Design Pattern For Beginners - Part-1: Singleton Design Pattern

Here is some sample output.

Ok, you may think, Sourav!! We are not creating any object in the above example, but in the introduction, why did you say we will create a single object and share it across threads? Yes, we will get to that in the folloing example but believe me, it's also a design style of a singleton pattern. Ultimately, we are sharing a single c ass across various threads (though we did not implement any multi-threading concept). Oh! Are you worried about deadlock problems? Ok, let's see the following example.

how to Create a single instance and share it across threads?

In this example, we will implement a singleton class so that only one instance of that class is possible, and if the second request comes, then it will return the previously created object only. Have a look at the following code.

using System;  
using System.Collections;  
using System.Data.SqlClient;  
namespace Test1  
{  
    public sealed class singleTon  
    {  
        public Int32 Data = 0;  
        private static singleTon instance;  
        private static object syncRoot = new Object(); //For locking mechanism  
        private singleTon() { } //Private constructor  
        public static singleTon Instance //Property  
        {  
            get  
            {  
                if (instance == null)  
                {  
                    lock (syncRoot)  
                    {  
                        if (instance == null)  
                            instance = new singleTon();  
                    }  
                }  
                return instance;  
            }  
        }  
    }  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            //singletone design pattern  
            singleTon s = singleTon.Instance;  
            s.Data = 100;  
            Console.WriteLine("Data of S object : " + s.Data);  
            singleTon s1 = singleTon.Instance;  
            Console.WriteLine("Data of S1 object : " + s.Data);  
            Console.ReadLine();  
        }  
    }  
}

He e we have defined a member called instance within the singleton class. And within the class property (yes, it's also an Instance, but don't be confused), we are checking whether the instance is null using a condition in an if statement. If it is null, then no instance is crated of this class, if it is not, then an instance has already been created, and it's time to return the previously created instance.

Here is a sample output of this example.

Now, we will analyze the Main() function here. Have a look at the following code.

singleTon s = singleTon.Instance;  //First instance  
s.Data = 100; //Data of first instance           
Console.WriteLine("Data of S object : " + s.Data);  
singleTon s1 = singleTon.Instance;  //Again request and return old instance  
Console.WriteLine("Data of S1 object : " + s.Data);  //Show data of old instance  
Console.ReadLine();

In the first two lines, we create the first instance of the singleton class and set the data value. Now in the fourth line, we are again requesting a new object of the singleton class, but there is no chance of getting a new one (since this is our main target), and from the property, the old one is returned. Yes, that's why in the first object, we have set Data=100, and it has been reflected in the second instance, proving that no new object has been created.

Conclusion

It's time to summarize my article. By habit, in my previous "Best performance of C# code" series of articles, I wrote something for my dear respected Sam (Who is an enthusiastic editor and critic of the C# article). Sam is waiting for your comment, and let's improve my way of learning. Make me more serious before writing t e following code sample for my next article.

Continue Reading

• Design Pattern For Beginners - Part 2: Factory Design Pattern
• Design Pattern For Beginners - Part 3: Prototype Design Pattern
• Design Pattern For Beginners - Part 4: Decorator Design Pattern
• Design Pattern For Beginners - Part 5: Composite Design Pattern
• Design Pattern For Beginners - Part 6: Adaptor Design Pattern
• Design Pattern For Beginners - Part 7: Bridge Design Pattern
• Design Pattern For Beginners - Part 8: memento Design Pattern
• Design Pattern for Beginners - Part-9: Strategy Design Pattern
• Design Pattern for Beginners - Part-10: Observer Design Pattern
• Design Pattern For Beginners - Part 11: Implement Decouple Classes in Application