/* * Written by Doug Lea with assistance from members of JCP JSR-166 * Expert Group and released to the public domain, as explained at * http://creativecommons.org/publicdomain/zero/1.0/ */ package java.util.concurrent; /** * A recursive result-bearing {@link ForkJoinTask}. * *
For example, here is a task-based program for computing Factorials: * *
{@code * import java.util.concurrent.RecursiveTask; * import java.math.BigInteger; * public class Factorial { * static class FactorialTask extends RecursiveTask* * @since 1.7 * @author Doug Lea */ public abstract class RecursiveTask{ * private final int from, to; * FactorialTask(int from, int to) { this.from = from; this.to = 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() * .multiply(leftTask.join()); * } * } * } * static BigInteger factorial(int n) { // uses ForkJoinPool.commonPool() * return (n <= 1) ? BigInteger.ONE : new FactorialTask(1, n).invoke(); * } * public static void main(String[] args) { * System.out.println(factorial(Integer.parseInt(args[0]))); * } * }}