Singleton Design Pattern

Singleton design pattern allows to create only one instance of the class by providing only one global point to access it.
This can be achieved by:

1. Making the constructor private/protected.
2. Create a static function which returns an instance of the class only after ensuring class has no other instance.

namespace OopConcept
{
    /// 

    /// Class without explicit contructor 
    /// 
    class singleton
    {
        private static singleton singletonInstance = null;

        /// 

        /// To prevent instantiation.
        /// 
        private singleton()
        {

        }
        public static singleton getInstance()
        {
            if (singletonInstance == null)
            {
                singletonInstance = new singleton();
            }
            return singletonInstance;
        }

    }
    /// 

    /// Main Class - 
    /// 
    class MainClass
    {
        public static void Main()
        {
            // Cannot create an instance with 'new' Keyword.
            singleton firstInstance = singleton.getInstance();
            singleton secondInstance = singleton.getInstance();

            if (firstInstance == secondInstance)
            {
                Console.WriteLine("Two instances are same");
                Console.Read();
            }
        }
    }
}