在 Java 的子类中专门化方法参数

2022-01-24 00:00:00 inheritance design-patterns polymorphism java

考虑以下情况:

public abstract class AnimalFeed{
}
public class FishFeed extends AnimalFeed{
}
public class BirdFeed extends AnimalFeed{
}

public abstract class Animal{

public void eat(AnimalFeed somethingToEat)

}

现在我想定义一个扩展动物"的鸟"类，确保当鸟吃东西时，它只吃鸟食.

Now I would like to define a class "Bird" extending "Animal" being sure that when the bird eats, it eats only BirdFeed.

一种解决方案是指定一种合约，其中吃"的调用者必须传递适当提要的实例

One solution would be to specify a sort of contract, in which the caller of "eat" must pass an instance of the appropriate feed

public class Bird extends Animal{

@Override 
public void eat(AnimalFeed somethingToEat){

    BirdFeed somethingGoodForABird

    if(somethingToEat.instanceOf(BirdFeed)){
    somethingGoodForABird = (BirdFeed) somethingGoodForABird
    }else{
    //throws error, complaining the caller didn't feed the bird properly
    }
}
}

将参数的责任委托给调用者是否可以接受?如何强制调用者传递参数的特化?是否有替代设计解决方案?

Is it acceptable to delegate the responsibility of the parameter to the caller? How to force the caller to pass a specialization of the parameter? Are there alternative design solutions?

推荐答案

你需要在类中添加一个类型变量:

You'd need to add a type variable to the class:

public abstract class Animal<F extends AnimalFeed> {
  public abstract void eat(F somethingToEat);
}

然后您可以将您的子类声明为需要特定类型的 AnimalFeed:

Then you can declare your subclasses as wanting a particular type of AnimalFeed:

public class Bird extends Animal<BirdFeed> {
  public void eat(BirdFeed somethingToEat) {}
}

public class Fish extends Animal<FishFeed> {
  public void eat(FishFeed somethingToEat) {}
}

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