问在Java中使用多线程并行快速排序

EN

import java.util.Arrays;
import java.util.Random;


public class QuickSort {


public synchronized static int pivot(int[] a, int lo, int hi){
    int mid = (lo+hi)/2;
    int pivot = a[lo] + a[hi] + a[mid] - Math.min(Math.min(a[lo], a[hi]), a[mid]) - Math.max(Math.max(a[lo], a[hi]), a[mid]);

    if(pivot == a[lo])
        return lo;
    else if(pivot == a[hi])
        return hi;
    return mid;
}

public synchronized static int partition(int[] a, int lo, int hi){

    int k = pivot(a, lo, hi);
    //System.out.println(k);
    swap(a, lo, k);
    //System.out.println(a);
    int j = hi + 1;
    int i = lo;
    while(true){

        while(a[lo] < a[--j])
            if(j==lo)   break;

        while(a[++i] < a[lo])
            if(i==hi) break;

        if(i >= j)  break;
        swap(a, i, j);
    }
    swap(a, lo, j);
    return j;
}

public synchronized static void sort(int[] a, int lo, int hi){
    if(hi<=lo)  return;
    int p = partition(a, lo, hi);
    Thread t1=new Thread(new Runnable(){

        @Override
        public void run() {

            sort(a, lo, p-1);
        }

    });
    Thread t2=new Thread(new Runnable(){
        public void run()
        {
            sort(a, p+1, hi);
        }
    });
    t1.start();
    t2.start();
    try {
        t1.join();
        t2.join();
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

public synchronized static  void swap(int[] a, int b, int c){
    int swap = a[b];
    a[b] = a[c];
    a[c] = swap;
}

public synchronized static void sort(int[] a){
    sort(a, 0, a.length - 1);
    System.out.print(Arrays.toString(a));
}

public static void main(String[] args) {
    int arr[] = new int[1001];
    Random rand=new Random();
    for(int i=0;i<1000;i++)
    {
        arr[i]=rand.nextInt(350);

    }
    float start=System.currentTimeMillis();
    sort(arr);
    float end=System.currentTimeMillis();
    System.out.println("Time take to sort");
    System.out.println(end-start);
 }
}