Question

I am trying to learn Subtyping in Java and I am not an better person in generics so I am getting this issue or doubt-

import java.util.ArrayList;
import java.util.Collection;

interface Animal<T>{}
class Lion implements Animal<Lion>{}
class Butterfly implements Animal<Butterfly>{}
class Cage<T>{
    public <T> void addAnimal(T t){

    }
}

interface CageAnimal<E> extends  Collection<E>{}
public class SubType<T> {

    public <T> SubType() {
        Lion lion = new Lion();
        Butterfly butterfly = new Butterfly();      
        /**
         * **Here inside Lion cage, we added Butterfly : WRONG**
         */
        Cage<Lion> cageLion = new Cage<Lion>();
        cageLion.addAnimal(lion);
        cageLion.addAnimal(butterfly);


        CageAnimal<Lion> cageAnimalLion = (CageAnimal<Lion>) new ArrayList<Lion>();
        cageAnimalLion.add(lion);

        //cageAnimalLion.add(butterfly);//Butterfly is Not Supposed to add here as it is the cage of Lion
    }   
}

In the above example when I declare Cage , why I am able to add Butterfly and in the Same case when I made CageAnimal type, I am not able to add any Buttefly

Cage<Lion> cageLion = new Cage<Lion>();
cageLion.addAnimal(lion);
cageLion.addAnimal(butterfly);

and in case of Cage

Cage<Animal> cageAnimalLion = new Cage<Lion>();
cageAnimalLion.addAnimal(lion);
cageAnimalLion.addAnimal(butterfly); //Throwing Compile Error

Answer 1

This line

 public <T> void addAnimal(T t){

should probably be

 public void addAnimal(T t){