Appendix A: Principles of Object- Oriented Programming

Overview

In general, when learning a new programming language, you will spend a fair part of your effort learning the syntax of that language: how to declare variables, how to control the flow of execution, and so on. However, to write quality code, you also need to understand the principles and methodologies behind the language. C# is a fully object-oriented language, so in order to create well-designed C# code you need to come to grips with its object-oriented features, and that means learning about object-oriented programming (OOP).

In OOP, you aim to write easily maintainable and reusable pieces of code that can perform collectively very complex tasks. However, the whole structure of an object-oriented program is very different from the structure of an equivalent program written in a procedural language. This appendix introduces the principles of object-oriented programming. Although you'll see some C# syntax (because the examples are presented in C#) throughout this appendix, the emphasis is on learning those principles that apply to OOP in general, no matter which language you are using.

OOP is an extremely powerful methodology. Once you've familiarized yourself with writing your code using OOP, you will probably wonder how you ever got by without it. You'll find that, unlike procedural languages, OOP gives your code an intuitive, "natural" structure. Even Visual Basic 6, which implements a few object-oriented features, cannot keep up with true OOP.

The appendix starts by discussing the nature of an object before moving on to examine the concept of inheritance. Inheritance, which is at the heart of OOP, enables you to conveniently reuse the code for classes. You'll learn how to use inheritance in your programs both from a conceptual and C# point of view.