Chapter 6 Creational Patterns: Builder

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Chapter 6 -Creational Patterns Builder
CIS 476/566 Software Architecture and Design
Patterns

• Dr. Brahim Medjahed
• brahim_at_umich.edu

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Design Patterns in GoF The Big Picture
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Builder Pattern - Intent

• Separate the construction of a complex object
  from its representation so that the same
  construction process can create different
  representations.
• The client is shielded from the details of the
  objects construction.

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Builder - Example

• Client wants to buy a new vehicle (product)
• He has a choice between mini-van, sports car and
  motorcycle.
• Client isnt concerned about the building of his
  vehicle but has features (parts) that he wants.
• Parts includes doors, tires, seats
• They are constructed differently for each
  different vehicle.
• Builder class constructs the vehicle by building
  each part and putting them all together.

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Builder - Applicability

• The algorithm for creating a complex object needs
  to be independent of the parts that make up the
  object.
• The construction process must allow different
  representations for the object being built.

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Builder UML Class Diagram
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Builder Participants

• Builder  
• Specifies an abstract interface for creating
  parts of a Product object
• ConcreteBuilder  
• Constructs and assembles parts of the product by
  implementing the Builder interface
• Defines and keeps track of the representation it
  creates
• Provides an interface for retrieving the product
• Director  
• Constructs an object using the Builder interface
• Product 
• Represents the complex object under construction.
  
• ConcreteBuilder builds the product's internal
  representation and defines the process by which
  it's assembled

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Builder - Collaborations

• The client creates the Director object and
  configures it with the desired Builder object.
• Director notifies the builder whenever a part of
  the product should be built.
• Builder handles requests from the director and
  adds parts to the product.
• The client retrieves the final product from the
  builder.

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Builder UML Sequence Diagram
aClient
aDirector
aConcreteBuilder
New ConcreteBuilder
New Director(aConcreteBuilder)
Construct()
BuildPartA()
BuildPartB()
BuildPartC()
GetResult()
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Builder - Consequences

• Allows for variations in a products internal
  representation since the Director uses an
  abstract interface.
• Isolates code for construction and
  representation.
• Gives finer control over the construction
  process. The director builds each product in a
  step-by-step manner.

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Builder Example

• Product has three possible parts Part1, Part2,
  and Part3 (all integer)
• We have two concrete builders ConcreteBuilder1
  and ConcreteBuilder2
• ConcreteBuilder1 assign 11, 12, and 13 tp Part1,
  Part2, and Part3 respectively
• ConcreteBuilder2 assign 21, 22, and 23 tp Part1,
  Part2, and Part3 respectively

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Example UML Class Diagram

• To be done in class

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Example - Implementation

• // "Director"   class Director       //
  Builder uses a complex series of steps
      public void Construct(Builder
  builder)          builder.BuildPart1()      b
  uilder.BuildPart2()
• builder.BuildPart3()
•       

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Example Implementation (contd)

• // "Builder" abstract class Builder      publi
  c abstract void BuildPart1()    public abstract
  void BuildPart2()
• public abstract void BuildPart3()
•      public abstract Product
  GetResult()  
• // "Product" class Product      public
  part1,part2, part3 integer
•   

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Example Implementation (contd)

• // "ConcreteBuilder1"   class ConcreteBuilder1
  Builder      private Product product new
  Product()    public override void
  BuildPart1()          product.part1
  11       public override void
  BuildPart2()          product.part2
  12     public override void
  BuildPart3()          product.part3
  13        public override Product
  GetResult()          return product      

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Example Implementation (contd)

• // "ConcreteBuilder2"   class ConcreteBuilder2
  Builder      private Product product new
  Product()    public override void
  BuildPart1()          product.part1
  21       public override void
  BuildPart2()          product.part2
  22     public override void
  BuildPart3()          product.part3
  23        public override Product
  GetResult()          return product      

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Example Implementation (contd)

• public class Client      public static void
  Main()           // Create director and
  builders       Director mydirector new
  Director()      Builder b1 new
  ConcreteBuilder1()      Builder b2 new
  ConcreteBuilder2()      // Construct two
  products       mydirector.Construct(b1)      Pr
  oduct p1 b1.GetResult()            mydirector
  .Construct(b2)      Product p2
  b2.GetResult()       

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Example UML Sequence Diagram

• To be done in class