I think the question is on Factory Method Pattern. So I 
will go in that direction. However there is another pattern 
called the Abstract Factory Pattern which is realted to 
Factory Method Pattern.

If we have to hide the "Creation" of an object and its 
Concrete type to a client, then the tendency is to 
use "Factory Method Pattern".

Normally a factory method is a method that is part of 
an "Abstract Factory". Client calls the factory method on 
an abstract factory which is a concrete object of an 
interface whose type may or may not be known to the client, 
to get a concrete object of the interface for product whose 
concrete type may or may not be useful to the client.