FIRST WE SEE ABOUT VB THEN ABOUT VB.NET
VB.NET IS USED TO CREATE WINDOW BASED APPLICATIONS
generally this type of applications cant run in other systems,but can be done through sharing...ok ,Then what is ASP.NET IT IS USED TO CREATE WEB BASED APPLICATIONS..ASP STANDS FOR ACTIVE SERVER PAGE..the web pages are nowadays created by asp.net.....to our knowledge asp and asp.net are different
asp.net is fully different from asp ..The advantage of asp.net is that secure coding ie code behind language and page back facility ...ok now we can see about vb
OOP 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.
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.
