Java泛型类型: how to pass the right class type properly?

Question

我有一个像这样的抽象类:

public abstract class AnimalService<T extends Animal> {
   ...
   public T callAPI() {
     // here the Class<T> can be Fish.class or Salmon.class or any child class type of Animal
     return restTemplate.getForObject(url, Class<T>, params); 
   }
}

和一个子类:

public class FishService<T extends Fish> extends AnimalService<Fish> {
   ...
}

和一个孙子类:

public class SalmonService extends FishAnimalService<Salmon> {
   ...
}

我认为这个传承存在设计问题。但是，当我调用 callAPI() (在 FishService 或 SalmonService 中)时，我怎样才能实现这一点，我能够传递准确的 类类型(例如Fish.class或Salmon.class)，我在其中调用？

Answer 1

一种选择是添加一个在子类中重写的抽象方法以返回正确的类类型:

public abstract class AnimalService<T extends Animal> {
   public T callAPI() {
     return restTemplate.getForObject(url, getAnimalClass(), params); 
   }
   abstract Class<T> getAnimalClass();
}

public class SalmonService extends FishAnimalService<Salmon> {
   Class<Salmon> getAnimalClass() {
      return Salmon.class;
   }
}

另一种选择是引入实例变量。

abstract class AnimalService<T extends Animal> {
   private Class<T> animalClass;

   protected AnimalService(Class<T> animalClass) {
      this.animalClass = animalClass;
   }

   public T callAPI() {
     return restTemplate.getForObject(url, animalClass, params); 
   }
}

public class FishService<T extends Fish> extends AnimalService<Fish> {
   protected FishService(Class<T> fishClass) {
      super(fishClass);
   }
}


public class SalmonService extends FishAnimalService<Salmon> {
   public SalmonService() {
      super(Salmon.class);
   }
}