Builder Design Pattern



Click here for larger image

Environment: Win2K, NT

Creational Pattern Builder

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

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 objects 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 thats 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.


C#

using System;
using System.Collections;

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

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

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

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.Discription());
  }
}

Visual Basic .NET

Imports System
Imports System.Collections
Imports Microsoft.VisualBasic

Public Interface IHouse
    Function GetBackyard() As Boolean
    Function NoOfRooms() As Long
    Function Discription() 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 Discription() As String _
                      Implements IHouse.Discription
        Dim myEnumerator As IDictionaryEnumerator = _
                              Rooms.GetEnumerator
        Dim strDiscription As String
        strDiscription = "This is an Apartment with " &_
                   Rooms.Count & " Rooms " & vbLf
        strDiscription = strDiscription & _
                "This Apartment doesn't have a backyard" & _
                vbLf
        With myEnumerator
            While .MoveNext
                strDiscription = strDiscription & _
                vbLf & .Key & vbTab & _
                .Value.RoomName
            End While
        End With
        Discription = strDiscription
    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 Discription() As String _
                  Implements IHouse.Discription
       Dim myEnumerator As IDictionaryEnumerator = _
                              Rooms.GetEnumerator
       Dim strDiscription As String
       strDiscription = "This is an Single Family Home with " & _
                        Rooms.Count & _
                        " Rooms " & vbLf
       strDiscription = strDiscription & _
                 "This house has a backyard" & vbLf
       With myEnumerator
           While .MoveNext
               strDiscription = strDiscription & _
               vbLf & .Key & vbTab & _
               .Value.RoomName
           End While
       End With
       Discription = strDiscription
   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 Boolean) As 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(.Discription)
      End With
   End sub
End class

About the Author

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.

Downloads

Download demo project - 2 Kb


Comments

  • I don't figure out any difference betwwen Builder vs Factory

    Posted by Legacy on 02/20/2002 12:00am

    Originally posted by: robin

    I don't figure out any difference betwwen Builder vs Factory in your two examples.

    Reply
Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Live Event Date: September 17, 2014 @ 1:00 p.m. ET / 10:00 a.m. PT Another day, another end-of-support deadline. You've heard enough about the hazards of not migrating to Windows Server 2008 or 2012. What you may not know is that there's plenty in it for you and your business, like increased automation and performance, time-saving technical features, and a lower total cost of ownership. Check out this upcoming eSeminar and join Rich Holmes, Pomeroy's practice director of virtualization, as he discusses the …

  • Live Event Date: September 16, 2014 @ 11:00 a.m. ET / 8:00 a.m. PT Are you starting an on-premise-to-cloud data migration project? Have you thought about how much space you might need for your online platform or how to handle data that might be related to users who no longer exist? If these questions or any other concerns have been plaguing you about your migration project, check out this eSeminar. Join our speakers Betsy Bilhorn, VP, Product Management at Scribe, Mike Virnig, PowerSucess Manager and Michele …

Most Popular Programming Stories

More for Developers

Latest Developer Headlines

RSS Feeds