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Java™ Platform
Standard Ed. 7

DRAFT ea-b118

java.util.concurrent
Class RecursiveTask<V>

java.lang.Object
  extended by java.util.concurrent.ForkJoinTask<V>
      extended by 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
Constructor and Description
RecursiveTask()
           
 
Method Summary
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, complete, completeExceptionally, fork, get, get, getException, getPool, getQueuedTaskCount, getSurplusQueuedTaskCount, helpQuiesce, inForkJoinPool, invoke, invokeAll, invokeAll, invokeAll, isCancelled, isCompletedAbnormally, isCompletedNormally, isDone, join, peekNextLocalTask, pollNextLocalTask, pollTask, quietlyInvoke, quietlyJoin, reinitialize, 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.


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 completed normally

Java™ Platform
Standard Ed. 7

DRAFT ea-b118

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.

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DRAFT ea-b118

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