jdk8学习笔记七

package com.atguigu.java8;

import java.util.concurrent.RecursiveTask;

public class ForkJoinCalculate extends RecursiveTask<Long>{

    /**
     * 
     */
    private static final long serialVersionUID = 13475679780L;

    private long start;
    private long end;

    private static final long THRESHOLD = 10000L; //临界值

    public ForkJoinCalculate(long start, long end) {
        this.start = start;
        this.end = end;
    }

    @Override
    protected Long compute() {
        long length = end - start;

        if(length <= THRESHOLD){
            long sum = 0;

            for (long i = start; i <= end; i++) {
                sum += i;
            }

            return sum;
        }else{
            long middle = (start + end) / 2;

            ForkJoinCalculate left = new ForkJoinCalculate(start, middle);
            left.fork(); //拆分，并将该子任务压入线程队列

            ForkJoinCalculate right = new ForkJoinCalculate(middle+1, end);
            right.fork();

            return left.join() + right.join();
        }

    }

}

package com.atguigu.java8;

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

import org.junit.Test;

public class TestForkJoin {

    @Test
    public void test1(){
        long start = System.currentTimeMillis();

        ForkJoinPool pool = new ForkJoinPool();
        ForkJoinTask task = new ForkJoinCalculate(0L, 10000000000L);

        long sum = pool.invoke(task);
        System.out.println(sum);

        long end = System.currentTimeMillis();

        System.out.println("耗费的时间为: " + (end - start)); //112-1953-1988-2654-2647-20663-113808
    }

    @Test
    public void test2(){
        long start = System.currentTimeMillis();

        long sum = 0L;

        for (long i = 0L; i <= 10000000000L; i++) {
            sum += i;
        }

        System.out.println(sum);

        long end = System.currentTimeMillis();

        System.out.println("耗费的时间为: " + (end - start)); //34-3174-3132-4227-4223-31583
    }

    @Test
    public void test3(){
        long start = System.currentTimeMillis();

        Long sum = LongStream.rangeClosed(0L, 10000000000L)
                             .parallel()
                             .sum();

        System.out.println(sum);

        long end = System.currentTimeMillis();

        System.out.println("耗费的时间为: " + (end - start)); //2061-2053-2086-18926
    }

}