How to implement a class when it is defined in an interface? - vb.net

Question

An interface can have a class in it but I do not understand how to implement such an interface. I give an example below:
I wrote the following simple code without any interface:
Imports System
Module Program
Sub Main()
Dim n As New name("Mounisha", "Ghosh")
Dim student As New Student(n, 14)
Console.WriteLine("First Name: {0}", student.studentName.firstName)
Console.WriteLine("Last Name: {0}", student.studentName.lastName)
Console.WriteLine("Age: {0}", student.age)
Console.ReadLine()
End Sub
End Module
Class name
Public Property firstName As String
Public Property lastName As String
Sub New(ByVal f As String, ByVal l As String)
firstName = f
lastName = l
End Sub
End Class
Class Student
Private nameValue As name
Public ReadOnly Property studentName() As name
Get
Return nameValue
End Get
End Property
Public Property age As Integer
Sub New(ByVal n As name, ByVal a As Integer)
nameValue = n
age = a
End Sub
End Class
Then I tried to re-organize by putting the class name in an interface and implement it in the class student. But I was not able to construct my code. I give the overall idea of the code I am trying to construct below:
Imports System
Interface IClass
Class name
Public Property firstName As String
Public Property lastName As String
Sub New(ByVal f As String, ByVal l As String)
firstName = f
lastName = l
End Sub
End Class
End Interface
Module Program
Sub Main()
'How to create instances and pass values to constructors?
End Sub
End Module
Class Student : Implements IClass
'The idea is to create a readonly property of type "name"
'But not able to use the Interface to do the same
Public Property age As Integer
End Class
The main idea is to understand how to implement an interface with a class in it. Pls help.
The other point I want to highlight is that in the constructor of the class name I have written End Sub. Now we cannot use the end sub statement in interface - so why am I not getting an error? Also do the statements firstName = f and lastName = l not denote an implementation which should have been flagged as an error by the compiler - but not getting any error. Any explanations for this?

Answer 1

What you're doing is simply adding a nested class to the interface. This isn't seen as something that the implementing class has to implement but instead is just a class available via that interface. Using your structure, in order to require Student to implement a read only name property, you have to add that property to the interface.
Public Interface IClass
ReadOnly Property Fullname As Name
Class Name
Public Property FirstName As String
Public Property LastName As String
Sub New(firstName As String, lastName As String)
Me.FirstName = firstName
Me.LastName = lastName
End Sub
End Class
End Interface
Your Student Class would then look like
Public Class Student : Implements IClass
'Because Name is nested within IClass, it's referenced by IClass.Name
Public ReadOnly Property Fullname As IClass.Name Implements IClass.Fullname
Public Property Age As Integer
Public Sub New(name As IClass.Name, age As Integer)
Fullname = name
Me.Age = age
End Sub
End Class
And creating a student would be
Dim name = New IClass.Name("Mounisha", "Ghosh") 'again we access name via the interface
Dim student = New Student(name, 14)
Usually you would not add a nested Class to the interface but instead do something like
Module Program
Sub Main()
Dim studuent = New Student(New Name("Mounisha", "Ghosh"), 14)
End Sub
End Module
Interface IClass
ReadOnly Property Fullname As Name
End Interface
Public Class Name
Public Property FirstName As String
Public Property LastName As String
Sub New(firstName As String, lastName As String)
Me.FirstName = firstName
Me.LastName = lastName
End Sub
End Class
Class Student : Implements IClass
Public ReadOnly Property Fullname As Name Implements IClass.Fullname
Public Property Age As Integer
Public Sub New(name As Name, age As Integer)
Fullname = name
Me.Age = age
End Sub
End Class