Question

I currently have a class that has 3 linkedlists of strings or ints that I use as a stack via a trio of addFirst and removeFirst commands. (Class reproduced below)

I want to add the ability to use the class as a priority queue instead. I know what a priority queue is, so I’m looking for a simple way to add insertWithPriority and removeNext.

The intuitive option is to switch from a class of 3 linkedLists to 3 priorityQueues instead, but I’m a little confused how to use the priority queues in java. Specifically, I need priority for all 3 to function identically such that removeNext will remove the same 3 elements that were added by insertWithPriority.

Could someone shed some light on how to implement a proper priorityQueue?

class ThreeList{
    public LinkedList foo;
    public LinkedList bar;
    public LinkedList etal;

    public ThreeList(){
        foo= new LinkedList();
        bar= new LinkedList();
        etal= new LinkedList();
    }

    public void addLast(String foo, int bar, int etal){
        foo.addLast(foo);
        bar.addLast(bar);
        etal.addLast(etal);
    }

    public void addFirst(String foo, int bar, int etal){
        foo.addFirst(foo);
        bar.addFirst(bar);
        etal.addFirst(etal);
    }

    public void removeFirst(){
        foo.removeFirst();
        bar.removeFirst();
        etal.removeFirst();
    }

    public void removeLast(){
        foo.removeLast();
        bar.removeLast();
        etal.removeLast();
    }   
}

Answer 1

PriorityQueue offers priorization by use of Comparable or Comparator, i.e. you only use add.

In your case it would be best to use a simple static inner class to capture foo, bar and etal into one object.

static class FooBar implements Comparable<FooBar> {
   String foo;
   int bar, etal;

   int compareTo(FooBar other) {
     ... comparison logic here...
   }

}

If the values foo,bar,etal don’t implicitly contain a priority, you need to add another field to FooBar and use that in compareTo.