请用java写一段快速排序算法的代码

public class QuickSort {

public static void main(String[] args) { int[] arr = { 5, 2, 9, 1, 5, 6 };

quickSort(arr, 0, arr.length - 1);

for (int i = 0; i < arr.length; i++) {
  System.out.print(arr[i] + " ");
}

}

public static void quickSort(int[] arr, int left, int right) { if (left >= right) { return; }

int pivot = arr[(left + right) / 2];
int index = partition(arr, left, right, pivot);

quickSort(arr, left, index - 1);
quickSort(arr, index, right);

}

public static int partition(int[] arr, int left, int right, int pivot) { while (left <= right) { while (arr[left] < pivot) { left++; }

  while (arr[right] > pivot) {
    right--;
  }
  
  if (left <= right) {
    int temp = arr[left];
    arr[left] = arr[right];
    arr[right] = temp;
    left++;
    right--;
  }
}

return left;

}