Builder Design Pattern

The purpose of Builder Design Pattern is to separate the construction of complex object from its representation so that the same construction process can create different representation. It is usually use in building complex objects by using a step by step approach.

The best practical example I could think is Language Translator. Where there are series of steps involved before language can be translated (such as parsing of text, lexical analysis, grammar, etc) .  But I won’t use this to explain this pattern.

UML Diagram

Figure 1: UML Class Diagram for Builder Design Pattern

Participants

Class/Interface	Description
Director	Uses the ConcreteBuilder. Knows how build. Client code calls directly
Builder	Interface that defines the steps in creating product.
ConcreteBuilder	Provides an implementation interface defined by the builder.  This class can be multiple depending on how many builders will be created. This is where the logic is found.
Product	This is what is being build. Its not a different type, but holds different data. It defines that data to be used by the builder pattern.

Sample Code and Implementation

Let's reinforce this with a real world example using House Builder that involves the participants. Let's get started.

Download Source Code

The Project Structure

UML Class Diagram

Mapping

Design Pattern	House Builder Application
Director	HouseCreator
Builder	IHouseBuilder
ConcreteBuilder	CountryHomeBuilders, DreamBuilers
Product	House

The Codes

The Interface
IHouseBuilder.cs
The Product
House.cs
The ConcreteBuilders
CountryHomeBuilders.cs
DreamBuilders.cs
The Director
HouseCreator.cs

The Client
Program.cs

The Output

Hope this article helpful. Please drop some feedbacks!