Object Oriented Design

• UML Cheatsheet
• Program to an interface, not an implementation.
• Always remove code duplication.
• Favour object composition (wrappers) over class inheritance.
• Always use most restrictive options by default, i.e sealed, non-virtual, private - only open up if maintenance/backwards compatibility ramifications are accepted.
• Know where to use:
  • Aspect Oriented Programming (example) for cross cutting concerns.
  • Dependency Injection (DI) / Inversion of Control (IoC) architecture (framework list) for testability and pluggable provider patterns.
    • Typically done by sending an interface type to a constructor.
  • Unit testing frameworks such as NUnit.
  • Mock frameworks (such as Moq) to use with unit testing to mock (fake) an object the method you are testing calls (relies on DI object design)
  • Use Design patterns.
  • Consider use of the MS Enterprise Library:
    • Caching Application Block.
    • Cryptography Application Block.
    • Data Access Application Block.
    • Exception Handling Application Block.
    • Logging Application Block.
    • Policy Injection Application Block.
    • Security Application Block.
    • Unity Application Block.
    • Validation Application Block.

Design Principles

Low Coupling

Given two lines of code, A and B, they are coupled when B must change behavior only because A changed.

High Cohesion

• They are cohesive when a change to A allows B to change so that both add new value.
• Cohesion is inversely proportional to the number of responsibilities (methods) a module (class) has.

Separation of Concerns

Low coupling and high cohesion can be achieved through separation of concerns, modularity and information hiding / encapsulation.

• Well defined stable public interfaces with private implementation details.