public static DesignPatterns ObjectOfClass()
 {
     if (objectOfClass == null)
     {
         objectOfClass = new DesignPatterns();
     }
     return objectOfClass;
 }
        static void Main(string[] args)
        {
            var input = "";

            while (input != "exit")
            {
                Console.WriteLine("Welcome to Design Pattern Examples!!");
                Console.WriteLine("0 - exit");
                Console.WriteLine("1 - Factory Method");
                Console.WriteLine("2 - Singleton");
                Console.WriteLine("3 - Dependency Injection");
                Console.WriteLine("4 - Builder");
                input = Console.ReadLine();

                switch (input)
                {
                case "0":
                    Environment.Exit(0);
                    break;

                case "1":
                    DesignPatterns.FactoryMethod();
                    break;

                case "2":
                    DesignPatterns.Singleton();
                    break;

                case "3":
                    DesignPatterns.DependencyInjection();
                    break;

                case "4":
                    DesignPatterns.Builder();
                    break;
                }

                Console.WriteLine();
            }
        }