Parallel Search

Problem:

Write a Java class that allows parallel search in an array of integer. It provides the following static method:

public static int parallelSearch(int[ ] a , int numThreads)

This method creates as many threads as specified by numThreads, divides the array a into that many parts, and gives each thread a part of the array to search for sequentially. If any thread finds x, then it returns an index i such that A [ i ] = x. Otherwise, the method returns -1.

Solution:

package org.zero.concurrent.chap01;

import java.util.Arrays;

public class ParallelSearch {
    private static int index = -1;

    public static int parallelSearch(int search, int[] in, int numThreads) {
        // partition
        int partitionSize = in.length / numThreads;
        Thread[] threads = new Thread[numThreads];
        int end = 0;
        int begin = 0;
        // search
        for (int i = 0; i < numThreads; i++) {
            end = begin + partitionSize;
            if (i == numThreads - 1 || end > in.length) {
                end = in.length;
            }
            Search target = new Search(begin, end, in, search);
            System.out.println(target);
            threads[i] = new Thread(target);
            threads[i].start();
            System.out.println(threads[i].getName());
            begin = end;
        }
        return index;
    }

    public static void main(String[] args) {
        int[] a = new int[100];
        for (int i = 0; i < a.length; i++) {
            a[i] = (int) (Math.random() * 10);
        }
        int parallelSearch = parallelSearch(2, a, 7);
        if (-1 == parallelSearch) {
            System.out.println("not found");
        } else {
            System.out.println("found at: " + parallelSearch);
        }
    }

    private static class Search implements Runnable {
        int begin;
        int end;
        int[] a;
        int x;

        public Search(int begin, int end, int[] a, int x) {
            super();
            if (end < begin) {
                throw new IllegalStateException();
            }
            this.begin = begin;
            this.end = end;
            this.a = a;
            this.x = x;
        }

        @Override
        public void run() {
            for (int i = begin; i < end; i++) {
                if (x == a[i]) {
                    index = i;
                    System.out.println(i + " "
                            + Thread.currentThread().getName());
                    // break;
                }
            }
        }

        @Override
        public String toString() {
            return "Search [a=" + Arrays.toString(a) + ", length=" + a.length
                    + ", begin=" + begin + ", end=" + end + ", x=" + x + "]";
        }

    }
}

P.S: Any suggestion to improve the code is welcome.