1. Stéphane Ducasse 1
Stéphane Ducasse
stephane.ducasse@inria.fr
http://stephane.ducasse.free.fr/
Design Points - Dual
Interfaces
Stéphane Ducasse --- 2005

2. S.Ducasse 2
Clients?
• Clients
• Subclasses

3. S.Ducasse 3
What are the consequences?
A
{ private x ;
void foo(){ ... x ...}
}

4. S.Ducasse 4
What can I do as a subclass?
I cannot access x
I cannot replace x
I cannot extend!

5. S.Ducasse 5
The idiom is
Fields are private AND you provide protected
accessors
OR
Fields are protected

6. S.Ducasse 6
Benefits
Your clients cannot access your fields
But your subclasses are empowered

7. S.Ducasse 7
Two users

8. S.Ducasse 8
Two Users

9. S.Ducasse 9
Clients
A class has always two clients:
its clients and its extenders

10. S.Ducasse 9
Clients
A class has always two clients:
its clients and its extenders