Programming - Facade Structural Design Pattern

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.

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

Facadeand
and
- knows which subsystem classes are responsible for a request.
- delegates client requests to appropriate subsystem objects.
Subsystem classesand
and and
- implement subsystem functionality.
- handle work assigned by the Facade object.
- have no knowledge of the facade and keep no reference to it.

// Facade pattern -- Structural example

                using
              
              System;

               namespace

DoFactory.GangOfFour.Facade.Structural
{

// Mainapp test application

class MainApp
{
public static void Main()
{
Facade facade = new Facade();

facade.MethodA();
facade.MethodB();

// Wait for user
Console.Read();
}
}

// "Subsystem ClassA"

class SubSystemOne
{
public void MethodOne()
{
Console.WriteLine(" SubSystemOne Method");
}
}

// Subsystem ClassB"

class SubSystemTwo
{
public void MethodTwo()
{
Console.WriteLine(" SubSystemTwo Method");
}
}

// Subsystem ClassC"

class SubSystemThree
{
public void MethodThree()
{
Console.WriteLine(" SubSystemThree Method");
}
}

// Subsystem ClassD"

class SubSystemFour
{
public void MethodFour()
{
Console.WriteLine(" SubSystemFour Method");
}
}

// "Facade"

class Facade
{
SubSystemOne one;
SubSystemTwo two;
SubSystemThree three;
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();
}
}
}

and

Output expected:

              MethodA() ----

               SubSystemOne Method

               SubSystemTwo Method

               SubSystemFour Method

               MethodB() ----

               SubSystemTwo Method

               SubSystemThree Method