Implementing Singleton class in .NET

Definition:

“A class which can be instantiated only once is called singleton class”.
The term singleton is derived from the mathematics concept of a singleton. Singleton is set with only one element. E.g.: Set {0} is a singleton.

How to achieve singleton class?

• Mark the constructor as private so that outside the class it’s not possible to create instance of the class.
• Create static/Shared method can be added to the class to create instance of the class and return the reference of the object.

Sample Program:

class SingletonClass
    {
        private static SingletonClass obj;
        public int tempVal
        {
            get; set;
        }
 
        //private constuctor
        private SingletonClass()
        {
        }
 
        public static SingletonClass GetInstance()
        {
            if (obj == null)
            {
                obj = new SingletonClass();                
            }
            return obj;
        }
    }
    class SingletonClassProgram
    {
        public static void Main(string[] args)
        {
            SingletonClass obj1,obj2;
            //obj1=new SingletonClass(); //invlid due to constructore is private. Error as inaccissible due to protection level
             obj1=SingletonClass.GetInstance();
            obj1.tempVal =20;
            obj2=SingletonClass.GetInstance();
 
            Console.WriteLine(" /********* singleton class Example **********/");
            Console.WriteLine("variable value is {0}",obj2.tempVal); //value is 20 because both obj1,obj2 are referring to same object
            Console.Read();
 
        }
    }

Output:

Data Points

• Singleton is a design pattern in software development.
• Single class is like a sealed class