singleton classic C# example

Program.cs

namespace SingletonExample
{
    class Program
    {
        static void Main()
        {
            Singleton obj = Singleton.GetInstance();

            Console.WriteLine(obj.GetValue());
            obj.SetValue(75);
            Console.WriteLine(obj.GetValue());
        }
    }

    public class Singleton
    {
        private static Singleton? instance = null;
        private int value;

        private Singleton()
        {
            value = 50;
        }

        public static Singleton GetInstance()
        {
            if (instance == null)
            {
                instance = new Singleton();
            }
            return instance;
        }

        public int GetValue()
        {
            return value;
        }

        public void SetValue(int value)
        {
            this.value = value;
        }
    }
}