Object-Oriented Programming (OOP)

Abstract Class


An abstract class is created for the purpose of being inherited. We cannot create objects from the abstract class. You must add the keyword MustInherit before the class AbsAnimal to make it abstract. MustOveride keywords are used to make methods abstract. Methods in derived class must use Overrides keywords to override the methods of its abstract base class.


Example:
Module Module1
 
    Sub Main()
        Dim d As New Dog
        d.setnumberOflegs(4) 'setnumberOflegs was inherited from the Animal class
        d.setdogName("Aluk")
        Console.WriteLine("Dog Name: " & d.getdogName())
        Console.WriteLine("Number of legs: " & d.getnumberOflegs())
        'getnumberOflegs was inherited from the Animal class
 
        Console.ReadLine()
    End Sub
 
    Class Animal : Inherits AbsAnimal 'inherit abstract class
 
        Private numberOflegs As Integer
 
        Public Overrides Sub setnumberOflegs(ByVal n As Integer) ' override abstract method
 
            numberOflegs = n
        End Sub
 
        Public Overrides Function getnumberOflegs() As Integer ' override abstract method
            getnumberOflegs = numberOflegs
 
        End Function
 
    End Class
 
    Class Dog : Inherits Animal
 
        Private dogName As String
 
        Public Sub setdogName(ByVal name As String)
 
            dogName = name
 
        End Sub
        Public Function getdogName() As String
 
            getdogName = dogName
        End Function
 
    End Class
 
    MustInherit Class AbsAnimal
 
        Public MustOverride Sub setnumberOflegs(ByVal n As Integer)
 
        Public MustOverride Function getnumberOflegs() As Integer
 
 
    End Class
 
End Module




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