FACADE DESIGN PATTERN

According to GoF’s definition, facade pattern is :

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.

A real world example :

In this example we need to start computer. Computer class acts as facade which encapsulates other complex classes represented by: HardDrive class, Memory class and CPU class. Each of this classes has operations which must be performed when Start() method of Computer class is called.

public class Computer
    {
        private readonly CPU _cpu;
        private readonly HardDrive _hardDrive;
        private readonly Memory _memory;
 
        private const long BootAddress = 1;
        private const long BootSector = 1;
        private const int SectorSize = 10;
 
        public Computer()
        {
            _cpu = new CPU();
            _hardDrive = new HardDrive();
            _memory = new Memory();
        }
 
        public void Start()
        {
            _cpu.Freeze();
            _memory.Load(BootAddress, _hardDrive.Read(BootSector, SectorSize));
            _cpu.Jump(BootAddress);
            _cpu.Execute();
        }
    }
 
    public class CPU
    {
        public void Freeze()
        {
            Console.WriteLine("CPU is frozen");
        }
 
        public void Jump(long position)
        {
            Console.WriteLine("Jumping to position: {0}", position);
        }
 
        public void Execute()
        {
            Console.WriteLine("Executing...");
        }
    }
 
    public class HardDrive
    {
        
            public byte[] Read(long lba, int size)
            {
                var bytes = new byte[size];
                var random = new Random();
                random.NextBytes(bytes);
                return bytes;
            }
    }
 
    public class Memory
    {
        public void Load(long position, byte[] data)
        {
            Console.WriteLine("Loading data: ");
            foreach (var b in data)
            {
                Console.Write(b+ " ");
                Thread.Sleep(1000);
            }
 
            Console.WriteLine("\nLoading compleded");
        }
    }
 
    class Program
    {
        static void Main()
        {
            var computer = new Computer();
            computer.Start();
        }
    }

Real Example Using Car  -

 
class CarModel
{
    public void SetModel()
    {
        Console.WriteLine(" CarModel - SetModel");
    }
}
class CarEngine
{
    public void SetEngine()
    {
        Console.WriteLine(" CarEngine - SetEngine");
    }
}
class CarBody
{
    public void SetBody()
    {
        Console.WriteLine(" CarBody - SetBody");
    }
}
class CarAccessories
{
    public void SetAccessories()
    {
        Console.WriteLine(" CarAccessories - SetAccessories");
    }
}
public class CarFacade
{
    CarModel model;
    CarEngine engine;
    CarBody body;
    CarAccessories accessories;

    public CarFacade()
    {
        model = new CarModel();
        engine = new CarEngine();
        body = new CarBody();
        accessories = new CarAccessories();
    }

    public void CreateCompleteCar()
    {
        Console.WriteLine("******** Creating a Car **********\n");
        model.SetModel();
        engine.SetEngine();
        body.SetBody();
        accessories.SetAccessories();

        Console.WriteLine("\n******** Car creation complete **********");
    }
}
class Program
{
    static void Main(string[] args)
    {
        CarFacade facade = new CarFacade();
        facade.CreateCompleteCar();
        Console.ReadKey();
    }
}