QuickSort Problems

Question

I am trying to write a QuickSort to sort an ArrayList of random integers passed from another class. If it is given 5 2 7 6 9 0 8 1 3 4 it finishes with the ArrayList holding 0 1 2 4 3 5 7 6 8 9
is this a problem with my logic or just a minor programming error? I am using the first item in the ArrayList as the pivot, partitioning, and then swapping the pivot into position and recursively running quicksort(start,pivot-1) and quicksort(pivot+1,end)
import java.util.*;
public class QuickSort
ArrayList<Integer> data;
public QuickSort(ArrayList<Integer> datax)
data=datax;
public void quicksort(int start, int end)
if (start < end)
int pivot = partition(start, end);
quicksort(start, pivot-1);
quicksort(pivot+1, end);
public int partition(int start, int end)
int pivot = data.get(start);
int l = start + 1;
int r = end;
while (l < r)
while (l < end && data.get(l) < pivot) l++;
while (r > start && data.get(r) >= pivot) r--;
if (l < r)
swap(l,r);
swap(start,r);
return r;
public void swap(int index1, int index2)
int temp=data.get(index1);
data.set(index1,data.get(index2));
data.set(index2,temp);
}

Answer 1

What happens when your partition method is passed a range that contains two numbers that are already sorted?