public class Program

{

    public static void Main()

    {

        var singletonInstance = Singleton.Instance();

    }

}

​

public class Singleton

{

    // static field (to access within static method and keeping single value) 

    // private (to not allow to be changed outside the class)

    // init to null (initial default value)

    private static Singleton theInstance = null;

    // the default constructor created as private and empty

    private Singleton() {}

    // static method only way to access theInstance field

    public static Singleton Instance()

    {

        if (theInstance == null)

        {

            theInstance = new Singleton();

        }

        return theInstance;

    }

}