C# - Static Constructor in C#.NET with Example

Here I will explain what is static constructor in c# with example. Static constructor in c# is used to create static fields of the class and to write the code that needs to be executed only once. 

Description:

In previous posts I explained use of virtual, override and new keyword with examples in c# method overloading and overriding, delegates example in c#, sealed class in c#, using statement in c#, OOPS examples in c# and many articles relating tointerview questions in c#, asp.net, SQL server, JavaScript, jQuery. Now I will explain static constructor in c#.net with example.

Constructor is a special method of a class which will invoke automatically whenever instance or object of class is created. Constructors are responsible for object initialization and memory allocation of its class. If we create any class without constructor, the compiler will automatically create one default constructor for that class. There is always at least one constructor in every class. If you want to know more about constructors check this article constructors in c#.

Static Constructor

When we declared constructor as static it will be invoked only once for any number of instances of the class and it’s during the creation of first instance of the class or the first reference to a static member in the class. Static constructor is used to initialize static fields of the class and to write the code that needs to be executed only once.

using System; namespace ConsoleApplication3 { class Sample { public string param1, param2; static Sample() { Console.WriteLine("Static Constructor"); } public Sample() { param1 = "Sample"; param2 = "Instance Constructor"; } } class Program { static void Main(string[] args) { // Here Both Static and instance constructors are invoked for first instance Sample obj=new Sample(); Console.WriteLine(obj.param1 + " " + obj.param2); // Here only instance constructor will be invoked Sample obj1 = new Sample(); Console.WriteLine(obj1.param1 +" " + obj1.param2); Console.ReadLine(); } } }

When we run above program we will get output like as shown below

Output

Static Constructor Sample Instance Constructor Sample Instance Constructor

Importance points of static constructor

-      Static constructor will not accept any parameters because it is automatically called by CLR.

-      Static constructor will not have any access modifiers.

-      Static constructor will execute automatically whenever we create first instance of class

-      Only one static constructor will allowed.

I hope it helps to know about static constructor. If you want to know more about constructors check this article constructors in c#.