猫狗队列

// 宠物类
public class Pet {

    private String mType;

    public Pet(String type) {
        mType = type;
    }

    public String getType() {
        return mType;
    }
}

// 狗
public class Dog extends Pet {

    public Dog(String type) {
        super(type);
    }
}

// 喵
public class Cat extends Pet {

    public Cat(String type) {
        super(type);
    }
}

public class PetWithTimestamp {

    private Pet mPet;

    private long mTimestamp;

    public PetWithTimestamp(Pet pet, long timestamp) {
        mPet = pet;
        mTimestamp = timestamp;
    }

    public Pet getPet() {
        return mPet;
    }

    public long getTimestamp() {
        return mTimestamp;
    }

    public String getType() {
        return mPet.getType();
    }
}

public class CatDogQueue {

    private Queue<PetWithTimestamp> mCatQueue;

    private Queue<PetWithTimestamp> mDogQueue;


    public CatDogQueue() {
        mCatQueue = new LinkedList<>();
        mDogQueue = new LinkedList<>();
    }

    public void add(Pet pet) {

        if (pet == null) {
            throw new IllegalArgumentException("pet can't be null");
        }

        switch (pet.getType()) {

            case "cat":
                mCatQueue.add(new PetWithTimestamp(pet, System.currentTimeMillis()));
                break;

            case "dog":
                mDogQueue.add(new PetWithTimestamp(pet, System.currentTimeMillis()));
                break;

            default:
                break;
        }
    }

    public Pet pollAll() {

        if (!mCatQueue.isEmpty() && !mDogQueue.isEmpty()) {

            if (mCatQueue.peek().getTimestamp() < mDogQueue.peek().getTimestamp()) {
                return mCatQueue.poll().getPet();
            } else {
                return mDogQueue.poll().getPet();
            }

        } else if (!mCatQueue.isEmpty()) {

            return mCatQueue.poll().getPet();

        } else if (!mDogQueue.isEmpty()) {

            return mDogQueue.poll().getPet();

        } else {
            throw new IllegalStateException("queue is empty!");
        }
    }

    public Cat pollCat() {
        if (!mCatQueue.isEmpty()) {
            return (Cat) mCatQueue.poll().getPet();
        } else {
            throw new IllegalStateException("dog queue is empty!");
        }
    }

    public Dog pollDog() {
        if (!mDogQueue.isEmpty()) {
            return (Dog) mDogQueue.poll().getPet();
        } else {
            throw new IllegalStateException("dog queue is empty!");
        }
    }
    
    public boolean isEmpty() {
        return mCatQueue.isEmpty() && mCatQueue.isEmpty();
    }

    public boolean isCatQueueEmpty() {
        return mCatQueue.isEmpty();
    }

    public boolean isDogQueueEmpty() {
        return mDogQueue.isEmpty();
    }

}