Singleton

[sunshin5]

public sealed class Singleton4
{
    private Singleton4()
    {
        Console.WriteLine("An instance of Singleton4 is created.");
    }

    public static void Print()
    {
        Console.WriteLine("Singleton4 Print");
    }

    private static Singleton4 instance = new Singleton4();
    public static Singleton4 Instance
    {
        get
        {
            return instance;
        }
    }
}

public sealed class Singleton5
{
    Singleton5()
    {
        Console.WriteLine("An instance of Singleton5 is created.");
    }

    public static void Print()
    {
        Console.WriteLine("Singleton5 Print");
    }

    public static Singleton5 Instance
    {
        get
        {
            return Nested.instance;
        }
    }

    class Nested
    {
        static Nested()
        {
        }

        internal static readonly Singleton5 instance = new Singleton5();
    }
}

class Program
{
    static void Main(string[] args)
    {
        // 也会打印An instance of Singleton4 is created.
        Singleton4.Print();

        // 不会打印An instance of Singleton5 is created.
        Singleton5.Print();
        Console.WriteLine("Finished!!!");
    }
}

实测Netcore下Singleton4也不会打印An instance of Singleton4 is created；但是NetFrameWork也会打印An instance of Singleton4 is created.