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Builder Design Pattern Implementation in C# and VB.NET
by Ashish Jaiman | Published  02/24/2002 | Windows Development | Rating:
Ashish Jaiman

Ashish works as a Sr. Software Developer with Lexign Inc., an end-to-end trusted electronic transaction management software provider (http://www.lexign.com).

Ashish has 6 years of experience in designing and developing distributed systems, server technologies and web based software applications using Microsoft technologies, Java, XML and .NET. He holds MCSD (Microsoft Certified Software Developer) and SCJP (Sun Certified Java Programmer) certifications.

Contact Ashish at jaimanalwar@yahoo.com or ashish.jaiman@lexign.com.

 

View all articles by Ashish Jaiman...
Builder Design Pattern Implementation in C# and VB.NET

Article source code: builder.zip

The Builder pattern allows a client object to construct a complex object by specifying only its type and content. The client is shielded from the details of the object’s construction.

It is a pattern for step-by-step creation of a complex object so that the same construction process can create different representations is the routine in the builder pattern that also makes for finer control over the construction process. All the different builders generally inherit from an abstract builder class that declares the general functions to be used by the director to let the builder create the product in parts.

Builder has a similar motivation to the abstract factory but, whereas in that pattern, the client uses the abstract factory class methods to create its own object, in Builder the client instructs the builder class on how to create the object and then asks it for the result. How the class is put together is up to the Builder class. It's a subtle difference.

The Builder pattern is applicable when the algorithm for creating a complex object should be independent of the parts that make up the object and how they are assembled and the construction process must allow different representations for the object that’s constructed

Example

Below is an example of creating a House, the clients asks the Director (CDirector class) to create a House by calling BuildHouse method which takes a boolean parameter (blnBackyard), the director then creates an Apartment (Concrete Builder) if the blnBackyard is false or a Single Family Home (Concrete Builder) if the blnBackyard is true (both of them implements IHouse interface) and returns IHouse (Abstract Builder) Interface.

The director does the complex building of a House and the client gets back IHouse interface that it codes against without worrying about the creation of House, Rooms, backyard etc.

Diagram

C# Implementation

using System;
using System.Collections;

public interface IHouse
{
    bool GetBackyard();
    long NoOfRooms();
    string  Description();
}

public class CApt:IHouse
{
    private bool mblnBackyard;
    private Hashtable Rooms;

    public CApt()
    {
        CRoom room;
        Rooms = new Hashtable();
        room = new CRoom();
        room.RoomName = "Master Bedroom";
        Rooms.Add ("room1",room);

        room = new CRoom();
        room.RoomName = "Second Bedroom";
        Rooms.Add ("room2",room);

        room = new CRoom();
        room.RoomName = "Living Room";
        Rooms.Add ("room3",room);

        mblnBackyard = false;
    }

    public bool GetBackyard()
    {
        return mblnBackyard;
    }

    public long NoOfRooms()
    {
        return Rooms.Count;
    }

    public string  Description()
    {
        IDictionaryEnumerator myEnumerator  = Rooms.GetEnumerator();
        string strDescription;
        strDescription = "This is an Apartment with " + Rooms.Count +
                         " Rooms \n";
        strDescription = strDescription + "This Apartment doesn't have " +
                         "a backyard \n";
        while (myEnumerator.MoveNext())
        {
            strDescription = strDescription + "\n" + myEnumerator.Key + "\t"
                             + ((CRoom)myEnumerator.Value).RoomName;
        }
        return strDescription;
    }
}

public class CSFH:IHouse
{  
    private bool mblnBackyard;
    private Hashtable Rooms;

    public CSFH()
    {
        CRoom room;
        Rooms = new Hashtable();

        room = new CRoom();
        room.RoomName = "Master Bedroom";
        Rooms.Add ("room1",room);

        room = new CRoom();
        room.RoomName = "Second Bedroom";
        Rooms.Add ("room2",room);

        room = new CRoom();
        room.RoomName = "Third Room";
        Rooms.Add ("room3",room);

        room = new CRoom();
        room.RoomName = "Living Room";
        Rooms.Add ("room4",room);

        room = new CRoom();
        room.RoomName = "Guest Room";
        Rooms.Add ("room5",room);

        mblnBackyard = true;

