java - 将常量分配给对象

Question

我有一个抽象类 Animal，它有几个子类，例如 Dog、Cat 和 Rabbit。

每个子类都使用 Animal 类的构造函数，但子类中的每个对象也应该需要这样的常量。 Dog 对象应始终具有animalNumber = 1，并且每个Dog 对象应具有maximumNumberOfAnimals = 5 属性。但每个Cat 对象应始终具有animalNumber = 2，并且每个Cat 对象应具有maximumNumberOfAnimals = 10 属性。

我该如何编码？

这是我到目前为止所拥有的:

这是父类(super class):

public abstract class Animal {
private int weight;
private int height;

public Animal (int weight, int height) {
setWeight(weight);
setHeight(height);
}

public int getWeight() {
    return weight;
}
public void setWeight(int weight) {
     this.weight = weight;
}

public int getHeight() {
    return height;
}

public void setHeight(int height) {
    this.height = height;
}
}

这是一个子类

public class Dog extends Animal {

public static final int ANIMALNUMBER= 1;
public static final int MAXIMUMNUMBERALLOWED= 5;

//the constructor
public Dog (int weight, int height, int animalNumber, int maximumNumberAllowed) {
    super(weight, height)
    Dog.animalNumber = ANIMALNUMBER;
    Dog.maximumNumberAllowed = MAXIMUMNUMBERALLOWED;
}
}

这是另一个子类

public class Cat extends Animal {

public static final int ANIMALNUMBER= 2;
public static final int MAXIMUMNUMBERALLOWED= 10;

//the constructor
public Cat (int weight, int height, int animalNumber, int maximumNumberAllowed) {
    super(weight, height)
    Cat.animalNumber = ANIMALNUMBER;
    Cat.maximumNumberAllowed = MAXIMUMNUMBERALLOWED;
}
}

我最终想要的是这样的:

如果我使用 Dog Lassie = new Dog(40, 60, 1, 5) 调用构造函数来创建一个新的“Dog”。但我不应该被允许这样做: Dog Lassie = new Dog(40, 60, 2, 10)所以对于每只狗，ANIMALNUMBER应该是1，对于每只猫，ANIMALNUMBER应该是2。它是一个实例变量，但是该类的每个实例都应该相同。

这不仅说明:最终字段 Dog.ANIMALNUMBER 无法分配但我也认为这是行不通的。有什么建议吗？

提前致谢!

Answer 1

So for every Dog, the ANIMALNUMBER should be 1, for every Cat, the ANIMALNUMBER should be 2.

你把事情搞得太复杂了。最简单的解决方案是删除构造函数参数并保留 ANIMALNUMBER 不变。

但是

为子类定义 ID 意味着您稍后计划根据动物的 ANIMALNUMBER 执行一些特殊操作。

当我们进行 OOP 时，这不是我们想要的。

您以后想要基于ANIMALNUMBER做的事情应该在具体的“Animal”实现中的方法中完成(例如Dog)，覆盖类中的抽象方法动物

 public abstract class Animal {
  // common fields
   public Animal (int weight, int height) {
    // initialize
   }

   public abstract sting giveSound();
}

public class Dog extends Animal {
   @Override
   public  sting giveSound(){
     return "Wooff";
}


public class Cat extends Animal {
   @Override
   public  sting giveSound(){
     return "Meaw";
}

public class Rabbit extends Animal {
   @Override
   public  sting giveSound(){
     return "";
}

<小时/>

[编辑]

I will place these animals in a grid at some point. And I would like to count the number of Dogs, Cats and Rabbits I have.

我必须承认这是某种极端情况......

Can i count them based on their class?

是的，通过使用 map :

 public abstract class Animal {
   public addToCount(Map<String,Integer> counters){
     // gets the class name of the child that has been called *new* on...
     String myClassName =  getClass().getName(); 
     Integer oldCount = conters.getOrDefault(myClassName, Integer.ZERO);
     conters.put(myClassName,oldCount.add(Integer.ONE));
   }
}