java的递归任务和分治算法实现大数组数据求和

package june.shen;

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveTask;

class work {
    static ForkJoinPool fjPool = new ForkJoinPool();
}

@SuppressWarnings("serial")
class ArraySum extends RecursiveTask<Long> {
    static final int min_unit = 100;//最小的划分结束单元，单元内部用串行方式执行

    int low;
    int high;
    int[] array;

    ArraySum(int[] arr, int lo, int hi) {
        array = arr;
        low   = lo;
        high  = hi;
    }

    protected Long compute() {
        if(high - low <= min_unit) {
            long sum = 0;
            for(int i=low; i < high; ++i) 
                sum += array[i];
            return sum;
         } else {
            int mid = low + (high - low) / 2;
            ArraySum left  = new ArraySum(array, low, mid);//划分为左右两部分
            ArraySum right = new ArraySum(array, mid, high);
            left.fork();//左边开始
            long rightRes = right.compute();//右边开始
            long leftRes  = left.join();
            return leftRes + rightRes;//合并两边的结果
         }
     }

     static public long sum(int[] a) {
         return work.fjPool.invoke(new ArraySum(a,0,a.length));//启动一个分治求和的线程池
     }
}

package june.shen;


import java.util.Random;


public class ArraySumTest {


public static void main(String[] args) {
// TODO Auto-generated method stub
int[] testArray=new int[100000];
for(int i=0;i<100000;i++)
{
Random ran = new Random();
testArray[i] = ran.nextInt(1000);
}

System.out.println(ArraySum.sum(testArray));
}


}