    }

    public bool GetBackyard()
    {
        return mblnBackyard;
    }

    public long NoOfRooms()
    {
        return Rooms.Count;
    }

    public string  Description()
    {
        IDictionaryEnumerator myEnumerator  = Rooms.GetEnumerator();
        string strDescription;
        strDescription = "This is an Single Family Home with " + Rooms.Count
                         + " Rooms \n";
        strDescription = strDescription + "This house has a backyard \n";
        while (myEnumerator.MoveNext())
        {
            strDescription = strDescription + "\n" + myEnumerator.Key + "\t"
                             + ((CRoom)myEnumerator.Value).RoomName;
        }
        return strDescription;
    }
}

public interface IRoom
{
    string RoomName{get;set;}
}

public class CRoom:IRoom
{
    private string mstrRoomName;
    public string RoomName
    {
        get
        {
            return mstrRoomName;
        }
        set
        {
            mstrRoomName = value;
        }
    }
}

public class CDirector
{
    public IHouse BuildHouse(bool blnBackyard)
    {
        if (blnBackyard)
        {
            return new CSFH();
        }
        else
        {
            return new CApt();
        }
    }
}

public class Client
{
    static void Main(string[] args)
    {
        CDirector objDirector = new CDirector();
        IHouse objHouse;
        objHouse = objDirector.BuildHouse(bool.Parse(args[0]));
        Console.WriteLine(objHouse.Description());
    }
}

VB.NET Implementation

Imports System
Imports System.Collections Imports Microsoft.VisualBasic Public Interface IHouse     Function GetBackyard() As Boolean     Function NoOfRooms() As Long     Function Description() As String End Interface Public Class CApt     Implements IHouse     Private blnBackYard As Boolean     Private Rooms As Hashtable     Sub New()         Dim room As CRoom         Rooms = New Hashtable()         room = New CRoom()         room.RoomName = "Master Bedroom"         Rooms.Add("room1"room)         room = New CRoom()         room.RoomName = "Second Bedroom"         Rooms.Add("room2"room)         room = New CRoom()         room.RoomName = "Living Room"         Rooms.Add("room3"room)         blnBackYard = False     End Sub     Public Function GetBackyard() As Boolean Implements IHouse.GetBackyard         GetBackyard = blnBackYard     End Function     Public Function NoOfRooms() As Long Implements IHouse.NoOfRooms         NoOfRooms = Rooms.Count     End Function     Public Function Description() As String Implements IHouse.Description         Dim myEnumerator As IDictionaryEnumerator = Rooms.GetEnumerator         Dim strDescription As String         strDescription = "This is an Apartment with " & Rooms.Count & _                          " Rooms " & vbLf         strDescription = strDescription & "This Apartment doesn't have a " & _                  "backyard" & vbLf         With myEnumerator             While .MoveNext                 strDescription = strDescription & vbLf & .Key & vbTab & _                  .Value.RoomName             End While         End With         Description = strDescription     End Function End Class Public Class CSFH     Implements IHouse     Private blnBackYard As Boolean     Private Rooms As Hashtable     Sub New()         Dim room As CRoom         Rooms = New Hashtable()         room = New CRoom()         room.RoomName = "Master Bedroom"         Rooms.Add("room1"room)         room = New CRoom()         room.RoomName = "Second Bedroom"         Rooms.Add("room2"room)         room = New CRoom()         room.RoomName = "Third Room"         Rooms.Add("room3"room)         room = New CRoom()         room.RoomName = "Living Room"         Rooms.Add("room4"room)         room = New CRoom()         room.RoomName = "Guest Room"         Rooms.Add("room5"room)         blnBackYard = True     End Sub     Public Function GetBackyard() As Boolean Implements IHouse.GetBackyard         GetBackyard = blnBackYard     End Function     Public Function NoOfRooms() As Long Implements IHouse.NoOfRooms         NoOfRooms = Rooms.Count     End Function     Public Function Description() As String Implements IHouse.Description         Dim myEnumerator As IDictionaryEnumerator = Rooms.GetEnumerator         Dim strDescription As String         strDescription = "This is an Single Family Home with " & Rooms.Count _                  & " Rooms " & vbLf         strDescription = strDescription & "This house has a backyard" & vbLf         With myEnumerator             While .MoveNext                 strDescription = strDescription & vbLf & .Key & vbTab _                  & .Value.RoomName             End While         End With         Description = strDescription     End Function End Class Public Interface IRoom     Property RoomName() As String End Interface Public Class CRoom     Implements IRoom     Private mstrRoomName As String     Public Property RoomName() As String Implements IRoom.RoomName         Get             RoomName = mstrRoomName         End Get         Set(ByVal value As String)             mstrRoomName = value         End Set     End Property End Class Public Class CDirector     Public Function BuildHouse(ByVal blnBackyard As BooleanAs IHouse         If blnBackyard Then             BuildHouse = New CSFH()         Else             BuildHouse = New CApt()         End If     End Function End Class Public Class Client     Public Shared Sub Main(ByVal args() as String)         Dim objDirector As New CDirector()         Dim objHouse as IHouse         objHouse = objDirector.BuildHouse(args(0))         With objHouse             Console.WriteLine(.Description)         End With     End Sub End Class
Generated using PrettyCode.Encoder

Reference: E. Gamma et al., "Design Patterns: Elements of Reusable Object-Oriented Software"
ISBN 0-201-63361-2, Addison Wesley, 1995.

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