一、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 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,检查队列中是否还有dog类的实例;
(7)用户可以调用isCatEmpty方法,检查队列中是否还有cat类的实例。
二、解答
实现思路我们其实是想把每次进入队列的实例都加上时间戳的方法,但不能改变原有的数据结构,所以只能定义一个新类来封装时间戳,具体实现如下PetEnterQueue类:
public 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(); } }
上述代码中的count就是我们加上的时间戳。队列里存放的就是PetEnterQueue实例。
DogCatQueue类的整体代码如下:
import java.beans.PersistenceDelegate; import java.util.LinkedList; import java.util.Queue; public 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, 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("err,queue is empty"); } } public Dog polldog() { if(!this.dogQ.isEmpty()) { return (Dog)this.dogQ.poll().getPet(); }else { throw new RuntimeException("Dog Queue is empty!"); } } public Cat pollcat() { if(!this.catQ.isEmpty()) { 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(); } }