猫狗队列

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：
（1）用户可以调用add方法将cat类或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进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类的实例按照进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类的实例按照进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或cat的实例
（6）用户可以调用isDogEmpty方法，检查队列中是否有dog类的实例
（7）用户可以调用isCatEmpty方法，检查队列中是否有cat类的实例。

解题思路：设计一个类PetEnterQueue ，用于记录放入队列中的每个元素的时间戳count，取出时按时间戳来判断从dog队列还是cat队列取出元素。

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

public class DogCat {

    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; //时间戳

        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<>();
            this.catQ = new LinkedList<>();
            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("error, 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("error, 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(cat3);
        test.add(dog3);

        while (!test.isEmpty()){
            System.out.println(test.pollAll().getPetType());
        }
    }
}