Scala vs Java : Implementing quicksort -- not optimized

Below is an implementation of a quicksort the java way

void sort(int[] xs) {
 sort(xs, 0, xs.length -1 );
}
void sort(int[] xs, int l, int r) {
 int pivot = xs[(l+r)/2];
 int a = l; int b = r;
 while (a <= b)
   while (xs[a] < pivot) { a = a + 1; }
   while (xs[b] > pivot) { b = b – 1; }
   if (a <= b) {
     swap(xs, a, b);
     a = a + 1;
     b = b – 1;
   }
 }
 if (l < b) sort(xs, l, b);
 if (b < r) sort(xs, a, r);
}
void swap(int[] arr, int i, int j) {
 int t = arr[i]; arr[i] = arr[j]; arr[j] = t;
}
Quicksort the scala way ... looks neater and is easier to understand

object QuickSort {
 def sort(xs:Array[Int]):Array[Int]={
    if(xs.length<1)xs
                  else{
                    val pivot=xs(xs.length/2)
                    Array.concat(
                        sort(xs filter (pivot >)),
                          xs filter (pivot ==),
                        sort(xs filter (pivot <)))
                  }
       }
}