From http://www.vogella.com/tutorials/JavaAlgorithmsQuicksort/article.html

QuickSort array java

package de.vogella.algorithms.sort.quicksort;


public class Quicksort  {
        private int[] numbers;
        private int number;

        public void sort(int[] values) {
                // check for empty or null array
                if (values ==null || values.length==0){
                        return;
                }
                this.numbers = values;
                number = values.length;
                quicksort(0, number - 1);
        }

        private void quicksort(int low, int high) {
                int i = low, j = high;
                // Get the pivot element from the middle of the list
                int pivot = numbers[low + (high-low)/2];

                // Divide into two lists
                while (i <= j) {
                        // If the current value from the left list is smaller than the pivot
                        // element then get the next element from the left list
                        while (numbers[i] < pivot) {
                                i++;
                        }
                        // If the current value from the right list is larger than the pivot
                        // element then get the next element from the right list
                        while (numbers[j] > pivot) {
                                j--;
                        }

                        // If we have found a value in the left list which is larger than
                        // the pivot element and if we have found a value in the right list
                        // which is smaller than the pivot element then we exchange the
                        // values.
                        // As we are done we can increase i and j
                        if (i <= j) {
                                exchange(i, j);
                                i++;
                                j--;
                        }
                }
                // Recursion
                if (low < j)
                        quicksort(low, j);
                if (i < high)
                        quicksort(i, high);
        }

        private void exchange(int i, int j) {
                int temp = numbers[i];
                numbers[i] = numbers[j];
                numbers[j] = temp;
        }
}