Builder Pattern

Builder pattern is useful when application needs to create complex object or structure. Builder pattern falls under creational pattern of GOF (Gang of Four) Pattern.

When to use –

Builder Pattern can be implemented in your application when you want to create objects which involves multiple steps or customized user request. With the use of builder pattern, client doesn’t know how object are created inside or how many steps are involved to create an object. Builder Pattern keeps construction logic separate from client.

Major components of Builder Pattern –

Builder – Specifies steps to create product. This is an interface.

Concrete Builder – Create complex product and parts of products via implementing the Builder interface.

Director – This class used to construct an object using Builder interface.

Product – This class represents actual product object which is constructed by the builder pattern.

Let’s say user wants to buy Android mobile phone. Many companies are making Android mobile phones with different specifications. User wants Android mobile which is end product for him or her but specification may vary like processor, ram, screen size, battery capacity etc. See below example how Builder Pattern can be useful to user to get Android mobile phone.

Code –

public enum MobileType

{

    Samsung,

    LG

}

//Builder Interface

public interface IMobileBuilder

{

    void SetModelName(string modelName);

    void SetOperatingSystem(string operatingSystem);

    void SetRAM(string ram);

    void SetProcessor(string processor);

    void SetBattery(string battery);

    void SetScreenSize(string screenSize);

    Mobile GetMobile();

}

//Product class

public class Mobile

{

    public string ModelName { get; set; }

    public string OperatingSystem { get; set; }

    public string RAM { get; set; }

    public string Processor { get; set; }

    public string Battery { get; set; }

    public string ScreenSize { get; set; }

    public override string ToString()

    {

        StringBuilder sb = new StringBuilder();

        sb.Append("--------------------------------------------\n");

        sb.Append(string.Format("Model Name - {0},\n", ModelName));

        sb.Append(string.Format("Operating System - {0},\n", OperatingSystem));

        sb.Append(string.Format("RAM - {0},\n", RAM));

        sb.Append(string.Format("Processor - {0},\n", Processor));

        sb.Append(string.Format("Battery - {0},\n", Battery));

        sb.Append(string.Format("Screen Size - {0}\n", ScreenSize));

        sb.Append("--------------------------------------------");

        return sb.ToString();

    }

}

//Concrete Builder

public class AndroidMobileBuilder : IMobileBuilder

{

    Mobile mobile = new Mobile();

       

    public void SetBattery(string battery)

    {

        mobile.Battery = battery;

    }

    public void SetModelName(string modelName)

    {

        mobile.ModelName = modelName;

    }

    public void SetOperatingSystem(string operatingSystem)

    {

        mobile.OperatingSystem = operatingSystem;

    }

    public void SetProcessor(string processor)

    {

        mobile.Processor = processor;

    }

    public void SetRAM(string ram)

    {

        mobile.RAM = ram;

    }

    public void SetScreenSize(string screenSize)

    {

        mobile.ScreenSize = screenSize;

    }

    public Mobile GetMobile()

    {

        return mobile;

    }

}

//Director class

public class MobileCreator

{

    public static IMobileBuilder BuildMobile(MobileType mobileType)

    {

        switch (mobileType)

        {

            case MobileType.Samsung:

                AndroidMobileBuilder androidMobile1 = new AndroidMobileBuilder();

                androidMobile1.SetBattery("3000mah");

                androidMobile1.SetModelName("Samsung Galaxy S5");

                androidMobile1.SetOperatingSystem("Android JellyBean 4.1");

                androidMobile1.SetProcessor("Snap Dragon 1.5Mhz");

                androidMobile1.SetRAM("2 GB");

                androidMobile1.SetScreenSize("5.5 inch");

                return androidMobile1;

            case MobileType.LG:

                AndroidMobileBuilder androidMobile2 = new AndroidMobileBuilder();

                androidMobile2.SetBattery("3200mah");

                androidMobile2.SetModelName("LG Optimus G Pro2");

                androidMobile2.SetOperatingSystem("Android Lollipop 5.1");

                androidMobile2.SetProcessor("Snap Dragon 1.8Mhz");

                androidMobile2.SetRAM("3 GB");

                androidMobile2.SetScreenSize("5.7 inch");

                return androidMobile2;

            default:

                break;

        }

        return null;

    }

}

class Program

{

    static void Main(string[] args)

    {

        //Create and returns Samsung mobile object

        IMobileBuilder mobileBuilder = MobileCreator.BuildMobile(MobileType.Samsung);

        Mobile m = mobileBuilder.GetMobile();

        Console.WriteLine(m.ToString());

        //Create and returns LG mobile object

        mobileBuilder = MobileCreator.BuildMobile(MobileType.LG);

        m = mobileBuilder.GetMobile();

        Console.WriteLine(m.ToString());

        Console.ReadLine();

    }

}

Output –

In above example, user can get Android mobile phone of Samsung/LG brand as per mobile phone’s specifications. This code is written to build mobile phone as per standard specification provided by manufacturer but you can modify code to enter user inputs to build mobile phone device as per user requirement.

Advantages –

• Encourage code encapsulation for separating construction logic from its client.
• Easy to extend and maintain.
• Gives you more control to construction process.
• More robust as fully constructed object available to the client.

Disadvantages –

• Builder Pattern requires some code duplication via implementing different products.

Difference between Abstract Factory and Builder Pattern –

Abstract Factory Pattern	Builder Pattern
Focuses on what to build	Focuses on how to build
Depends on other factories to construct object.	Constructs complex object step by step manner.
Builds different types of products from different factories.	Builds complex product.

Hope this article helpful to you. Please leave your feedback in comments below.

References –

MSDN

DoFactory

See Also – 

Creational Patterns	Structural Patterns	Behavioral Patterns
Singleton Pattern	Adapter Pattern	Chain of Responsibility Pattern
Thread safe singleton pattern	Bridge Pattern	Command Pattern
Factory Pattern	Composite Pattern	Interpreter Pattern
Abstract Factory Pattern	Decorator Pattern	Iterator Pattern
Builder Pattern	Facade Pattern	Mediator Pattern
Prototype Pattern	Flyweight Pattern	Memento Pattern
	Proxy Pattern	Observer Pattern
		State Pattern
		Strategy Pattern
		Template Method Pattern
		Visitor Pattern