CC上一道关于抽象类的设计问题

CC150 3.7 adopt The Oldest Animal

题目：

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An animal shelter holds only dogs and cats, and operates on a strictly "first in, first out" basis. People must adopt either the "oldest" (based on arrival time) of all animals at the shelter, or they can select whether they would prefer a dog or a cat (and will receive the oldest animal of that type). They cannot select which specific animal they would like. Create the data structures to maintain this system and implement operations such as enqueue, dequeueAny, dequeueDog and dequeueCat.You may use the built-in LinkedList data structure.



code：

1. code：
   
2. 1)Anima.java
   
3. package Question3_7;
   
4. public abstract class Animal
   
5. private int order ;
   
6. protected String name ;
   
7. public Animal(String name){
   
8. this.name =name;
   
9. 
   
10. }
    
11. 
    
12. public abstract String name();//抽象方法
    
13. 
    
14. public void setOrder(int order){
    
15. 
    
16. this.order =order;
    
17. }
    
18. 
    
19. public int getOrder(){
    
20. 
    
21. return order ;
    
22. 
    
23. }
    
24. 
    
25. 
    
26. public boolean isOlderThan(Animal a){
    
27. 
    
28. return this .order <a.getOrder();
    
29. 
    
30. }
    
31. 
    
32. }
    
33. 
    
34. 2）Cat.java
    
35. package Question3_7;
    
36. public class Cat extends Animal{
    
37. public Cat(String name){
    
38. 
    
39. super(name);
    
40. }
    
41. 
    
42. public String name(){
    
43. 
    
44. return "Cat: " +name ;
    
45. 
    
46. }
    
47. }
    
48. 
    
49. 3)Dog.java
    
50. package Question3_7;
    
51. public class Dog extends Animal{
    
52. public Dog(String name){
    
53. 
    
54. super(name);
    
55. }
    
56. 
    
57. public String name(){
    
58. 
    
59. return "Dog: " +name ;
    
60. 
    
61. }
    
62. }
    
63. 3)AnimalQueue.java
    
64. 
    
65. package Question3_7;
    
66. import java.util.LinkedList;
    
67. public class AnimalQueue{
    
68. LinkedList<Dog> dogs=new LinkedList<Dog>();
    
69. LinkedList<Cat> cats=new LinkedList<Cat>();
    
70. private int order ;
    
71. 
    
72. public void enqueue(Animal a){
    
73. a.setOrder(order);
    
74. order++;
    
75. 
    
76. if(a instanceof Dog) dogs .addLast((Dog) a);
    
77. else if (a instanceof Cat) cats.addLast((Cat) a);
    
78. 
    
79. 
    
80. }
    
81. 
    
82. public Animal dequeueAny(){
    
83. if(dogs .size()==0) {
    
84. 
    
85. return cats.poll();
    
86. 
    
87. }else if(cats .size()==0){
    
88. return dogs.poll();
    
89. 
    
90. }
    
91. 
    
92. Dog dog=dogs.peek();
    
93. Cat cat=cats.peek();
    
94. 
    
95. if(dog.isOlderThan(cat)){
    
96. 
    
97. return dogs.poll();
    
98. }else{
    
99. return cats.poll();
    
100. 
     
101. 
     
102. }
     
103. 
     
104. 
     
105. }
     
106. public Dog dequeueDog(){
     
107. 
     
108. return dogs .poll();
     
109. 
     
110. }
     
111. public Cat dequeueCat(){
     
112. 
     
113. return cats .poll();
     
114. 
     
115. }
     
116. }
     
117. 4)Question.java
     
118. package Question3_7;
     
119. 
     
120. public class Question {
     
121. 
     
122.    
     
123. 
     
124.     public static void main(String[] args){
     
125. AnimalQueue animals=new AnimalQueue();
     
126. animals.enqueue(new Cat( "Callie"));
     
127. animals.enqueue(new Cat( "Kiki"));
     
128. animals.enqueue(new Dog( "Fido"));
     
129. animals.enqueue(new Dog( "Dora"));
     
130. animals.enqueue(new Cat( "Kari"));
     
131. animals.enqueue(new Dog( "Dexter"));
     
132. animals.enqueue(new Dog( "Dobo"));
     
133. animals.enqueue(new Cat( "Copa"));
     
134. System.out.println(animals.dequeueAny().name());   
     
135. System.out.println(animals.dequeueAny().name());   
     
136. System.out.println(animals.dequeueAny().name());
     
137. System.out.println(animals.dequeueCat().name());
     
138. System.out.println(animals.dequeueDog().name());
     
139. }
     
140. }
     

复制代码

感觉这里实现多态没必要用抽象类啊，一般用抽象类实现多肽的好处是啥？