CODEWITHSUNDEEP
javadata-structurespriority-queuecomparator
Fox
Fox

Reputation: 9444

Errors using the Comparator interface

I am trying to write a simple application with priority queues. I am getting the following errors --" error: leastPriority is not abstract and does not override abstract method compare(Integer,Integer) in Comparator" and "error: incompatible types Comparator cmp = new leastPriority(); "

Can someone point out the problem with this code.

My code is : 

class leastPriority implements Comparator<Integer> {    
    public int compare(Reservation x, Reservation y){
        if(x.getPriority() > y.getPriority()){
            return -1;
        }
        if(x.getPriority() < y.getPriority()){
            return +1;
        }
        return 0;
    }
}

public class prioQueue{

    public static void main(String args[]){
        Comparator<Reservation> cmp = new leastPriority();
        PriorityQueue<Reservation> queue = new PriorityQueue<Reservation>(10,cmp);
        queue.add(new Reservation(1,"Andy",10));
        queue.add(new Reservation(1,"Peter",1));
        queue.add(new Reservation(1,"John",4));

        while(true){
            Reservation r = queue.poll();
            if(r==null){
                break;
            }
            System.out.println(r.getName());
        }

    }
}

Upvotes: 0

Views: 1519

Answers (2)

manub
manub

Reputation: 4100

leastPriority should implement Comparator<Reservation> instead of Comparator<Integer>. The generic type is the one that's accepted as a parameter in your compare() method.

P.S. It's a good practice to name all Java classes with a first uppercase letter (PrioQueue) and (LeastPriority).

Upvotes: 1

zw324
zw324

Reputation: 27220

Your type parameter for Comparator<T> and your compare(T o1, T o2) method's parameters does not match. Since in the interface they are the same, you need to give identical types to them.

Change this:

class leastPriority implements Comparator<Integer>

to:

class leastPriority implements Comparator<Reservation>

Upvotes: 7

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