Working with Queues

Question

Hi,
Im in a programming class right now and I am trying to use a Queue and PriorityQueue. The book i am useing say's that i should be using the "enqueue()" and "dequeue()" operators, but after looking it up on www.google.com i only found "offer()" and "remove()" I need to be able to set the priority of each of the items that i am putting into the queue but cant find anything that will let me do that. for instance i need a Sophmore to have a priority of 1 and a Junior to havea priority of 2 and a Senior to have a priority of 3. (Probably a classic example) What kind of queue would i use to do this? and what would i need to import and what operators can i use. I have spent a lot time search for it and cant find the answer, thanks.. any help is welll helpfull
Cobbweb

Answer 1

I don't know what book you are using but the PriorityQueue class doesn't have enqueue() and dequeue() methods. The methods are offer() and remove(). Now if you want to specify an ordering (a priority), you have to use the following constructor:
PriorityQueue(int initialCapacity, Comparator<? super E> comparator) which means that you'll need to implement a Comparator. The comparator interface has one method you need to implement:
int compare(T o1, T o2) Your compare method should -1 if o1 is less than o2, 0 if o1equals 02 and 1 if 01 is greater 02. For example if 01 is a junior and 02 is a sophmore, you return 1.
If your not familiar with generics, you may be panicking at the sight of the constructor. Essentially all you need to do is create a class, declare that it implements Comparator and include a compare method like:
int compare (Object o1, Object 02) {
    // you'll have to cast each Object to a Student class or whatever you're using
    // before trying to compare them
}Once you have this class created, say it's called MyComparator, you would construct your priority queue (I'm using 100 here for initial capacity - use whatever you want):
PriorityQueue theQueue = PriorityQueue(100, new MyComparator());