Singleton Design Pattern

Singleton define as a class of which only a single instance can exist by

This pattern has no logical diagram because it is not as complicated.

You can see in the sample below there is only a simple class, Singleton. This class defines an Instance operation that lets clients access its unique instance. Instance is a class operation and responsible for creating and maintaining its own unique instance.

The theory of this is simple. The data members of the Singleton class must be static and the member functions of the Singleton class must also be static.


using System;


namespace ConAppSingleton


    class MainApp


        static void Main()


            // Constructor is protected — cannot use new

            Singleton s1 = Singleton.Instance();

            Singleton s2 = Singleton.Instance();


            // Test for same instance

            if (s1 == s2)


                Console.WriteLine(“Objects are the same instance”);



            // Wait for user





    class Singleton


        private static Singleton _instance;


        // Constructor is ‘protected’

        protected Singleton()




        public static Singleton Instance()


            // Uses lazy initialization.

            // Note: this is not thread safe.

            if (_instance == null)


                _instance = new Singleton();



            return _instance;




You can also download a single solution from The sample file name is My MSN ID is


About chanmingman

Since March 2011 Microsoft Live Spaces migrated to Wordpress ( till now, I have is over 1 million viewers. This blog is about more than 50% telling you how to resolve error messages, especial for Microsoft products. The blog also has a lot of guidance teaching you how to get stated certain Microsoft technologies. The blog also uses as a help to keep my memory. The blog is never meant to give people consulting services or silver bullet solutions. It is a contribution to the community. Thanks for your support over the years. Ming Man is Microsoft MVP since year 2006. He is a software development manager for a multinational company. With 25 years of experience in the IT field, he has developed system using Clipper, COBOL, VB5, VB6, VB.NET, Java and C #. He has been using Visual Studio (.NET) since the Beta back in year 2000. He and the team have developed many projects using .NET platform such as SCM, and HR based applications. He is familiar with the N-Tier design of business application and is also an expert with database experience in MS SQL, Oracle and AS 400.
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