VB.NET Classes


  • A class is a user-defined data type.
  • It is the base of object-oriented programming language.
  • A class contains variable and methods inside its body.

Defining a Class


Class is defined using the keyword class. The syntax for defining a class in VB.NET is as follows:


Syntax

Class class-name
Variable-declaration
Method-declaration
End Class

Adding Variables to a Class


  • Data is encapsulated in a class by putting data fields inside the body of a class.
  • The syntax for declaring variables in class is as follows:
  • Class class-name
    Access-modifier data-type variable1
    Access-modifier data-type variable2
    …………………………….
    …………………………….
    End Class

  • You can declare any number of variables in a class.

Adding Methods to a Class


  • Methods are used to perform the operations on the variables. A method may or may not return a value.
  • A method which returns a value is called a function.
  • A method that does not return any value is called a sub-procedure.
  • The syntax for declaring a Function is as follows:
[access-modifier] Function function-name(parameter-list) As type
Function-body
End Function

In the above syntax access-modifier are used to define the scope of the function inside the program. We will study about the access-modifier in next chapter. Parameter-list is representing the list of parameter the Function accepts. Type is representing the data-type of value returned by the Function.


The syntax for declaring a sub-procedure is as follows:


[access-modifier] Sub sub procedure-name(parameter-list) As type
Sub procedure-body
End Sub

Here is an example of definition of class having variables and methods defined inside its body:


Class addition
Private a As Integer=2
Private b As Integer=3
Private c As Integer
Public Sub add()
c=a+b
………….
End Sub
End Class

VB.NET Objects


  • Object is instance of class which can access all the members of class.
  • A class is an abstract concept means it is not exist in really but object is a realistic concept which contains all properties of the class. For example if vegetable is a class then potato, leady-finger, bringle etc are its object.
  • The actual instance of class is created by making its objects.
  • All objects of the class have their own copies of variables and method defined in the class.
  • The syntax for declaring an object in VB.NET 2010 is as follows:
  • Dim object-name As New class-name()

After creating an object of class we can access the member of class through the object. The syntax for accessing the members of class through the object is as follows:


Object-name.Variable-name
Object-name.method-name()

Here is an example of VB.NET Classes and Object:


Module Module1
Class addition 'class definition
'declaring variable in class
Private a As Integer = 2
Private b As Integer = 3
Private c As Integer
'declaring sub-procedure in class
Public Sub add(ByVal a As Integer, ByVal b As Integer)
c = a + b
Console.WriteLine("Addition is=" & c)
End Sub
End Class
Sub Main()
Dim obj1 As New addition() 'creating object of class
obj1.add(4, 5) 'access member method using object
Console.ReadLine()
End Sub
End Module

The output of the above program is given below:


Addition is=9