.NET Design Patterns

Builder


 Definition
 UML diagram
 Participants
 Structural code in C#
 Real-world code in C#
 .NET Optimized code in C#



Definition

Separate the construction of a complex object from its representation so that the same construction process can create different representations.

Frequency of use:
Medium low




UML class diagram






Participants


    The classes and objects participating in this pattern are:

  • Builder  (VehicleBuilder)
    • specifies an abstract interface for creating parts of a Product object
  • ConcreteBuilder  (MotorCycleBuilder, CarBuilder, ScooterBuilder)
    • 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  (Shop)
    • constructs an object using the Builder interface
  • Product  (Vehicle)
    • represents the complex object under construction. ConcreteBuilder builds the product's internal representation and defines the process by which it's assembled
    • includes classes that define the constituent parts, including interfaces for assembling the parts into the final result



Structural code in C#


This structural code demonstrates the Builder pattern in which complex objects are created in a step-by-step fashion. The construction process can create different object representations and provides a high level of control over the assembly of the objects.

                 

using System;

using System.Collections.Generic;

 

namespace DoFactory.GangOfFour.Builder.Structural

{

  /// <summary>

  /// MainApp startup class for Structural

  /// Builder Design Pattern.

  /// </summary>

  public class MainApp

  {

    /// <summary>

    /// Entry point into console application.

    /// </summary>

    public static void Main()

    {

      // Create director and builders

      Director director = new Director();

 

      Builder b1 = new ConcreteBuilder1();

      Builder b2 = new ConcreteBuilder2();

 

      // Construct two products

      director.Construct(b1);

      Product p1 = b1.GetResult();

      p1.Show();

 

      director.Construct(b2);

      Product p2 = b2.GetResult();

      p2.Show();

 

      // Wait for user

      Console.ReadKey();

    }

  }

 

  /// <summary>

  /// The 'Director' class

  /// </summary>

  class Director

  {

    // Builder uses a complex series of steps

    public void Construct(Builder builder)

    {

      builder.BuildPartA();

      builder.BuildPartB();

    }

  }

 

  /// <summary>

  /// The 'Builder' abstract class

  /// </summary>

  abstract class Builder

  {

    public abstract void BuildPartA();

    public abstract void BuildPartB();

    public abstract Product GetResult();

  }

 

  /// <summary>

  /// The 'ConcreteBuilder1' class

  /// </summary>

  class ConcreteBuilder1 : Builder

  {

    private Product _product = new Product();

 

    public override void BuildPartA()

    {

      _product.Add("PartA");

    }

 

    public override void BuildPartB()

    {

      _product.Add("PartB");

    }

 

    public override Product GetResult()

    {

      return _product;

    }

  }

 

  /// <summary>

  /// The 'ConcreteBuilder2' class

  /// </summary>

  class ConcreteBuilder2 : Builder

  {

    private Product _product = new Product();

 

    public override void BuildPartA()

    {

      _product.Add("PartX");

    }

 

    public override void BuildPartB()

    {

      _product.Add("PartY");

    }

 

    public override Product GetResult()

    {

      return _product;

    }

  }

 

  /// <summary>

  /// The 'Product' class

  /// </summary>

  class Product

  {

    private List<string> _parts = new List<string>();

 

    public void Add(string part)

    {

      _parts.Add(part);

    }

 

    public void Show()

    {

      Console.WriteLine("\nProduct Parts -------");

      foreach (string part in _parts)

        Console.WriteLine(part);

    }

  }

}


Output
Product Parts -------
PartA
PartB

Product Parts -------
PartX
PartY




Real-world code in C#


This real-world code demonstates the Builder pattern in which different vehicles are assembled in a step-by-step fashion. The Shop uses VehicleBuilders to construct a variety of Vehicles in a series of sequential steps.

                 

using System;

using System.Collections.Generic;

 

namespace DoFactory.GangOfFour.Builder.RealWorld

{

  /// <summary>

  /// MainApp startup class for Real-World

  /// Builder Design Pattern.

  /// </summary>

  public class MainApp

  {

    /// <summary>

    /// Entry point into console application.

