[英]Java generic type : how to pass the right class type properly?
我有一個像這樣的抽象類:
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);
}
}
和一個子類:
public class FishService<T extends Fish> extends AnimalService<Fish> {
...
}
和一個孫子類:
public class SalmonService extends FishAnimalService<Salmon> {
...
}
我認為這種遺產存在設計問題。 但是,當我調用callAPI()
(在FishService
或SalmonService
)時,我如何能夠傳遞我調用的確切類類型(例如Fish.class
或Salmon.class
)?
一種選擇是添加一個在子類中重寫的抽象方法以返回正確的類類型:
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;
}
}
另一種選擇是引入實例變量。
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);
}
}
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