Singleton Design Pattern in C#

Ensures a class has only one instance and provide a global point of access to it.

This structural code demonstrates the Singleton pattern which assures only a single instance (the singleton) of the class can be created.

using System;

  class MainApp
  {
 
    static void Main()
    {
      // Constructor is protected -- cannot use new 
      Singleton s1 = Singleton.Instance();
      Singleton s2 = Singleton.Instance();

      if (s1 == s2)
      {
        Console.WriteLine("Objects are the same instance");
      }

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

  // "Singleton" 
  class Singleton
  {
    private static Singleton instance;

    // Note: Constructor is 'protected' 
    protected Singleton() 
    {
    }

    public static Singleton Instance()
    {
      // Use 'Lazy initialization' 
      if (instance == null)
      {
        instance = new Singleton();
      }

      return instance;
    }
  }
}