A Summary of Object-Oriented Principles

In the course of the discussion on design patterns, I have stated a number of the principles of the object-oriented paradigm. These principles can be summarized as follows:

• Objects are things with well-defined responsibilities.

• Objects are responsible for themselves.

• Encapsulation means any kind of hiding

  - Data-hiding

  - Class hiding (behind an abstract class or interface)

  - Implementation hiding

• Abstract out variations in behavior and data with commonality/variability analysis.

• Design to interfaces.

• Think of inheritance as a method of conceptualizing variation, not for making special cases of existing objects.

• Keep variations in a class decoupled from other variations in the class.

• Strive for loose coupling.

• Strive for high cohesion.

• Be absolutely meticulous in applying the once and only once rule.