add implementation for singleton

design_patterns/creational_patterns/singleton/singleton.cs

@@ -0,0 +1,44 @@
+using System;
+using System.Threading.Tasks;
+
+namespace designPatterns
+{
+ class Singleton
+ {
+ private static Singleton _singleton;
+
+ private readonly string message;
+
+ private Singleton()
+ {
+ message = $"this instance was created in {DateTime.Now.Hour}:{DateTime.Now.Minute}:{DateTime.Now.Second}:{DateTime.Now.Millisecond}";
+ }
+
+ public static Singleton GetInstance()
+ {
+ if (_singleton is null)
+ _singleton = new Singleton();
+ return _singleton;
+ }
+
+ public override string ToString()
+ {
+ return message;
+ }
+ }
+ class Program
+ {
+ static void Main(string[] args)
+ {
+ Singleton singleton1 = Singleton.GetInstance();
+ Console.WriteLine("get an instance of singleton class");
+ Console.WriteLine("singleton1=>"+singleton1);
+ Console.WriteLine("wait for 1 second");
+ Task.Delay(1000).Wait();
+ Console.WriteLine("trying to get another instance of it");
+ Singleton singleton2 = Singleton.GetInstance();
+ Console.WriteLine("singleton2=>"+singleton2);
+ }
+ }
+
+}