Question

I am trying to use the priority queue, but the remove() is not working:
My code:

PriorityQueue<OwnClass> pq=new PriorityQueue<OwnClass>();
OwnClass a=new OwnClass(1);
OwnClass b=new OwnClass(2);
OwnClass c=new OwnClass(3);
pq.add(a);
pq.add(b);
pq.add(c);
System.out.println("head:"+pq.peek());
pq.remove(new OwnClass(1));
System.out.println(pq.peek());

And the class implementation:

class OwnClass implements Comparable{

    int x;

    public OwnClass(int x){
        this.x=x;
    }

    public int compareTo(Object arg0) {

        OwnClass a=(OwnClass) arg0;
        if(a.x>this.x)
            return -1;
        if(a.x<x)
            return 1;
        return 0;
    }

    public String toString(){
        return ""+x;        
    }
}

I think the output final output should be 2, since I am removing the added ‘1’. The compareTo() should be used by priority queue remove() but his does not seem to be the case. What I am doing wrong? I know pq.remove(a) will work, but then my code should also work

Answer 1

remove() will not use compareTo(), rather it will use equals() to find the object to remove. You need to override equals() on your class as well.

Edit: Javadoc for PriorityQueue (Thanks, @templatetypedef)