猫狗队列

 实现一种猫狗队列的结构，要求如下： 

1 用户可以调用add方法将cat类或者dog类的实例放入队列中；

2 用户可以调用pollAll方法，将队列中所有的实例按照队列的先后顺序依次弹出；

3 用户可以调用pollDog方法，将队列中dog类的实例按照队列的先后顺序依次弹出；

4 用户可以调用pollCat方法，将队列中cat类的实例按照队列的先后顺序依次弹出；

5 用户可以调用isEmpty方法，检查队列中是否还有dog和cat的实例；

6 用户可以调用isDogEmpty方法，检查队列中是否还有do的实例；

7 用户可以调用isCatEmpty方法，检查队列中是否还有cat的实例

public class CatAndDogQueue {

    private Queue<PetEntry> catQueue = new LinkedList<PetEntry>();
    private Queue<PetEntry> dogQueue = new LinkedList<PetEntry>();
    private long count = 0;

    public void add(Pet pet) {
        if (pet.getType().equals("Dog")) {
            this.dogQueue.add(new PetEntry(pet, this.count++));
        } else if (pet.getType().equals("Cat")) {
            this.catQueue.add(new PetEntry(pet, this.count++));
        } else {
            throw new RuntimeException("error! input not dog or cat!");
        }

    }

    public Pet popDog() {
        if (!dogQueue.isEmpty()) {
            return dogQueue.poll().getPet();
        } else {
            throw new RuntimeException("DogQueue is Empty");
        }
    }

    public Pet popCat() {
        if (!catQueue.isEmpty()) {
            return catQueue.poll().getPet();
        } else {
            throw new RuntimeException("DogQueue is Empty");
        }
    }

    public Pet popAll() {
        if (!catQueue.isEmpty() && !dogQueue.isEmpty()) {
            if (catQueue.peek().getCount() < dogQueue.peek().getCount()) {
                return catQueue.poll().getPet();
            } else {
                return dogQueue.poll().getPet();
            }
        } else if (!catQueue.isEmpty()) {
            return catQueue.poll().getPet();
        } else if (!dogQueue.isEmpty()) {
            return dogQueue.poll().getPet();
        } else {
            throw new RuntimeException("err! queue is empty");
        }
    }

    public boolean isEmpty() {
        return dogQueue.isEmpty() && catQueue.isEmpty();
    }

    public boolean isDogEmpty() {
        return dogQueue.isEmpty();
    }

    public boolean isCatEmpty() {
        return catQueue.isEmpty();
    }

}

class PetEntry {
    private Pet pet;
    private long count;

    public PetEntry(Pet pet, long count) {
        this.pet = pet;
        this.count = count;
    }

    public Pet getPet() {
        return this.pet;
    }

    public long getCount() {
        return this.count;
    }

    public String getEntryPetType() {

        return this.pet.getType();
    }
}

class Pet {
    private String type;

    public Pet(String type) {
        this.type = type;
    }

    public String getType() {
        return this.type;
    }
}

class Dog extends Pet {
    public Dog() {
        super("Dog");
    }
}

class Cat extends Pet {
    public Cat() {
        super("Cat");
    }
}