ExecutorTest.java

import java.util.Date;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import algorithm.Solver;

/**
 * @author nazarov
 */
public class ExecutorTest {
	public static void main(String[] args) throws ExecutionException,	InterruptedException {
		final ForkJoinPool pool = new ForkJoinPool(4);
		final Solver solver = new Solver(0, 200000000);
		
		double start = new Date().getTime()/1000.0;
		
		pool.invoke(solver);
		
		double end = new Date().getTime()/1000.0;
		
		System.out.println(solver.result);
		System.out.print("Done in: ");
		System.out.print(end-start);
		System.out.println(" s");
	}
}

sample output

1.927317886402193
Done in: 27.70899987220764 s

Solver.java

package algorithm;

import java.util.concurrent.RecursiveAction;

/**
 * @author nazarov
 */
public class Solver extends RecursiveAction {
	private int _from;
	private int _to;
	public double result;

	public Solver(int from, int to) {
		_from = from;
		_to   = to;
	}

	@Override
	protected void compute() {
		if (_to - _from < 1000000) {
			result = 0;
			for(int i = _from; i < _to; i++)
				result += Math.sin(i);
		} else {
			int mid = _from + (_to-_from) / 2;
			Solver s1 = new Solver(_from, mid);
			s1.fork();
			Solver s2 = new Solver(mid, _to);
			s2.compute();
			s1.join();
			result = s1.result + s2.result;
		}
	}
}