RecursiveTask (Java Platform SE 8 )
Keywords: java.util.concurrent.RecursiveTask class
Date: 2020-03-26

compact1, compact2, compact3
java.util.concurrent

## Class RecursiveTask<V>

- java.lang.Object
- - java.util.concurrent.ForkJoinTask<V>
  - - java.util.concurrent.RecursiveTask<V>

- All Implemented Interfaces:
    Serializable, Future<V>

      public abstract class RecursiveTask<V>
      extends ForkJoinTask<V>

  A recursive result-bearing `ForkJoinTask`.

  For a classic example, here is a task computing Fibonacci numbers:

       class Fibonacci extends RecursiveTask<Integer> {
         final int n;
         Fibonacci(int n) { this.n = n; }
         Integer compute() {
           if (n <= 1)
             return n;
           Fibonacci f1 = new Fibonacci(n - 1);
           f1.fork();
           Fibonacci f2 = new Fibonacci(n - 2);
           return f2.compute() + f1.join();
         }
       }

  However, besides being a dumb way to compute Fibonacci functions (there is a simple fast linear algorithm that you'd use in practice), this is likely to perform poorly because the smallest subtasks are too small to be worthwhile splitting up. Instead, as is the case for nearly all fork/join applications, you'd pick some minimum granularity size (for example 10 here) for which you always sequentially solve rather than subdividing.
  Since:
    1.7
  See Also:
    Serialized Form

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `RecursiveTask()`

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected abstract V` | `compute()` The main computation performed by this task.
    `protected boolean` | `exec()` Implements execution conventions for RecursiveTask.
    `V` | `getRawResult()` 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.
    `protected void` | `setRawResult(V value)` Forces the given value to be returned as a result.

    - ### Methods inherited from class java.util.concurrent.ForkJoinTask

      `adapt, adapt, adapt, cancel, compareAndSetForkJoinTaskTag, complete, completeExceptionally, fork, get, get, getException, getForkJoinTaskTag, getPool, getQueuedTaskCount, getSurplusQueuedTaskCount, helpQuiesce, inForkJoinPool, invoke, invokeAll, invokeAll, invokeAll, isCancelled, isCompletedAbnormally, isCompletedNormally, isDone, join, peekNextLocalTask, pollNextLocalTask, pollTask, quietlyComplete, quietlyInvoke, quietlyJoin, reinitialize, setForkJoinTaskTag, tryUnfork`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### RecursiveTask

          public RecursiveTask()

  - ### Method Detail

    - #### compute

          protected abstract V compute()

      The main computation performed by this task.
      Returns:
        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>`
      Returns:
        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>`
      Parameters:
        `value` - the value

    - #### exec

          protected final boolean exec()

      Implements execution conventions for RecursiveTask.
      Specified by:
        `exec` in class `ForkJoinTask<V>`
      Returns:
        `true` if this task is known to have completed normally

Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2020, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.