Quick sort in Java

Quick sort in Java

// Comment Quick Sort
 


 public static void quick_sort(int[] a) {
  int len = a.length;

  if (a == null || len == 0)
   throw new IllegalArgumentException("Null/Invalid Input");

  quick_sortUtil(a, 0, len - 1);

 }

 private static void quick_sortUtil(int[] a, int l, int r) {

  if (l > r)
   return;

  int p = pivot(a, l, r);
  quick_sortUtil(a, l, p - 1);
  quick_sortUtil(a, p + 1, r);

 }

 private static int pivot(int[] a, int l, int r) {

  int x = a[r], j, i;
  for (i = l, j = l; i < r && j < r; i++) {
   if (a[i] <= x) {
    swapArr(a, i, j);
    j++;
   }
  }

  swapArr(a, j, r);

  return j;
 }

 private static void swapArr(int[] arr, int i, int j) {
  int tmp = arr[i];
  arr[i] = arr[j];
  arr[j] = tmp;
 }