DevCity.NET :: Simple Factory Pattern in VB.NET

In this series of upcoming articles I will be discussing how we can implement most of the common and widely used design patterns in .NET.

Patters are broadly classified into 3 categories:

Creational Patterns
Structural Patterns
Behavorial Patterns

This first article in the series explains how we can implement a "Simple Factory" pattern, which falls in of type Creational Patterns.

The Simple Factory Pattern

A Simple Factory pattern is one that returns an instance of one of several possible classes depending on the data provided to it. Usually all of the classes it returns have a common parent class and common methods, but each of them performs a task differently and is optimized for different kinds of data. It is fairly easy to implement a simple factory method using VB.NET

We will build a Simple Factory which accepts the Name of a person and splits it into First name and Last name depending on the format of the name passed for e.g. Bill Gates or Gates,Bill i.e FirstName LastName or LastName,FirstName

The logic to split the full name would be built in two classes FirstFirst and LastLast whose instance would be created by the simplefactory class depending on the name format passed. We will create a base class, which will have two functions getFirst and getLast to get the FirstName and LastName respectively.

Imports System
Imports Microsoft.VisualBasic

    Public Class NameClass
    Protected Lname, Frname As String

    Public Function getFirst() As String
        Return Frname
    End Function
    
    Public Function getLast() As String
        Return Lname
    End Function

End Class

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Then, we create a FirstFirst class which has a logic to split the name if it is in the format "Bill Gates", this class derives from the Name class.

Public Class FirstFirst

    Inherits NameClass

    Public Sub New(ByVal nm As String)
    Dim arr() As String

        arr = Split(nm, " ")
        Frname = arr(0)
        Lname = arr(1)

    End Sub

End Class

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The next step is to create the LastLast class which has a logic to split the name if it is in the format "Gates,Bill", this class also derives from the Name class.

Public Class LastLast

    Inherits NameClass

    Public Sub New(ByVal nm As String)
    Dim arr() As String

        arr = Split(nm, ",")
        Frname = arr(1)
        Lname = arr(0)

    End Sub

End Class

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Our final step is to create the Simple Factory class which will accept the Name and decide instance of which of the two derived classes will be created.

Public Class SimpleFactory
    Shared Sub main()
    Dim strName As String
    Dim o As NameClass
        Console.WriteLine("Name")
        strName = Console.ReadLine
        If strName Like ("*,*") Then
            o = New LastLast(strName)
            MsgBox(o.getFirst)
            MsgBox(o.getLast)
        Else
            o = New FirstFirst(strName) 
            MsgBox(o.getFirst) 
            MsgBox(o.getLast)
        End If
    End Sub
End Class

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Copy all the codes in a single file SimpleFactory.vb and compile as

vbc SimpleFactory.vb

Execute the SimpleFactory.exe and supply the name in the formats Bill Gates and Gates,Bill
What you will notice is the factory class determines the input and decides which object to create.

Related links: http://www.dotnetextreme.com