Working of Constructors in vb.net

Constructors:

It is used to initialize the members of the class

VB.Net supports two types of constructors

• Instance constructors
• Shared constructors

Instance Constructors:

It is used to initialize the instance and the shared members of the class 

Syntax:

[Modifier] sub new ([arg info])                                                                                                  statement(s)                                                                                                                                    - - - - - - -                                                                                                                                                - - - - - - -                                                                                                                                            End sub

Note:

• Instance constructors will be invoked every time a new object is created for the class.
• A class can have any number of instance constructors.
• If a class is defined with more than one constructor then it is said to be the classes overloaded with constructors.
• If a constructor is defined using arguments then it is said to be parameterized constructor
• If a constructor is defined without any arguments then it is said to zero argument constructor.

Shared Constructors:

It is used to initialize the shared members of the class.

Syntax:

Shared sub new ( )                                                                                                 statement(s)                                                                                                                                    - - - - - - -                                                                                                                                            - - - - - - -                                                                                                                                            End sub

Observation:

• Shared constructors will be invoked only once whenever the class definition is loaded.
• A class can have maximum of only one shared constructors.
• Shared constructors can’t accept any arguments.

Project [menu] à Add new item à Module

Name: Constructors ‘‘Demo

‘‘‘Demo on constructors . . . . .

Imports system

Module constructors ‘‘Demo

Class Test

Public i as integer

Public shared s as integer

Sub new( ) ‘Instance constructor’

P = 100

S = 1000

End sub

Shared sub new( ) ‘Shared constructor’

S = 500

P = 500 error

End sub

End class

Sub main ( )

Console.WriteLine (“value of s before object creation: {0}”, Test.s)

Dim t As new Test

Console.WriteLine (“Value of t and s” after object creation: {0}, {1}”,                           t.p, Test.s)

                        End sub

End module

Observation:

• Whenever the value for the shared members has to be initialized before creating an object or if a constant value has to be assigned for the shared member then shared constructors should be used to initialize the shared members.
• Whenever the value for the shared member has to be reinitialized with a new value for every new instance created for a class then instance constructor should be used to initialize the shared members.