java - Quicksort partitioning -

i have following array:

int[] arr = { 19, 4, 2, 3, 9, 2, 10, 2, 7, 12, 5, 16, 8, 3, 11, 14, 0, 5 }; 

and use quicksort's partitioning partition array pivot element 7:

    public static void partition(int[] arr, int low, int high) {     int pivot = arr[low + (high - low) / 2];     int = low;     int j = high;     while (i <= j) {         // if current value left list smaller pivot         // element next element left list         while (arr[i] < pivot) {             i++;         }         // if current value right list larger pivot         // element next element right list         while (arr[j] > pivot) {             j--;         }          // if have found values in left list larger         // pivot element , if have found value in right list         // smaller pivot element exchange         // values.         // done can increase , j         if (i <= j) {             swap(arr, i, j);             i++;             j--;         }     } } 

i confused outcome:

5 4 2 3 0 2 3 2 5 12 7 16 8 10 11 14 9 19  

i thought every element <= pivot (7) must left , every element > pivot element must on right. why 12 left 7 ?

this implementation cannot guarantee expect. following (provided change arr[i] <= pivot, achintya jha suggested, otherwise can't guarantee that):

for every pair of values a, b a <= pivot < b, guaranteed a left of b in end. however, don't guarantee anything exact position of pivot in final array (only it's left of values larger).