Re: Integrating concurrent & O-O programming

[tma@osc.COM (Tim Atkins)]

In article <7062@hubcap.clemson.edu> wtwolfe@hubcap.clemson.edu (Bill Wolfe) writes:
> ...consider the interference that occurs between class inheritance 
> and encapsulation when subclasses are allowed to access freely the 
> instance variables of the parent class [Sny86].  In this case we may 
> say that support for inheritance diminishes the degree of encapsulation
> that was achieved without inheritance...


I have heard this before and, frankly, I don't get it.  The subclass 
has inherited data structure definition from the parent class.  Therefore
its instances will contain instances of the parent data structure.  This
is totally local to the object!  Only the definition was inherited.  Why
is this a bad thing?  Why does it break encapsulation?  I understood the
encapsulation wrt data provided by OO techniques to simply state that instance
data should not be accessed directly but only through a method defined on
the class.  Therefore, inheritance does not seem to break encapsulation.

I would appreciate it if someone could set me straight here.

- Tim