import java.util.Random;

import java.util.concurrent.*;

/**

* Count the number of occurences of a number in an array using Fork/Join framework.

*

* @author L.Gobinath

*/

public class SearchArray {

public static void main(String[] args) {

int[] array = {5, 6, 3, 2, 8, 1, 5, 5, 3, 9, 7, 5, 2, 4};

// Search for 5

Counter counter = new Counter(5, array, 0, array.length - 1);

// Create a pool of threads

ForkJoinPool pool = new ForkJoinPool();

// Start execution and wait for result

int count = pool.invoke(counter);

System.out.println("Count: " + count); // Count: 4

}

}

class Counter extends RecursiveTask<Integer> {

// The number to search

private int num;

private int[] array;

private int left;

private int right;

public Counter(int num, int[] array, int left, int right) {

this.num = num;

this.array = array;

this.left = left;

this.right = right;

}

/**

* Inherited from RecursiveAction.

* Compare it with the run method of a Thread.

*/

@Override

public Integer compute() {

if (left == right) {

// Check the number

if (array[left] == num) {

return 1;

}

} else if (left < right) {

int mid = (left + right) / 2;

// Create sub tasks

RecursiveTask<Integer> leftTask = new Counter(num, array, left, mid);

RecursiveTask<Integer> rightTask = new Counter(num, array, mid + 1, right);

// Execute the sub tasks

leftTask.fork();

rightTask.fork();

int count = 0;

// Wait and recieve the outputs from sub tasks

count += leftTask.join();

count += rightTask.join();

return count;

}

return 0;

}

}