private static class SumTask extends RecursiveTask{

  //设定计算长度的阈值为总长度的十分之一也就是一千万
  private final static int THRESHOLD = MakeArray.ARRAY_LENGTH/10;
  private int[] src; //表示我们要实际统计的数组
  private int fromIndex;//开始统计的下标
  private int toIndex;//统计到哪里结束的下标

  public SumTask(int[] src, int fromIndex, int toIndex) {
    this.src = src;
    this.fromIndex = fromIndex;
    this.toIndex = toIndex;
  }

  @Override
  protected Integer compute() {
    //计算长度如果小于设定长度就不需要分解任务
    if(toIndex-fromIndex < THRESHOLD) {
      int count = 0;
      for(int i=fromIndex;i<=toIndex;i++) {
        count = count + src[i];
      }
      return count;
    }else {
      int mid = (fromIndex+toIndex)/2;
      SumTask left = new SumTask(src,fromIndex,mid);
      SumTask right = new SumTask(src,mid+1,toIndex);
      //将任务进行拆分
      invokeAll(left,right);
      //连接返回结果
      return left.join()+right.join();
    }
  }
}

public static void main(String[] args) {
  ForkJoinPool pool = new ForkJoinPool();
  int[] src = MakeArray.makeArray();
  SumTask innerFind = new SumTask(src,0,src.length-1);
  long start = System.currentTimeMillis();
  pool.invoke(innerFind);//同步调用
}