How to define an interface method to accept a class or any of its subclasses in Java?

Question

Suppose I have a class called Animal and an interface called AnimalTrainer.

public interface AnimalTrainer
 {
    void trainAnimal(Animal animal);
 }

Now, the problem arises when I want to write an implementation that trains only Lion, for example, where Lion extends Animal.

public class LionTrainer implements AnimalTrainer
 {
    public void trainAnimal(Lion lion)
      {
         // code 
      }
 }

But this doesn't work. How can I define the trainAnimal method in AnimalTrainer such that the above LionTrainer implementation is possible? Or would I have to change the LionTrainer implementation?

Answer 1

You need to type AnimalTrainer

public interface AnimalTrainer<T extends Animal>
 {
    public void trainAnimal(T animal);
 }

public class LionTrainer implements AnimalTrainer<Lion>
 {
    public void trainAnimal(Lion lion);
 }

Answer 2

Use generics:

public interface AnimalTrainer<T extends Animal> {
   void trainAnimal(T animal);
}
class LionTrainer implements AnimalTrainer<Lion> {
   public void trainAnimal(Lion lion) {...}
}

Answer 3

You should use generic types...

public interface AnimalTrainer<T extends Animal>
 {
    public void trainAnimal(T animal);
 }

then LionTrainer implements AnimalTrainer<Lion> ...