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; 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])));
   }
 }