In visual basic, Constructor is a method and it will invoke automatically whenever an instance of class or struct is created. The constructor is useful to initialize and set default values for the data members of the new object.
In case, if we create a class without having any constructor, the compiler will automatically create a one default constructor for that class. So, there is always one constructor that will exist in every class.
In visual basic, a class can contain more than one constructor with a different type of arguments and the constructors will never return anything, so we don’t need to use any return type, not even void while defining the constructor method in the class.
As discussed, the constructor is a method and it won’t contain any return type. If we want to create a constructor in visual basic, we need to create a method with New keyword.
Following is the syntax of creating a constructor in visual basic programming language.
Public Class User
' Constructor
Public Sub New()
' Your Custom Code
End Sub
End Class
If you observe the above syntax, we created a class called “User” and a method with New keyword. Here the method New() will become a constructor of our class.
In visual basic, we have a different type of constructors available, those are
Now, we will learn about each constructor in detail with examples in a visual basic programming language.
In visual basic, if we create a constructor without having any parameters, we will call it as default constructor and the instance of the class will be initialized without any parameter values.
Following is the example of defining the default constructor in visual basic programming language.
Module Module1
Class User
Public name, location As String
' Default Constructor
Public Sub New()
name = "Suresh Dasari"
location = "Hyderabad"
End Sub
End Class
Sub Main()
' The constructor will be called automatically once the instance of the class created
Dim user As User = New User()
Console.WriteLine(user.name)
Console.WriteLine(user.location)
Console.WriteLine("Press Enter Key to Exit..")
Console.ReadLine()
End Sub
End Module
If you observe the above example, we created a class called “User” and the constructor method “New()” without having any parameters. When we create an instance of our class (User), then automatically our constructor method will be called.
When we execute the above visual basic program, we will get the result as shown below.
If you observe the above result, our constructor method has called automatically and initialized the parameter values after creating an instance of our class.
In visual basic, if we create a constructor with at least one parameter, we will call it a parameterized constructor and every time the instance of the class must be initialized with parameter values.
Following is the example of defining the parameterized constructor in a visual basic programming language.
Module Module1
Class User
Public name, location As String
' Parameterized Constructor
Public Sub New(ByVal a As String, ByVal b As String)
name = a
location = b
End Sub
End Class
Sub Main()
' The constructor will be called automatically once the instance of the class created
Dim user As User = New User("Suresh Dasari", "Hyderabad")
Console.WriteLine(user.name)
Console.WriteLine(user.location)
Console.WriteLine("Press Enter Key to Exit..")
Console.ReadLine()
End Sub
End Module
If you observe the above example, we created a class called “User” and the constructor method “New(string, string)” with parameters. When we create an instance of our class (User) with required parameters, then automatically our constructor method will be called.
When we execute the above visual basic program, we will get the result as shown below.
If you observe the above result, our constructor method has called automatically and initialized the parameter values after creating an instance of our class with the required parameters.
In the next chapters, we will learn about copy constructor and private constructor in a visual basic programming language with examples.
In visual basic, we can overload the constructor by creating another constructor with the same method name but with different parameters.
Following is the example of implementing a constructor overloading in a visual basic programming language.
Module Module1
Class User
Public name, location As String
' Default Constructor
Public Sub New()
name = "Suresh Dasari"
location = "Hyderabad"
End Sub
' Parameterized Constructor
Public Sub New(ByVal a As String, ByVal b As String)
name = a
location = b
End Sub
End Class
Sub Main()
' Default Constructor will be called
Dim user As User = New User()
' Parameterized Constructor will be called
Dim user1 As User = New User("Rohini Alavala", "Guntur")
Console.WriteLine(user.name & ", " & user.location)
Console.WriteLine(user1.name & ", " & user1.location)
Console.WriteLine(vbLf & "Press Enter Key to Exit..")
Console.ReadLine()
End Sub
End Module
If you observe the above example, we created a class called “User” and overloaded the constructor “New()” by creating another constructor “New(string, string)” with same name but with different parameters.
When we execute the above visual basic program, we will get the result as shown below.
If you observe the above result, the respective constructor methods have been called automatically when we created an instance of our class with or without parameters based on our requirements.
In visual basic, Constructor Chaining is an approach to invoke one constructor from another constructor. To achieve constructor chaining we need to use Me keyword after our constructor definition.
Following is the example of implementing a constructor chaining in a visual basic programming language.
Module Module1
Class User
Public Sub New()
Console.Write("Hi, ")
End Sub
Public Sub New(ByVal a As String)
Me.New()
Console.Write(a)
End Sub
Public Sub New(ByVal a As String, ByVal b As String)
Me.New("welcome")
Console.Write(a & " " & b)
End Sub
End Class
Sub Main()
Dim user1 As User = New User(" to", "tutlane")
Console.WriteLine()
Console.WriteLine("Press Enter Key to Exit..")
Console.ReadLine()
End Sub
End Module
If you observe the above example, we created a different constructors with different parameters and we are calling one constructor from another constructor using Me keyword.
When we execute the above visual basic program, we will get the result as shown below.
If you observe the above result, we are able to call one constructor from another constructor to achieve constructor chaining in a visual basic programming language.
This is how we can achieve constructor chaining in our applications using a visual basic programming language.