Implemeting a priority queue

Question

Hi all,
i have written a priority queue which implements a priority queue interface however i'm getting a liitle stuck. I'm pretty new to Java programming, i'm trying to write a hosptial simulation where ill people arrive and are given a priority to be seen by a medic.
Every patient that is added to the queue has an int prioriy and the patient that is serviced next is the one with the highest priority. There are three priorities, low, medium, high. If more than one patient has the same highest priority, the patient with that priority that has been longest in the queue will be serviced.
Could you please help me out to see where my mistakes are?
Thanks
The priority queue interface
import java.util.Iterator;
public interface PriorityQueue
* Adds element to the priority queue
* @param element - the element to be added to the queue.
public void add (Priority element);
* Removes the next element from the priority queue
* Precondition: size() != 0
public void remove ();
* The next element to be serviced. This is the element in the queue that has
* the highest priority. If more than one element has the highest priority,
* the one which was added to the queue earliest is returned.
* Note that this has no effect on the queue - you must call remove as well to
* change the queue state.
* Precondition: size() != 0
* @return the next element to be serviced.
public Priority next();
* @return the number of elements in the priority queue
public int size();
* @return an Iterator for the priority queue.
public Iterator iterator
The priority queue
import java.util.ArrayList;
import java.util.Iterator;
public class PriorityQueueImpl implements PriorityQueue
private final static int DEFAULT_PRIORITY_COUNT = 3;
private ArrayList elements = new ArrayList();
public void add (Priority element)
elements.add (element);
public void remove ()
Iterator it = elements.iterator();
it.remove();
public Priority next()
Iterator it = elements.iterator();
Priority p, highestPriority;
while (it.hasNext())
p = it.next();
if (p.priority > highestPriority.priority)
highestPriority = p;
else if (p.priority == highestPriority.priority &&
p.admissionTime < highestPriority.admissionTime)
highestPriority = p;
public Iterator iterator()
Iterator it = new Iterator()
int size = size();
int priority = priority;
return it;
public int size()
int size = 0;
if (queue[i] !=null)
size += queue.size();
return size;

Answer 1

Hi there,
I guess you are on the Herts uni course like myself, right? Have you had any luck with getting this to work, or are you still stuck like me?!
cheers
Matt Brett