implementing quick sort

Sorting/QuickSorter.java

@@ -4,11 +4,31 @@ public class QuickSorter extends Sorter{
     
     public QuickSorter(String filename){
         super("quick", filename);
-        System.out.println("This is stub code, to be removed");
     }
 
     void sort(){
+        quickSort(0,numbers.length-1);
+    }
 
+    private void quickSort(int lowIndex, int highIndex){
+       if(lowIndex<highIndex){
+            int pivot = partition(lowIndex, highIndex);
+            quickSort(lowIndex, pivot-1);
+            quickSort(pivot+1, highIndex);
+       }
+    }
+
+    private int partition(int lowIndex, int highIndex){
+        int pivot = numbers[highIndex];
+        int i = lowIndex-1;
+        for(int j=lowIndex;j<highIndex;j++){
+            if(numbers[j]<pivot){
+                i++;
+                swap(i,j);
+            }
+        }
+        swap(i+1, highIndex);
+        return i+1;
     }
 
 }