Module java.base

Class RecursiveTask<V>

Type Parameters:
V - the type of the result of the task
All Implemented Interfaces:
Serializable, Future<V>

public abstract class RecursiveTask<V> extends ForkJoinTask<V>
A recursive result-bearing ForkJoinTask.

For example, here is a task-based program for computing Factorials:

 import java.util.concurrent.RecursiveTask;
 import java.math.BigInteger;
 public class Factorial {
   static class FactorialTask extends RecursiveTask<BigInteger> {
     private final int from, to;
     FactorialTask(int from, int to) { this.from = from; = to; }
     protected BigInteger compute() {
       int range = to - from;
       if (range == 0) {                       // base case
         return BigInteger.valueOf(from);
       } else if (range == 1) {                // too small to parallelize
         return BigInteger.valueOf(from).multiply(BigInteger.valueOf(to));
       } else {                                // split in half
         int mid = from + range / 2;
         FactorialTask leftTask = new FactorialTask(from, mid);
         leftTask.fork();         // perform about half the work locally
         return new FactorialTask(mid + 1, to).compute()
   static BigInteger factorial(int n) { // uses ForkJoinPool.commonPool()
     return (n <= 1) ? BigInteger.ONE : new FactorialTask(1, n).invoke();
   public static void main(String[] args) {
See Also:
  • Constructor Details

    • RecursiveTask

      public RecursiveTask()
      Constructor for subclasses to call.
  • Method Details

    • compute

      protected abstract V compute()
      The main computation performed by this task.
      the result of the computation
    • getRawResult

      public final V getRawResult()
      Description copied from class: ForkJoinTask
      Returns the result that would be returned by ForkJoinTask.join(), even if this task completed abnormally, or null if this task is not known to have been completed. This method is designed to aid debugging, as well as to support extensions. Its use in any other context is discouraged.
      Specified by:
      getRawResult in class ForkJoinTask<V>
      the result, or null if not completed
    • setRawResult

      protected final void setRawResult(V value)
      Description copied from class: ForkJoinTask
      Forces the given value to be returned as a result. This method is designed to support extensions, and should not in general be called otherwise.
      Specified by:
      setRawResult in class ForkJoinTask<V>
      value - the value
    • exec

      protected final boolean exec()
      Implements execution conventions for RecursiveTask.
      Specified by:
      exec in class ForkJoinTask<V>
      true if this task is known to have completed normally