Question

Maybe the title is not so clear. Let me clarify what I’m trying to accomplish.

I have to base classes:

• BaseProperties
• BaseProblem

BaseProperties contains data about the generation of math problems. For example, in the image above, BasicAdditionProperties contains Addend1 and Addend2, this two objects know about the range of the generated value to represent a BasicAdditionProblem.

So, this is just an idea.. I guess I supposed to pass the abstract class to a factory, and this one should generate the problem (in this case BasicAdditionProblem).

I have read, it’s recomended pass these values as the base class. And my main doubt is, when I pass the object BaseProperties to the factory, all the time do I have to cast the object?

Or what ideas can I implement to model this scenario? Or do I have to have a static Factory where maintain and be used as mapping to the concrete factories?
Thanks in advance.

Answer 1

Define an abstract CreateProblem() in the BaseProperties class. This method can be used generically to allow each concrete Properties subclass to provide its own Factory method.

This is similar to using an instance of WebRequest subclass and calling GetResponse() on it and it then returns the coresponding subclass of WebResponse.

This distributed abstract factory approach allows you to add property/problem pairs easily to the system because the code to map the two is solely contained in those two classes.

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You could also use a full Abstract Factory implementation where you have PropertyProblemFactory that defines a CreateProperties() and a CreateProblem(). So in your example you would have AdditionFactory that knows how to create the matching set. But this forces you to define an additional class for each Property/Problem pair. It also works best when you have a class that uses the current/selected PropertyProblemFactory, creates a Properties with it, and then immediately uses that same PropertyProblemFactory factory to create the matching Problem. Once you let go of the reference to the factory and solely have just a reference to the Properties, it is harder to re-locate the right factory to create the Problem. (This can be addressed with yet another class to map object types to factories, but the complexity rises. So the first appoach I suggested is better in this kind of situation).