Question

Possible Duplicate:
Regarding factory design pattern through reflection

I was doing R&D on factory pattern I have developed the below code. Right now I know the subclasses are Dog and Cat, but please advise me. What to do if I want to achieve the same thing through reflection by passing the class name in main.java?

Animal

public abstract class Animal {
    public abstract String makeSound();
}

Dog

public class Dog extends Animal {

    @Override
    public String makeSound() {
        return "Woof";
    }
}

Cat

public class Cat extends Animal {

    @Override
    public String makeSound() {
        return "Meow";
    }
}

AnimalFactory

public class AnimalFactory {

    public Animal getAnimal(String type) {
        if ("canine".equals(type)) {
            return new Dog();
        } else {
            return new Cat();
        }
    }
}

Main

public class Main {

    public static void main(String[] args) {
        AnimalFactory animalFactory = new AnimalFactory();

        Animal a1 = animalFactory.getAnimal("feline");
        System.out.println("a1 sound: " + a1.makeSound());

        Animal a2 = animalFactory.getAnimal("canine");
        System.out.println("a2 sound: " + a2.makeSound());
    }
}

Please advise it how I can add reflection functionality into it so that I don’t need to even determine the type, just pass the class name in the main java and object of that subclass gets created.

Answer 1

If you pass the fullyqualified name of the class, you can instantiate them as following:

return (Animal) Class.forName(fullyQualifiedClassName).newInstance();

To avoid ClassCastException, you could test that the returned class of Class.forName() is indeed a subclass of Animal before invoking newInstance(). Use isAssignableFrom for that.