Facade Design Pattern

Definition

Provide a unified interface to a set of interfaces in a subsystem. Façade defines a higher-level interface that makes the subsystem easier to use.

UML class diagram

 

Participants

    The classes and/or objects participating in this pattern are:

• Facade   (MortgageApplication)
  • knows which subsystem classes are responsible for a request.
  • delegates client requests to appropriate subsystem objects.
• Subsystem classes   (Bank, Credit, Loan)
  • implement subsystem functionality.
  • handle work assigned by the Facade object.
  • have no knowledge of the facade and keep no reference to it.

 Sample Code in C#

// Facade pattern -- Structural example

using System; namespace DoFactory.GangOfFour.Facade.Structural {   /// <summary>   /// MainApp startup class for Structural   /// Facade Design Pattern.   /// </summary>   class MainApp   {     /// <summary>     /// Entry point into console application.     /// </summary>     public static void Main()     {       Facade facade = new Facade();       facade.MethodA();       facade.MethodB();       // Wait for user       Console.ReadKey();     }   }   /// <summary>   /// The 'Subsystem ClassA' class   /// </summary>   class SubSystemOne   {     public void MethodOne()     {       Console.WriteLine(" SubSystemOne Method");     }   }   /// <summary>   /// The 'Subsystem ClassB' class   /// </summary>   class SubSystemTwo   {     public void MethodTwo()     {       Console.WriteLine(" SubSystemTwo Method");     }   }   /// <summary>   /// The 'Subsystem ClassC' class   /// </summary>   class SubSystemThree   {     public void MethodThree()     {       Console.WriteLine(" SubSystemThree Method");     }   }   /// <summary>   /// The 'Subsystem ClassD' class   /// </summary>   class SubSystemFour   {     public void MethodFour()     {       Console.WriteLine(" SubSystemFour Method");     }   }   /// <summary>   /// The 'Facade' class   /// </summary>   class Facade   {     private SubSystemOne _one;     private SubSystemTwo _two;     private SubSystemThree _three;     private SubSystemFour _four;     public Facade()     {       _one = new SubSystemOne();       _two = new SubSystemTwo();       _three = new SubSystemThree();       _four = new SubSystemFour();     }     public void MethodA()     {       Console.WriteLine("\nMethodA() ---- ");       _one.MethodOne();       _two.MethodTwo();       _four.MethodFour();     }     public void MethodB()     {       Console.WriteLine("\nMethodB() ---- ");       _two.MethodTwo();       _three.MethodThree();     }   } }

Output MethodA() ---- SubSystemOne Method SubSystemTwo Method SubSystemFour Method MethodB() ---- SubSystemTwo Method SubSystemThree Method

Reference :- http://www.dofactory.com