import java.util.concurrent.*;

/**
 * Created by Mr.Jo on 2018/9/10.
 */
public class Main{

    static class CountTask extends RecursiveTask<Integer> {

        private static final int f = 2;
        private int start;
        private int end;

        public CountTask(int start, int end) {
            this.start = start;
            this.end = end;
        }
        @Override
        protected Integer compute() {
            int sum = 0;

            boolean canCompute = (end - start) <= f;
            if (canCompute) {
                for (int i = start; i <= end; i++) {
                    sum += i;
                }
            } else {
                int mid = (start + end) / 2;
                CountTask leftTask = new CountTask(start, mid);
                CountTask rightTask = new CountTask(mid+1, end);
                leftTask.fork();
                rightTask.fork();
                int leftResult = leftTask.join();
                int rightResult = rightTask.join();
                sum = leftResult + rightResult;
            }
            return sum;
        }
    }

    public static void main(String[] args) throws InterruptedException, ExecutionException {
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        CountTask task = new CountTask(1, 100);

        Future<Integer> result = forkJoinPool.submit(task);

        System.out.println(result.get());
    }
}