Builder

Definition

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

Class Diagram

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
  • includes classes that define the constituent parts, including interfaces for assembling the parts into the final result

Example:

 1    class Vehicle 
 2    {
 3        private string type;
 4        private Dictionary<string, string> parts = new Dictionary<string,string>();
 5
 6        public Vehicle(string type) 
 7        {
 8            this.type = type;
 9        }

        public void AddPart (string key, string value)
        {
            parts.Add(key, value);
        }

        public void Show()
        {
            Console.WriteLine("This is a {0}.", type);
            foreach (string key in parts.Keys) 
            {
                Console.WriteLine("The {0} part is {1}.", key, parts[key]);
            }
            Console.WriteLine("------------------------------------");
        }
    }

 

 1    abstract class VehicleBuilder 
 2    {
 3        protected Vehicle vehicle;
 4
 5        public Vehicle Vechicle 
 6        {
 7            get { return vehicle; }
 8        }
 9
        public abstract void BuildEngine();
        public abstract void BuildFrame();
        public abstract void BuildWheels();
        public abstract void BuildDoors();
    }

 

 1    class MotorcycleBuilder : VehicleBuilder 
 2    {
 3        public MotorcycleBuilder() 
 4        {
 5            vehicle = new Vehicle("motorcycle");
 6        }
 7
 8        public override void BuildDoors()
 9        {
            vehicle.AddPart("doors", "0 doors");
        }

        public override void BuildEngine()
        {
            vehicle.AddPart("engine", "500 cc");
        }

        public override void BuildFrame()
        {
            vehicle.AddPart("frame", "motorcyle frame");
        }

        public override void BuildWheels()
        {
            vehicle.AddPart("wheels", "2 wheels");
        }
    }

 

 1    class CarBuilder : VehicleBuilder
 2    {
 3        public CarBuilder() 
 4        {
 5            vehicle = new Vehicle("car");
 6        }
 7
 8        public override void BuildDoors()
 9        {
            vehicle.AddPart("doors", "2 doors");
        }

        public override void BuildEngine()
        {
            vehicle.AddPart("engine", "2500 cc");
        }

        public override void BuildFrame()
        {
            vehicle.AddPart("frame", "car frame");
        }

        public override void BuildWheels()
        {
            vehicle.AddPart("wheels", "4 wheels");
        }
    }

 

    class Shop
    {
        public void Construct(VehicleBuilder builder) 
        {
            builder.BuildDoors();
            builder.BuildEngine();
            builder.BuildFrame();
            builder.BuildWheels();
        }
    }

 

 1    class Program
 2    {
 3        static void Main(string[] args)
 4        {
 5            Shop shop = new Shop();
 6            MotorcycleBuilder motorcycleBuilder = new MotorcycleBuilder();
 7            CarBuilder carBuilder = new CarBuilder();
 8
 9            shop.Construct(motorcycleBuilder);
            motorcycleBuilder.Vechicle.Show();

            shop.Construct(carBuilder);
            carBuilder.Vechicle.Show();

            Console.Read();
        }
    }