ForkJoinPool.commonPool().invokeAll(...)

package ch.claude_martin;

import java.util.List;
import java.util.concurrent.*;
import java.util.stream.*;

public final class SomeClass implements Callable<Integer> {

  private final int value;

  public SomeClass(int i) {
    this.value = i;
  }

  @Override
  public Integer call() throws Exception {
    System.out.println("started: " + value);
    Thread.sleep((long) (1000 * Math.random()));
    System.out.println("finished: " + value);
    return value;
  }

  public static void main(String[] args) throws InterruptedException {
    // List of 10 instances of SomeClass:
    List<SomeClass> tasks = IntStream.range(0, 10).mapToObj(i -> new SomeClass(i))
        .collect(Collectors.toList());

    // This would work, but is sequential instead of parallel:
    // tasks.stream().map(ForkJoinPool.commonPool()::submit)
    // This would work, but it messes up the order:
    // tasks.parallelStream().map(ForkJoinPool.commonPool()::submit)

    // Process the list and print all results in correct order:
    ForkJoinPool.commonPool().invokeAll(tasks).stream()
      .map(t -> {
        try {
          return t.get();
        } catch (InterruptedException | ExecutionException e) {
          // Java isn't exactly elegant when it comes to streams and exceptions
          throw new RuntimeException(e);
        }
      }).forEach(System.out::println);

    // Not necessary, but to really make sure the tasks are all processed:
    ForkJoinPool.commonPool().awaitTermination(100, TimeUnit.SECONDS);
    System.out.flush();
  }
}