list.iterator();
            while(iter.hasNext()) {
                iter.next();
            }
        }
        long time5 = System.currentTimeMillis();

        long time = time1 - currTime ;
        System.out.print("use for:" + time);
        time = time2 - time1;
        System.out.print("\tuse foreach:" + time);
        time = time3 - time2;
        System.out.print("\tuse while:" + time);
        time = time4 - time3;
        System.out.print("\tuse for2:" + time);
        time = time5 - time4;
        System.out.print("\tuse iterator:" + time);
        System.out.println();
    }
}

use for:6035	use foreach:13345	use while:5930	use for2:9853	use iterator:11767