Why do I get this error message?

Question

I'm trying to make a recursive quick sort that has a pivot in the middle of the array, instead of the beginning.
I thought by dividing the end by half and making it an int would give me a number that would allow me to make the pivot the middle number.
But when I try running this (it compiles fine), I keep getting a StackOverflowError.
I'm still confused about recursions, and maybe that's why I don't get what I'm doing wrong.
Would someone please help me understand why I get a StackOverflowError?
Thank you so much.
This code is just for the dividing the array into 2 parts, with the pivot in the middle.
I get the StackOverflowError at the first line "int n = (int)(end/2);"
private static int partition (int[] numbers, int start, int end)
      int n = (int)(end/2);
      int pivot = numbers[n];
      int i = n - 1;
      int j = end + 1;
      while (true)
         i = i + 1;
         while (numbers[i] < pivot)
            i = i + 1;
         j = j - 1;
         while (numbers[j] > pivot)
            j = j - 1;
         if (i < j)
            int tmp = numbers;
numbers[i] = numbers[j];
numbers[j] = tmp;
else return j;
i = start - 1;
j = n + 1;
i = i + 1;
while (numbers[i] < pivot)
i = i + 1;
j = j - 1;
while (numbers[j] > pivot)
j = j - 1;
if (i < j)
int tmp = numbers[i];
numbers[i] = numbers[j];
numbers[j] = tmp;
else return j;

Answer 1

Oh. I've only put the coding that would partition the array.
This would call it.
private static void doQuickSort (int[] numbers, int start, int end)
      if (start < end)
         int middle = partition(numbers, start, end);
         doQuickSort(numbers, start, middle);
         doQuickSort(numbers, middle, end);
   }