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RecursiveTask

public abstract class RecursiveTask
extends ForkJoinTask<V>

java.lang.Object
   ↳ java.util.concurrent.ForkJoinTask<V>
     ↳ java.util.concurrent.RecursiveTask<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; }
   protected 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.

Summary

Public constructors

RecursiveTask()

Public methods

final V getRawResult()

Returns the result that would be returned by join(), even if this task completed abnormally, or null if this task is not known to have been completed.

Protected methods

abstract V compute()

The main computation performed by this task.

final boolean exec()

Implements execution conventions for RecursiveTask.

final void setRawResult(V value)

Forces the given value to be returned as a result.

Inherited methods

Public constructors

RecursiveTask

added in API level 21
public RecursiveTask ()

Public methods

getRawResult

added in API level 21
public final V getRawResult ()

Returns the result that would be returned by 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.

Returns
V the result, or null if not completed

Protected methods

compute

added in API level 21
protected abstract V compute ()

The main computation performed by this task.

Returns
V the result of the computation

exec

added in API level 21
protected final boolean exec ()

Implements execution conventions for RecursiveTask.

Returns
boolean true if this task is known to have completed normally

setRawResult

added in API level 21
protected final void setRawResult (V value)

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.

Parameters
value V: the value