ForkJoin 计算0~10亿内和的方法

ForkJoin

在大数据量的情况下，并行执行任务，提高效率

把大任务拆分成小任务

package com.zhong.forkjoin;

import java.util.concurrent.RecursiveTask;

/** ForkJoin之三种计算0~10亿内和值方法
 * ForkJoin 并行执行任务，提高效率，大数据量
 */
public class ForkJoinDemo extends RecursiveTask<Long> {

    private Long start;
    private Long end;

    //临界值
    private Long temp = 10000L;

    public ForkJoinDemo(Long start, Long end){
        this.start = start;
        this.end = end;
    }

    //计算的方法
    @Override
    protected Long compute() {
        if ( (end-start)<temp ){
            Long sum = 0L;
            for (Long i = start; i <= end ; i++) {
                sum += i;
            }
            return sum;
        } else {
            //forkjoin 递归
            long middle = (start + end) / 2; //中间值
            ForkJoinDemo task1 = new ForkJoinDemo(start, middle);
            task1.fork();//拆分任务，把任务压入线程队列
            ForkJoinDemo task2 = new ForkJoinDemo(middle+1, end);
            task2.fork();//拆分任务，把任务压入线程队列
            return task1.join() + task2.join();
        }
    }
}

测试类

package com.zhong.forkjoin;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.stream.LongStream;

public class Test {

    public static void main(String[] args) throws ExecutionException, InterruptedException {

        test1(); //7688
        test2(); //8186
        test3(); //139
    }

    /*
        操作比较大的数的时候，注意溢出问题
        JDK7新特性，数字之间可以用下划线分割
        int money = 10_0000_0000;
    */

    //普通人, 用this。来调
    public static void test1(){
        Long sum = 0L;
        long start = System.currentTimeMillis();
        for (Long i = 1L; i <= 10_0000_0000 ; i++) {
            sum += i;
        }
        long end = System.currentTimeMillis();
        System.out.println("sum= "+ sum +" 时间：" + (end-start));
    }

    //会用ForkJoin的
    public static void test2() throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> task = new ForkJoinDemo(0L,10_0000_0000L);
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);//提交任务
        Long sum = submit.get();
        long end = System.currentTimeMillis();
        System.out.println("sum= "+ sum +" 时间：" + (end-start));
    }

    //Stream 并行流
    public static void test3(){
        long start = System.currentTimeMillis();
        //Stream 并行流
        long sum = LongStream.rangeClosed(0L,10_0000_0000L).parallel().reduce(0, Long::sum);
        long end = System.currentTimeMillis();
        System.out.println("sum= "+ sum +" 时间：" + (end-start));
    }
}