> If Button is a like a Java interface (i.e. no behavior), then you don't
> need one in Ruby.  Just implement BigButton and LittleButton with
> compatible methods.

Well I'm trying to get rid of my way of thinking in Java and C++. I have modeled
a class that has objects of LittleButton and BigButton.
In Java I'd have:

class Window {
  private Button little = new LittleButton();
  private Button big = new BigButton();
}

I know that in Ruby I won't declare attributes like that but it's hard to me
to have a code that dosen't seems to my model.

What do you mean with compatible methods?