3 Object Oriented Design Principles

3.1 Write code that declares, implements and/or extends interfaces
3.2 Choose between interface inheritance and class inheritance
3.3 Apply cohesion, low-coupling, IS-A, and HAS-A principles
3.4 Apply object composition principles (including has-a relationships)
3.5 Design a class using a Singleton design pattern
3.6 Write code to implement the Data Access Object (DAO) pattern
3.7 Design and create objects using a factory pattern