Question

I am trying to see if there is a design pattern that can solve this:

I have created an abstract class A with properties a,b and c. I have another class B that extends the class A and adds more properties: x,y,z. Then I have another class C that again extends A and adds i,j,k. Lastly I have a factory method that determines which instance to create B or C and thats the part where I need help. How or what should this factory method return: If it returns an instance of A than I wouldnt know which specific instance was created B or C? I need this factory method to create a concrete instance. Now, I know that I could write static method like createB or createC but I am looking for a more general solution maybe another design pattern here.

Update: The reason I want to know the concrete class is that I need to pass this object to a frontend jsp. That JSP would need to know what specific class was instantiated so it can call the appropriate getters.

Answer 1

I would Keep Factory Pattern as it should. so the return type would be the Abstract A class. B & C Should also inherit their properties through Proxy Pattern.

So Make CAble & BAble Interfaces and use C & B as instances of A (as they’re both generated by the same factory), then cast B & C to act as their Interfaces Describe.

Cheers!

UPDATE:

I think I’ve figured what you need, picture the following:
In a School Page.
There is a general view of Students & Professors, both have common and individual fields, but the common request is schoolMember.

class SchoolMember // The return type of your Factory
  -name
  +getView():SchoolMemberView // Will be used by the View//View Model

Interface Professor
  getProfession()
Interface Student
  getSemester() 

class FacultyMamber: SchoolMember,Professor
  -profession
  +getView():SchoolMemberView
class UniStudent: SchoolMember,Student
  -semmester
  +getView():SchoolMemberView