Build Your Own ASP.NET 2.0 Web Site Using C# & VB, Second Edition

mentals of OOP and learn how adopting good OOP style now can help you to

develop better, more versatile web applications down the road. This section will

provide a basic OOP foundation angled towards the web developer. In particular,

we’ll cover the following concepts:

❑

objects

❑

properties

❑

methods

❑

classes

❑

scope

❑

events

❑

inheritance

In the pages that follow, we’ll discuss these concepts briefly, and from Chapter 4

onwards, you’ll see some practical examples of OOP in action.

Objects and Classes

So what does the term “object oriented programming” mean? Basically, as the

name suggests, it’s an approach to development that puts objects at the center

of the programming model. The object is probably the most important concept

in the world of OOP; an object is a self-contained entity that has state and beha-

vior, just like a real-world object.

In programming, an object's state is described by its fields and properties, while

its behavior is defined by its methods and events. An important part of OOP’s

strength comes from the natural way it allows programmers to conceive and

design their applications.

We often use objects in our programs to describe real-world objects—we can have

objects that represent a car, a customer, a document, or a person. Each object

has its own state and behavior.

It’s very important to have a clear understanding of the difference between a

class and an object. A class acts like a blueprint for the object, while an object

represents an instance of the class. I just said that you could have objects of type

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Objects and Classes

Car, for example. If you did, Car would be the class, or the type, and we could

create as many Car objects as we wanted, calling them myCar, johnsCar, davesCar,

and so on.

The class defines the behavior of all objects of that type. So all objects of type

Car will have the same behavior—for example, the ability to change gear. However,

each individual Car object may be in a different gear at any particular time; thus,

each object has its own particular state.

Let’s take another example: think of Integer (or int) as a class, and age and

height as objects of type Integer. The class defines the behavior of the ob-

jects—they’re numeric, and we can perform mathematical operations on

them—and the instances of objects (age and height) have their behavior defined

by the class to which they belong, but they also hold state (so age could be 20).

Take a look at the following code:

Visual Basic

Dim age As Integer

Dim name As String

Dim myCar as Car

Dim myOtherCar as Car

C#

int age;

string name;

Car myCar;

Car myOtherCar;

As you can see, the syntax for declaring an object is the same as that for declaring

a simple integer or string variable. In C#, we first mention the type of the object,

then we name that particular instance. In VB, we use the Dim keyword.

Object oriented programming sounds like an advanced topic, but getting started

with it is actually very easy, because OOP offers us a natural way to conceive and

design programs. Instead of writing long functions of code to perform specific

tasks, OOP allows us to group pieces of related functionality into classes that we

can reuse over and over, or even extend to incorporate new features. In OOP,

one thinks of programming problems in terms of objects, properties, and methods.

And, as we’ve seen, the best way to get a handle on these terms is to consider a

real-world object and imagine how it might be represented in an OOP program.

For the examples that follow, we’ll use as our example my dog, an Australian

Shepherd named Rayne.

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Chapter 3: VB and C# Programming Basics