a fork join demo

ForkJoinDemo.java

/**
 * 
 */
package demo;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Random;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveTask;
import java.util.stream.Collectors;

/**
 * a fork join demo
 * 
 * @author adyliu (imxylz@gmail.com)
 * @since 2014年12月16日
 */
public class ForkJoinDemo {
    final static int SEED = 100;
    final static Random r = new Random();

    static class Poa {
        final long count = r.nextInt(SEED);
    }

    static class Doa {
        List<Poa> poas = Arrays.stream(new int[r.nextInt(SEED)]).mapToObj(t -> new Poa()).collect(Collectors.toList());

        long sum() {
            return poas.stream().mapToLong(poa -> poa.count).sum();
        }
    }

    static class Trip {
        List<Doa> doas = Arrays.stream(new int[r.nextInt(SEED)]).mapToObj(t -> new Doa()).collect(Collectors.toList());

        long sum() {
            return doas.stream().mapToLong(doa -> doa.sum()).sum();
        }
    }

    static class SumTask extends RecursiveTask<Long> {
        Trip trip;
        List<Trip> trips = new ArrayList<>();
        List<SumTask> tasks = new ArrayList<>();

        public SumTask(List<Trip> trips) {
            this.trips = trips;
        }

        public SumTask(Trip trip) {
            this.trip = trip;
        }

        @Override
        protected Long compute() {
            long sum = 0;
            for (Trip t : trips) {
                SumTask task = new SumTask(t);
                tasks.add(task);
                task.fork();
            }
            if (trip != null) {
                sum += trip.sum();
            }
            for (SumTask task : tasks) {
                sum += task.join();
            }
            return sum;
        }
    }

    public static void main(String[] args) throws Exception {
        List<Trip> trips = Arrays.stream(new int[r.nextInt(SEED)]).mapToObj(t -> new Trip()).collect(Collectors.toList());
        //
        final SumTask sumTask = new SumTask(trips);
        final ForkJoinPool forkJoinPool = new ForkJoinPool();
        long sum = forkJoinPool.invoke(sumTask);
        //
        System.out.println(sum);
        forkJoinPool.shutdown();
    }

}