Object-Oriented Programming Concepts

This is the first in a series of articles describing the use of object-oriented programming techniques as implemented by the C# programming language. This series follows the C# Fundamentals tutorial that beginners are advised to read first.

Tutorial Prerequisites

The .NET Framework includes all of the software required to compile a program that can be developed using any standard text editor. However, Microsoft provides many development environments that are suitable and make programming and debugging much easier.

Microsoft Visual Studio is an ideal development environment for this tutorial if you have it available. If not, I strongly suggest downloading Microsoft's excellent, and free-of-charge, development environment, Microsoft C# Express Edition. However, if you have another preferred development environment for C# programming, you should easily be able to adapt the examples accordingly.

What is Object-Oriented Programming?

As computers increase in processing power, the software they execute becomes more complex. This increased complexity comes at a cost of large programs with huge codebases that can quickly become difficult to understand, maintain and keep bug-free.

Object-oriented programming (OOP) tries to alleviate this problem by creating networks of objects, each like a small software 'machine'. These objects are naturally smaller entities, simplifying the development task of each unit. However, when the objects co-operate in a system, they become the building blocks of much more complex solution.

Consider the motor car. If a car were designed as a single machine, it would be seen as hugely complex with lots of opportunities for failure. However, when broken down into its constituent parts, such as wheels, pedals, doors, etc. the individual design items become simpler. Each part (or object) is created independently, tested carefully and then assembled into the final product. The creation of the parts can be simplified further when they are broken down into even simpler items. For example, when each door is considered as being composed of an outer panel, handle, inner panel and window.

The car example is analogous to the object-oriented software. Rather than writing a huge program to create, for example, a project management system, the solution is broken into real-world parts such as project, task, estimate, actual, deliverable, etc. Each of these can then be developed and tested independently before being combined.

Key Concepts

This tutorial describes the use of object-oriented techniques with the C# programming language. Before we start to examine any sample code, it is important to review the ideas that will be discussed. Some of the key concepts are described in the following sections.

Classes and Objects

The basic building blocks of object-oriented programming are the class and the object. A class defines the available characteristics and behaviour of a set of similar objects and is defined by a programmer in code. A class is an abstract definition that is made concrete at run-time when objects based upon the class are instantiated and take on the class' behaviour.

As an analogy, let's consider the concept of a 'vehicle' class. The class developed by a programmer would include methods such as Steer(), Accelerate() and Brake(). The class would also include properties such as Colour, NumberOfDoors, TopSpeed and NumberOfWheels. The class is an abstract design that becomes real when objects such as Car, RacingCar, Tank and Tricycle are created, each with its own version of the class' methods and properties.

Car	Racing Car	Tank	Tricycle
Colour: Red NumberOfDoors: 2 NumberOfWheels: 4 TopSpeed: 60mph	Colour: Yellow NumberOfDoors: 0 NumberOfWheels: 4 TopSpeed: 200mph	Colour: Green NumberOfDoors: 1 NumberOfWheels: 12 TopSpeed: 40mph	Colour: Orange NumberOfDoors: 0 NumberOfWheels: 3 TopSpeed: 50mph