Compute

分隔符

// 将 _ 作为数字的分隔符  以下为 10亿
for (Long i = 1L; i <= 10_0000_0000; i++) {
    sum += i;
}

ForkJoin

并行执行任务！提高效率。大数据量！ 大数据：Map Reduce （把大任务拆分为小任务）

ForkJoin 特点：工作窃取

这个里面维护的都是双端队列

package com.zy.forkjoin;
import java.util.concurrent.RecursiveTask;
/**
 * 求和计算的任务！
 * 
 * //  使用 forkjoin
 * // 1、forkjoinPool 通过它来执行
 * // 2、计算任务  forkjoinPool.execute(ForkJoinTask task)
 * // 3、计算类要继承 ForkJoinTask
 * @author zhangyu
 */
public class ForkJoinDemo extends RecursiveTask<Long> {
    // 初始值  1
    private Long start;
    // 结束值   1990900000
    private Long end;  
    // 临界值
    private Long temp = 10000L;
    public ForkJoinDemo(Long start, Long end) {
        this.start = start;
        this.end = end;
    }
    // 计算方法
    @Override
    protected Long compute() {
        if ((end - start) < temp) {
            Long sum = 0L;
            for (Long i = start; i <= end; i++) {
                sum += i;
            }
            return sum;
        } else {
             // 中间值
            long middle = (start + end) / 2;
            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();
        }
    }
}

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.stream.DoubleStream;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
/**
 * 效率高几十倍！
 * @author zhangyu
 */
public class Test {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        // test1(); // 12224
        // test2(); // 10038
        // test3(); // 153
    }
    // 普通程序员
    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));
    }
    // 使用ForkJoin
    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));
    }
    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="+"时间："+(end-start));
    }
}