Classes n Objects VB Language

Visual Basic .NET is Object-Oriented. Everything we do in Visual Basic involves objects in some way or other and everything is based on the Object class. Controls, Forms, Modules, etc are all types of classes. Visual Basic .NET comes with thousands of built-in classes which are ready to be used. Let's take a closer look at Object-Oriented Programming in Visual Basic. We will see how we can create classes, objects, how to inherit one class from other, what is polymorphism, how to implement interfaces and so on. We will work with Console Applications here as they are simple to code.

Classes and Objects

Classes are types and Objects are instances of the Class. Classes and Objects are very much related to each other. Without objects you can't use a class. In Visual Basic we create a class with the Class statement and end it with End Class. The Syntax for a Class looks as follows:

Public Class Test

----- Variables
-----Methods
-----Properties
-----Events

End Class


The above syntax created a class named Test. To create a object for this class we use the new keyword and that looks like this: Dim obj as new Test(). The following code shows how to create a Class and access the class with an Object. Open a Console Application and place the following code in it.

Module Module1
Imports System.Console

Sub Main()
Dim obj As New Test()
'creating a object obj for Test class
obj.disp()
'calling the disp method using obj
Read()
End Sub

End Module

Public Class Test
'creating a class named Test
Sub disp()
'a method named disp in the class
Write("Welcome to OOP")
End Sub
End Class


Output of above code is the image below.



Fields, Properties, Methods and Events

Fields, Properties, Methods, and Events are members of the class. They can be declared as Public, Private, Protected, Friend or Protected Friend.

Fields and Properties represent information that an object contains. Fields of a class are like variables and they can be read or set directly. For example, if you have an object named House, you can store the numbers of rooms in it in a field named Rooms. It looks like this:

Public Class House
Public Rooms as Integer
End Class


Properties are retrieved and set like fields but are implemented using Property Get and Property Set procedures which provide more control on how values are set or returned.

Methods represent the object’s built-in procedures. For example, a Class named Country may have methods named Area and Population. You define methods by adding procedures, Sub routines or functions to your class. For example, implementation of the Area and Population methods discussed above might look like this

Public Class Country
Public Sub Area()
Write("--------")
End Sub
Public Sub population()
Write("---------")
End Sub
End Class


Events allow objects to perform actions whenever a specific occurrence takes place. For example when we click a button a click event occurs and we can handle that event in an event handler.

OOPS with VB

OOPS with VB

OOPS Basics

Visual Basic was Object-Based, Visual Basic .NET is Object-Oriented, which means that it's a true Object-Oriented Programming Language. Visual Basic .NET supports all the key OOP features like Polymorphism, Inheritance, Abstraction and Encapsulation. It's worth having a brief overview of OOP before starting OOP with VB.

Why Object Oriented approach?

A major factor in the invention of Object-Oriented approach is to remove some of the flaws encountered with the procedural approach. In OOP, data is treated as a critical element and does not allow it to flow freely. It bounds data closely to the functions that operate on it and protects it from accidental modification from outside functions. OOP allows decomposition of a problem into a number of entities called objects and then builds data and functions around these objects. A major advantage of OOP is code reusability.

Some important features of Object Oriented programming are as follows:



Emphasis on data rather than procedure

Programs are divided into Objects

Data is hidden and cannot be accessed by external functions

Objects can communicate with each other through functions

New data and functions can be easily added whenever necessary

Follows bottom-up approach

Concepts of OOP:


Objects

Classes

Data Abstraction and Encapsulation

Inheritance

Polymorphism

Briefly on Concepts:

Objects

Objects are the basic run-time entities in an object-oriented system. Programming problem is analyzed in terms of objects and nature of communication between them. When a program is executed, objects interact with each other by sending messages. Different objects can also interact with each other without knowing the details of their data or code.

Classes

A class is a collection of objects of similar type. Once a class is defined, any number of objects can be created which belong to that class.

Data Abstraction and Encapsulation

Abstraction refers to the act of representing essential features without including the background details or explanations. Classes use the concept of abstraction and are defined as a list of abstract attributes.

Storing data and functions in a single unit (class) is encapsulation. Data cannot be accessible to the outside world and only those functions which are stored in the class can access it.

Inheritance

Inheritance is the process by which objects can acquire the properties of objects of other class. In OOP, inheritance provides reusability, like, adding additional features to an existing class without modifying it. This is achieved by deriving a new class from the existing one. The new class will have combined features of both the classes.

Polymorphism

Polymorphism means the ability to take more than one form. An operation may exhibit different behaviors in different instances. The behavior depends on the data types used in the operation. Polymorphism is extensively used in implementing Inheritance.

Advantages of OOP

Object-Oriented Programming has the following advantages over conventional approaches:


OOP provides a clear modular structure for programs which makes it good for defining abstract datatypes where implementation details are hidden and the unit has a clearly defined interface.

OOP makes it easy to maintain and modify existing code as new objects can be created with small differences to existing ones.

OOP provides a good framework for code libraries where supplied software components can be easily adapted and modified by the programmer. This is particularly useful for developing graphical user interfaces.


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