    /// </summary>

    public static void Main()

    {

      VehicleBuilder builder;

 

      // Create shop with vehicle builders

      Shop shop = new Shop();

 

      // Construct and display vehicles

      builder = new ScooterBuilder();

      shop.Construct(builder);

      builder.Vehicle.Show();

 

      builder = new CarBuilder();

      shop.Construct(builder);

      builder.Vehicle.Show();

 

      builder = new MotorCycleBuilder();

      shop.Construct(builder);

      builder.Vehicle.Show();

 

      // Wait for user

      Console.ReadKey();

    }

  }

 

  /// <summary>

  /// The 'Director' class

  /// </summary>

  class Shop

  {

    // Builder uses a complex series of steps

    public void Construct(VehicleBuilder vehicleBuilder)

    {

      vehicleBuilder.BuildFrame();

      vehicleBuilder.BuildEngine();

      vehicleBuilder.BuildWheels();

      vehicleBuilder.BuildDoors();

    }

  }

 

  /// <summary>

  /// The 'Builder' abstract class

  /// </summary>

  abstract class VehicleBuilder

  {

    protected Vehicle vehicle;

 

    // Gets vehicle instance

    public Vehicle Vehicle

    {

      get { return vehicle; }

    }

 

    // Abstract build methods

    public abstract void BuildFrame();

    public abstract void BuildEngine();

    public abstract void BuildWheels();

    public abstract void BuildDoors();

  }

 

  /// <summary>

  /// The 'ConcreteBuilder1' class

  /// </summary>

  class MotorCycleBuilder : VehicleBuilder

  {

    public MotorCycleBuilder()

    {

      vehicle = new Vehicle("MotorCycle");

    }

 

    public override void BuildFrame()

    {

      vehicle["frame"] = "MotorCycle Frame";

    }

 

    public override void BuildEngine()

    {

      vehicle["engine"] = "500 cc";

    }

 

    public override void BuildWheels()

    {

      vehicle["wheels"] = "2";

    }

 

    public override void BuildDoors()

    {

      vehicle["doors"] = "0";

    }

  }

 

 

  /// <summary>

  /// The 'ConcreteBuilder2' class

  /// </summary>

  class CarBuilder : VehicleBuilder

  {

    public CarBuilder()

    {

      vehicle = new Vehicle("Car");

    }

 

    public override void BuildFrame()

    {

      vehicle["frame"] = "Car Frame";

    }

 

    public override void BuildEngine()

    {

      vehicle["engine"] = "2500 cc";

    }

 

    public override void BuildWheels()

    {

      vehicle["wheels"] = "4";

    }

 

    public override void BuildDoors()

    {

      vehicle["doors"] = "4";

    }

  }

 

  /// <summary>

  /// The 'ConcreteBuilder3' class

  /// </summary>

  class ScooterBuilder : VehicleBuilder

  {

    public ScooterBuilder()

    {

      vehicle = new Vehicle("Scooter");

    }

 

    public override void BuildFrame()

    {

      vehicle["frame"] = "Scooter Frame";

    }

 

    public override void BuildEngine()

    {

      vehicle["engine"] = "50 cc";

    }

 

    public override void BuildWheels()

    {

      vehicle["wheels"] = "2";

    }

 

    public override void BuildDoors()

    {

      vehicle["doors"] = "0";

    }

  }

 

  /// <summary>

  /// The 'Product' class

  /// </summary>

  class Vehicle

  {

    private string _vehicleType;

    private Dictionary<string,string> _parts =

      new Dictionary<string,string>();

 

    // Constructor

    public Vehicle(string vehicleType)

    {

      this._vehicleType = vehicleType;

    }

 

    // Indexer

    public string this[string key]

    {

      get { return _parts[key]; }

      set { _parts[key] = value; }

    }

 

    public void Show()

    {

      Console.WriteLine("\n---------------------------");

      Console.WriteLine("Vehicle Type: {0}", _vehicleType);

      Console.WriteLine(" Frame : {0}", _parts["frame"]);

      Console.WriteLine(" Engine : {0}", _parts["engine"]);

      Console.WriteLine(" #Wheels: {0}", _parts["wheels"]);

      Console.WriteLine(" #Doors : {0}", _parts["doors"]);

    }

  }

}

 


Output
---------------------------
Vehicle Type: Scooter
 Frame  : Scooter Frame
 Engine : none
 #Wheels: 2
 #Doors : 0

---------------------------
Vehicle Type: Car
 Frame  : Car Frame
 Engine : 2500 cc
 #Wheels: 4
 #Doors : 4

---------------------------
Vehicle Type: MotorCycle
 Frame  : MotorCycle Frame
 Engine : 500 cc
 #Wheels: 2
 #Doors : 0




.NET Optimized code in C#


The .NET optimized code demonstrates the same real-world situation as above but uses modern, built-in .NET features, such as, generics, reflection, object initializers, automatic properties, etc. You can find an example on our Singleton pattern page.

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