猫狗队列问题

猫狗队列 【题目】 宠物、狗和猫的类如下：
public class Pet { private String type;
public Pet(String type) { this.type = type; }
public String getPetType() { return this.type; }
}
public class Dog extends Pet { public Dog() { super("dog"); } }
public class Cat extends Pet { public Cat() { super("cat"); } }
实现一种狗猫队列的结构，要求如下：

用户可以调用add方法将cat类或dog类的实例放入队列中；

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

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

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

用户可以调用isEmpty方法，检查队列中是否还有dog或cat的实例；

用户可以调用isDogEmpty方法，检查队列中是否有dog类的实例；

用户可以调用isCatEmpty方法，检查队列中是否有cat类的实例；

import java.util.LinkedList;
import java.util.Queue;

public class DogCatQueue {

	public static class Pet {
		private String type;

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

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

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

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

	public static class PetEnterQueue {
		private Pet pet;
		private long count;

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

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

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

		public String getEnterPetType() {
			return this.pet.getPetType();
		}
	}

	public static class DogCatQueue {
		private Queue<PetEnterQueue> dogQ;
		private Queue<PetEnterQueue> catQ;
		private long count;

		public DogCatQueue() {
			this.dogQ = new LinkedList<PetEnterQueue>();
			this.catQ = new LinkedList<PetEnterQueue>();
			this.count = 0;
		}

		public void add(Pet pet) {
			if (pet.getPetType().equals("dog")) {
				this.dogQ.add(new PetEnterQueue(pet, this.count++));
			} else if (pet.getPetType().equals("cat")) {
				this.catQ.add(new PetEnterQueue(pet, this.count++));
			} else {
				throw new RuntimeException("err, not dog or cat");
			}
		}

		public Pet pollAll() {
			if (!this.dogQ.isEmpty() && !this.catQ.isEmpty()) {
				if (this.dogQ.peek().getCount() < this.catQ.peek().getCount()) {
					return this.dogQ.poll().getPet();
				} else {
					return this.catQ.poll().getPet();
				}
			} else if (!this.dogQ.isEmpty()) {
				return this.dogQ.poll().getPet();
			} else if (!this.catQ.isEmpty()) {
				return this.catQ.poll().getPet();
			} else {
				throw new RuntimeException("err, queue is empty!");
			}
		}

		public Dog pollDog() {
			if (!this.isDogQueueEmpty()) {
				return (Dog) this.dogQ.poll().getPet();
			} else {
				throw new RuntimeException("Dog queue is empty!");
			}
		}

		public Cat pollCat() {
			if (!this.isCatQueueEmpty()) {
				return (Cat) this.catQ.poll().getPet();
			} else
				throw new RuntimeException("Cat queue is empty!");
		}

		public boolean isEmpty() {
			return this.dogQ.isEmpty() && this.catQ.isEmpty();
		}

		public boolean isDogQueueEmpty() {
			return this.dogQ.isEmpty();
		}

		public boolean isCatQueueEmpty() {
			return this.catQ.isEmpty();
		}

	}

	public static void main(String[] args) {
		DogCatQueue test = new DogCatQueue();

		Pet dog1 = new Dog();
		Pet cat1 = new Cat();
		Pet dog2 = new Dog();
		Pet cat2 = new Cat();
		Pet dog3 = new Dog();
		Pet cat3 = new Cat();

		test.add(dog1);
		test.add(cat1);
		test.add(dog2);
		test.add(cat2);
		test.add(dog3);
		test.add(cat3);

		test.add(dog1);
		test.add(cat1);
		test.add(dog2);
		test.add(cat2);
		test.add(dog3);
		test.add(cat3);

		test.add(dog1);
		test.add(cat1);
		test.add(dog2);
		test.add(cat2);
		test.add(dog3);
		test.add(cat3);
		while (!test.isDogQueueEmpty()) {
			System.out.println(test.pollDog().getPetType());
		}
		while (!test.isEmpty()) {
			System.out.println(test.pollAll().getPetType());
		}
	}

}