CC3.7.java

public class AnimalSehelter {
    private int id;
    private Queue<Cat> Cats;
    private Queue<Dog> Dogs;
    
    public AnimalSehelter() {
        this.id = 1;
        this.Cats = new LinkedList<Cat>();
        this.Dogs = new LinkedList<Dog>();
    }
    
    public void enqueue(Animal animal) {
        animal.setID(this.id++);
        if (animal instanceof Cat) {
            this.Cats.add((Cat) animal);
        }
        if (animal instanceof Dog) {
            this.Dogs.add((Dog) animal);
        }
    }
    
    public Animal dequeueAny() {
        if (Cats.isEmpty())
            return dequeueDog();
        if (Dogs.isEmpty())
            return dequeueCat();
        if (Cats.peek().id < Dogs.peek().id)
            return dequeueCat();
        else
            return dequeueDog();
    }
    
    public Cat dequeueCat() {
        if (Cats.isEmpty())
            throw new NoSuchElementException("queue underflow!");
        return Cats.poll();
    }
    
    public Dog dequeueDog() {
        if (Dogs.isEmpty())
            throw new NoSuchElementException("queue underflow!");
        return Dogs.poll();
    }
}

class Animal {
    int id;
    public void setID(int id) {
        this.id = id;
    }
}

class Cat extends Animal {
    
}

class Dog extends Animal {
    
}