Explanation of Decorator Design Pattern

Now let's begin.

First What is Decorator Design Pattern?

Decorator Design Patter is a Structural Design Pattern that will add specifications dynamically to the components and objects without deriving from related class. ıt is a flexible way to adding responsibilities to the components.

Below image you can see the schematic of decorator Design Pattern

Now I want to share an example:

I want you to think an aircraft and the buyer can request some additional specifications and according to requested additional parts the cost will increase.

Below you will my example:

First we will create an interface to derive all of components and decorators here. We will use some same codes in these classes.

IAircraft.cs

namespace DecoratorPattern_Example
{
    interface IAircraft
    {
        void apply_decoration(Aircraft _ac, string decorationType, bool hasOrNot);
    }
}

And then I will create my decorator classes. Here I will send the component what I will decorate. Also when I try to apply any decoration in the target component, I want to specify the decoration type.

DecorateSeats .cs

using System;

namespace DecoratorPattern_Example
{
    class DecorateSeats : IAircraft
    {
        private bool hasExtendenSeats = false;

        public bool hasDecoration
        {
            get { return hasExtendenSeats; }
            set { hasExtendenSeats = value; }
        }

        public void apply_decoration(Aircraft _ac, string decorationType, bool hasOrNot)
        {
            this.hasExtendenSeats = hasOrNot;
            _ac.apply_decoration(_ac, decorationType, hasOrNot);
            Console.WriteLine("Seats decoration Applied Status : " + hasOrNot.ToString());
        }
    }
}

DecorateFuelTank .cs

using System;

namespace DecoratorPattern_Example
{
    class DecorateFuelTank : IAircraft
    {
        private bool hasExtendenFuelTank = false;

        public bool hasDecoration
        {
            get { return hasExtendenFuelTank; }
            set { hasExtendenFuelTank = value; }
        }

        public void apply_decoration(Aircraft _ac, string decorationType, bool hasOrNot)
        {
            this.hasExtendenFuelTank = hasOrNot;
            _ac.apply_decoration(_ac, decorationType, hasOrNot);
            Console.WriteLine("FuelTank decoration Applied Status : " + hasOrNot.ToString());
        }
    }
}

Here is my component class. I will manage everything which related to component here. Also I will derive this class from the interface that I declared above to allow the external decorations from another classes which derived from same class.

Aircraft .cs

using System;

namespace DecoratorPattern_Example
{
    class Aircraft : IAircraft
    {
        public string brand = "";
        public string model = "";
        public int price = 0;
        public bool hasExtendedSeats = false;
        public bool hasExtendedFuelTanks = false;

        public Aircraft(string _brand, string _model, int _price)
        {
            this.brand = _brand;
            this.model = _model;
            this.price = _price;
        }

        public bool hasDecoration
        {
            get { return false; }
            set { }
        }

        public void apply_decoration(Aircraft _ac, string decorationType, bool hasOrNot)
        {
            if (decorationType == "fueltank") this.hasExtendedFuelTanks = hasOrNot;
            else if (decorationType == "seats") this.hasExtendedSeats = hasOrNot;
        }

        public void print_aircraft_information()
        {
            Console.WriteLine("#################################");
            Console.WriteLine("Aircraft Brand : " + this.brand);
            Console.WriteLine("Aircraft model : " + this.model);
            Console.WriteLine("Aircraft price : " + this.price);
            Console.WriteLine("Aircraft has Extended Seats : " + this.hasExtendedSeats.ToString());
            Console.WriteLine("Aircraft has Extended FuelTanks : " + this.hasExtendedFuelTanks.ToString());
            Console.WriteLine("#################################");
        }
    }
}

Lastly, I will declare the component and decorators first. Then ı will make some changes in the target component via my decorator classes. These decorator classes and the component are the same derivative class.

Program.cs

using System;

namespace DecoratorPattern_Example
{
    class Program
    {
        static void Main(string[] args)
        {
            //First declare the Aircraft component
            Aircraft _aircraft = new Aircraft("Boeing", "B777", 295000000);
            //Then declare the decorator classes
            DecorateFuelTank decorateFuelTank = new DecorateFuelTank();
            DecorateSeats decorateSeats = new DecorateSeats();

            //then decorate the status of aircraft and print
            decorateFuelTank.apply_decoration(_aircraft, "fueltank", true);
            decorateSeats.apply_decoration(_aircraft, "seats", false);
            _aircraft.print_aircraft_information();

            Console.WriteLine("---------------------------------------");
            //redecorate it again and print again
            decorateFuelTank.apply_decoration(_aircraft, "fueltank", false);
            decorateSeats.apply_decoration(_aircraft, "seats", true);
            _aircraft.print_aircraft_information();
            Console.ReadLine();
        }
    }
}

Output:

FuelTank decoration Applied Status : True
Seats decoration Applied Status : False
#################################
Aircraft Brand : Boeing
Aircraft model : B777
Aircraft price : 295000000
Aircraft has Extended Seats : False
Aircraft has Extended FuelTanks : True
#################################
---------------------------------------
FuelTank decoration Applied Status : False
Seats decoration Applied Status : True
#################################
Aircraft Brand : Boeing
Aircraft model : B777
Aircraft price : 295000000
Aircraft has Extended Seats : True
Aircraft has Extended FuelTanks : False
#################################

Below image you can see the output of the program:

I hope it is not complicated.

That is all in this article.

Have a good decorating your components.

Burak Hamdi TUFAN.