Quick sort problem

[fishy8158]

the professor wrote a quick sort algorithm on the board and just told us to copy and read it at home. How ever it didn't run and i tried my best to learn it online and fix the code but it still doesn't seem to run, or im misunderstanding quick sort.

public class QuickSort{
	public QuickSort(int[] anArray){
		a=anArray;
	}
public void sort(int from,int to){
	if(from>=to) return;
	int p=partition(from,to);
	sort(from,to);
	sort(p+1,to);
	}
private int partition(int from,int to){
	int pivot=a[from];
	int j=to+1;
	int i=from;
	while(i<j){
		i++;
		while(a[i]<pivot)i++;
			j--;
			while(a[j]>pivot)j--;
			if(i<j)
				swap(i,j);
		}
		return j;
	}
	private void swap(int i,int j){
		int temp=a[i];
		a[i]=a[j];
		a[j]=temp;
	}
private int[] a;
}

public class QuickSortTester {
	public static void main(String args[]){
		ArrayUtil au=new ArrayUtil();
		int[] a=au.randomIntArray(20, 100);
		QuickSort qs=new QuickSort(a);
		qs.sort(0,19); //2 random numbers i put, cuz i don't understand it.
		au.print(a);
		}
	}
}

If anyone can point out where its wrong, that will be great. Thanks in advance.