Abstract Factory

The Gang of Four defintion for this design pattern is: "Provide an interface for creating families of related or dependant objects without specifying their concrete classes.".

A VB example of the Abstract Factory Design Pattern

' This code could be run at the page behind level
Dim aCarFactory As CarFactory
' Ideally we would use the Factory Design pattern' but I omitted this for simplicityIf aVariable = "Ford" Then
     aCarFactory = New FordCarFactoryElse
     aCarFactory = New VauxhallCarFactoryEnd If

' Build 2 family carsDim aFamilyCar1 As ICar = aCarFactory.CreateFamilyCarDim aFamilyCar2 As ICar = aCarFactory.CreateFamilyCar

' Build a City CarDim aCityCar As ICar = aCarFactory.CreateCityCar
' The base class Car FactoryPublic MustInherit Class CarFactory
    Public MustOverride Function CreateFamilyCar() As ICar

    Public MustOverride Function CreateCityCar() As ICarEnd Class
' The concrete Ford car factoryPublic Class FordCarFactory
    Inherits CarFactory

    Public Overrides Function CreateCityCar() As ICar
         Return New FordCityCar
    End Function

    Public Overrides Function CreateFamilyCar() As ICar
         Return New FordFamilyCar
    End Function
End Class
' The concrete Vauxhall car factoryPublic Class VauxhallCarFactory
    Inherits CarFactory

    Public Overrides Function CreateCityCar() As ICar
        Return New VauxhallCityCar
    End Function

    Public Overrides Function CreateFamilyCar() As ICar
        Return New VauxhallFamilyCar
    End Function
End Class
' The Car Interface, all cars must implement these methodsPublic Interface ICar

    Sub Drive()    

    Function Desc() As String

End Interface
' The concrete Ford Family CarPublic Class FordFamilyCar
    Implements ICar

    Public Sub Drive() Implements ICar.Drive
       ' Drive car
    End Sub

    Public Function Desc() As String Implements ICar.Desc
       Return "Ford Family Car seats 8"
    End Function
End Class
' The concrete Ford City CarPublic Class FordCityCar
    Implements ICar

    Public Sub Drive() Implements ICar.Drive
       ' Drive car
    End Sub

    Public Function Desc() As String Implements ICar.Desc
       Return "Ford Ciy Car seats 2"
    End Function
End Class
' The concrete Vauxhall City CarPublic Class VauxhallCityCar
    Implements ICar

    Public Sub Drive() Implements ICar.Drive
       ' Drive car
    End Sub

    Public Function Desc() As String Implements ICar.Desc
        Return "Vauxhall Ciy Car seats 4"
    End Function
End Class
' The concrete Vauxhall Family CarPublic Class VauxhallFamilyCar
    Implements ICar

    Public Sub Drive() Implements ICar.Drive
        ' Drive car
    End Sub

    Public Function Desc() As String Implements ICar.Desc
        Return "Vauxhall Family Car seats 6"
    End Function
End Class