C# Singleton, Static Class And Difference Between Them

A singleton stores common data in only on place. A static class is also used to store single-instance data. We save state between usages. We store caches to improve performance. The object must be initialized only once and shared.

Singleton: when we create a singleton class using singleton design pattern try to write that class in a way that there could be only one instance. Below is the code which show how to create a singleton class

using System

public sealed class Singleton

{

                private static volatile  Singleton _instance;

                private static object syncRoot = new object();

                private Singleton(){}

                public static Singleton Instance

                {

                get

{

if(_instance == null)

                {

Lock(syncRoot)

{
                                if(_instance == null)

                                                {

                                                                _instance = new Singleton();

}

                                                                }

}

                                                return _instance;

}

}

}

Notes:-

1.       This approach ensures that only one instance is created and only when the instance is needed.

2.       The volatile keyword indicates that a field might be modified by multiple threads that are executing at the same time. Fields that are declared volatile are not subject to compiler optimizations that assume access by a single thread. This ensures that the most up-to-date value is present in the field at all times.

3.       This double-check locking approach solves the thread concurrency problems while avoiding an exclusive lock in every call to the Instance property method. It also allows you to delay instantiation until the object is first accessed.

4.       Making this singleton class sealed will avoid any chance of inheriting this class and making further complicated.

Million Dollar Question: -   So what Benefits we get in a singleton class over a static class?

Answer :- Both singleton class and a static classes are used to have only one instance of that class but there are few benefits which singleton class provides over static class.

1.       Singleton class is lazy load means it load only when it’s required. When we ask for the instance from a static class it will check if there is no instance created it will create it and return the instance but static class object are created and loaded when application starts. Which make application starts slow.

2.       You can implement an interface or derive you Singleton Class from a base class but you can't do the same with static class.

3.       You can have non static in singleton class but your static class should have only static members.

4.       You can pass a singleton class as a parameter to a method but the same you can’t do with static class.

5.       In a static class CLR makes sure there is only one instance of static class, but in case of singleton class we need to write in a way we make sure there is only one instance of singleton class.

Conclusion: - Basically speaking, they are meant for different purposes. A static class can be used as a convenient container for sets of methods that just operate on input parameters and do not have to get or set any internal instance fields. A singleton class can be used when you need a class with all the benefit of a normal class and an additional benefit will be that there will be only one instance of this class.