Same priority items in a priority queue

Question

Hello all,
I am writing a project that uses the PriorityQueue class to sort patients according to their emergency level.
The more urgent is a patient's condition, the higher the priority (Priority 1 = Very Urgent. Priority 10 = Not urgent).
However, there are many patients with the same priority and I would like to process them according to a first-in first-out scheme.
The PriorityQueue class doesn't seem to follow that scheme naturally.
Does anyone have an idea how to solve this problem?
Thanks in advance,
Nader

Answer 1

Thanks for the code. The compound parameter is instructive.
I'm not sure that you've thought it through, though. Declaring
public class OrderedPriorityQueue<T extends OpqComparator<T> & OpqOrderable<T>> extends PriorityQueue<T> { ...}forces an element to be declared
public class Foo extends OpqComparator<Foo>  implements OpqOrderable<Foo>  {...}and then you pass what as a comparator to the OPQ constructor? Apparently null because..
By having OpqOrderable extend Comparable as you suggest, the user is forced to write a compareTo() method. Assuming that he does so correctly, the 'natural ordering' of the class is sufficient to prevent ties. No comparator is needed.
By dropping the Comparable from OpqOrderable and using OpqComparator, the ordering due to the 'order' field is supplied, yet the user must still write essentially the same comparator code. Very little seems to have been achieved, although admittedly it's what I asked for. :) Am I missing something?
Here's what I have now:
public interface OpqOrderable<T> extends Comparable<T> {
     int getOrder();
     void setOrder( int order );
public class OrderedPriorityQueue<T extends OpqOrderable<T>> extends PriorityQueue<T> {
     public OrderedPriorityQueue( int initialCapacity ) {
          super(initialCapacity);
     @Override
    public boolean offer( T o ) {
          if( o instanceof OpqOrderable ) 
               synchronized (this)  {
                    o.setOrder( nextOrdinal++  );  }
        return offer(o);
public class Foo implements OpqOrderable<Foo>  {...}
private OrderedPriorityQueue<Foo> productionQueue = new OrderedPriorityQueue<Foo>( 100 );Thoughts?