Java PriorityQueue 比较器

Question

Say that I have an shoeCollection class that has both the shoe size and the shoe brand. how do I modify the comparator such that it will sort the priorityQueue based on shoe size?

I know that priority queues already have a build-in comparator, but since my object is not an Integer or Double, I figured I need to write my own.

This is my comparator right now

static class ShoeComparator implements Comparator<shoes>
{
    @Override
    public int compare(shoes x, shoes y)
    {
        if(x.getID() > y.getID()){
            return 1;
        }
        if(x.getID() < y.getID()){
            return -1;
        }
        return 0;
    }
}

I then declare a new Shoe priority queue with the following

private static Comparator<shoes> comparator = new shoeComparator();
private static PriorityQueue<shoes> list = new PriorityQueue<shoes>(10001, comparator);

I tried adding some shoes and see how it will turn out

    list.add(new shoes(56.0, "Nike"));
    list.add(new shoes(47.0, "Addidas"));
    list.add(new shoes(93.0, "Puma"));
    list.add(new shoes(3.0, "Vans"));

Test it in Main

for(int i = 0; i < list.size(); i++){
        System.out.println(list.poll().getID());

    }

//3.0 47.0

Only ID with 3.0 and 47.0 has been registered. Is there something wrong with my Comparator?

It seems like it will only return the first 2 ID and ignore the rest, but when I call upon list.size() it returns 4, which is correct. I can't locate the problem.

Answer 1

You can create the PriorityQueue and in the constructor put comparator code.

Example:

PriorityQueue<Integer> priorityQueue = new PriorityQueue<Integer>(10, new Comparator<Integer>()
{
    @Override
    public int compare(Integer o1, Integer o2)
    {
        // Logic here
        return 0;
    }
});

Answer 2

You can create a custom comparator inline during PriorityQueue instantiation.

Assuming your Shoe class looks like the following:

public class Shoe {
    private double size;
    private String brand;

    public Shoe(double size, String brand) {
        this.size = size;
        this.brand = brand;
    }

    public double getSize() {
        return size;
    }
}

You can create a PriorityQueue that orders the shoes by size by doing the following:

PriorityQueue<Shoe> shoePQ = new PriorityQueue<>(10000, new Comparator<Shoe>() {
    @Override
    public int compare(Shoe s1, Shoe s2) {
        return s1.getSize()-s2.getSize();
    });
}

This will order the shoes smallest to largest. If you wanted the reverse order, you would replace the body of compare() with return s2.getSize()-s1.getSize();