/**
 * 继承RecursiveTask 则每个子任务带返回值
 * 继承RecursiveAction 则每个子任务不带返回值
 */
public class FockJoin1 extends RecursiveTask<Integer>{


    public static void main(String[] args) throws ExecutionException, InterruptedException {
        long l = System.currentTimeMillis();
        ForkJoinPool pool = new ForkJoinPool();                         //类似线程池，也实现了AbstractExecutorService
        FockJoin1 task = new FockJoin1(1,1000000000);         //新建任务
        Future<Integer> result = pool.submit(task);                     //将任务提交
        System.out.println("result is" + result.get());                 //获取结果
        System.err.println(System.currentTimeMillis() - l);
    }

    private final Integer index = 5000; //分割任务的基数
    private final Integer left;
    private final Integer right;

    public FockJoin1(Integer left, Integer right) {
        this.left = left;
        this.right = right;
    }
    
    @Override
    protected Integer compute() {
        int sum = 0;
        if(right - left < index) {                      //如果任务 小于基数，则直接执行；类似递归的出口
            for (int i = left; i <= right; i++) {
                sum += i;
            }
        }else {                                         //任务 大于基数，则分割，类似与二分法，也可以更多
            int middle = (right + left) >> 1;
            FockJoin1 myf1 = new FockJoin1(left, middle);           //二分法左边
            FockJoin1 myf2= new FockJoin1(middle+1, right);    //二分法右边
            myf1.fork();                                            //继续执行，类似递归
            myf2.fork();                                            //继续执行，类似递归
            Integer integer1 = myf1.join();                         //等待
            Integer integer2 = myf2.join();
            sum = integer1 + integer2;                              //结果合并
        }
        return sum;
    }
}