leetcode-go/basis/concurrent/TestForkjoin.java

import java.util.concurrent.*;

public class TestForkjoin {
    public static void main(String[] args) throws Exception {
        MyRecursiveTask fj = new MyRecursiveTask(1, 100000);
        ForkJoinPool pool = new ForkJoinPool();
        Future future = pool.submit(fj);
        System.out.println(future.get());
    }
}

class MyRecursiveTask extends RecursiveTask<Integer> {
    private final int threshold = 5;
    private int beg;
    private int end;

    MyRecursiveTask(int beg, int end) {
        this.beg = beg;
        this.end = end;
    }

    @Override
    protected Integer compute() {
        if (end - beg <= threshold) {
            int count = 0;
            for (int i = beg; i <= end; i++)
                count++;
            return count;
        }
        int mid = beg + (end - beg) / 2;
        MyRecursiveTask left = new MyRecursiveTask(beg, mid);
        MyRecursiveTask right = new MyRecursiveTask(mid + 1, end);
        left.fork();
        right.fork();
        return left.join() + right.join();
    }
}