Covariant Types: C# vs Java

c#.cs

public abstract class Animal 
{
    public abstract string Name { get; }
}
public abstract class AnimalFactory
{
    public abstract Animal Create ();

    public abstract void Process (Animal animal);
}


public class Cat : Animal
{
    public override string Name { get { return "Cat"; } }
}
public class CatFactory : AnimalFactory
{
    // Can't return Cat, must be Animal
    public override Animal Create ()
    {
        return new Cat ();
    }

    // Can't pass in Cat, must be Animal
    public override void Process (Animal animal)
    {
    }
}

java.java

public abstract class Animal {
    public abstract String getName ();
}
public abstract class AnimalFactory {
    public abstract Animal create ();
    public abstract void process (Animal animal);
}

public class Cat extends Animal {
    @Override
    public String getName () {
        return "Cat";
    }
}

public class CatFactory extends AnimalFactory {
    // We can return Cat here instead of Animal
    @Override
    public Cat create () {
        return new Cat ();
    }

    // Still must pass in Animal here
    @Override
    public void process (Animal cat) {
        
    }
}