Let's say I have a main class A and another class B.
In the B class the user can change some settings and variables of the program that belongs to A, I want to be able to apply these changes to the A class, should I use inheritance and apply the changes to the father of B which is A or should I use composition and pass the instance of A to class B and change the variables of A in this manner?
which one is best practice and why?
note : If it helps in anyway, I'm writing a gui application and A is my main window and B is a setting window opened from A.

  • 1
    If instances of A can be replaced by B, then you can use the decorator pattern via inheritance. Otherwise I would tend towards composition.
    – lealand
    Commented Apr 3, 2015 at 20:19
  • This SE thread may be helpful
    – radarbob
    Commented Apr 7, 2015 at 1:07

1 Answer 1


Inheritance is "is-a", composition is "has-a". Is it the case that "a B is-an A", or it is the case the "a B has-an A for some reason"?

It is obvious that setting window is-not-a main window, but is an external actor. So it should have an A passed in.

EDIT: Since you told what A and B is, that is, windows, you should separate domain from presentation; that is, not even B should be passed an A (no, those are just views), but B's model should be passed A's model. But treat this just as an additional note, as original question was about inheritance vs. composition.

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