Producing a generic correctly

Hi,

I've been having trouble with using generics the right way. I put together a complete example of what I wanted to do, which is below. My problem is that I kept trying to figure out a way for a generic class to produce an instance of the generic type 'internally', which just doesn't want to work without a cast and even that will produce a warning (though it does work). Here is my favorite barn example:



// Barn.java
import java.util.ArrayList;

public class Barn<TAnimal extends Animal>
{
    protected ArrayList<TAnimal> m_animals = new ArrayList<TAnimal>();
      
    protected FactoryAnimal m_factory;
   
    public Barn()
    {
    }
   
    public void addAnimal(TAnimal animal)
    {
          m_animals.add(animal);
    }
   
    public void setFactory(FactoryAnimal factory)
    {
          m_factory = factory;
    }
   
    public void magic()
    {
          // This won't work even though we know we were
          // initialized with a Horse type and that the factory
        // is actually producing a Horse instance.
          m_animals.add(m_factory.createAnimal());
    }
}


// Animal.java
public class Animal
{
      public Animal(){}
}


// Horse.java
public class Horse extends Animal
{
      public Horse(){}
}


// FactoryAnimal.java
public abstract class FactoryAnimal
{
      public abstract Animal createAnimal();
}


// FactoryHorse.java
public class FactoryHorse extends FactoryAnimal
{
      public FactoryHorse() {}
      
      public Animal createAnimal()
      {
            return new Horse();
      }
}


// Main driver class.
public class TestGenerics
{
      public static void main(String[] args)
      {
            Barn<Horse> barn = new Barn<Horse>();
            barn.setFactory(new FactoryHorse());
            
            // This won't work.
            barn.magic();
            
            // This is ok because 'outside' we know Barn
            // has been initialized with type Horse.
            barn.addAnimal(new Horse());
      }
}



Yeah so what I can do is use a cast like:

    m_animals.add((TAnimal)m_factory.createAnimal());

inside the Barn class but it will produce a warning and just doesn't look good.

Sorry if it seems like I keep going in circles with this stuff, I was hoping to make this little library as easy to use as possible, and believe my salvation lies within generics!

Thanks