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c#static-constructor
Strider007
Strider007

Reputation: 4975

Public constructor and static constructor

I am reading a code in C# that uses two constructors. One is static and the other is public. What is the difference between these two constructors? And for what we have to use static constructors?

Upvotes: 18

Views: 12970

Answers (4)

Hasan Fathi
Hasan Fathi

Reputation: 6106

Static constructor called only the first instance of the class created but the public constructor called every time that instance of the class is created.

Static Constructor

A constructor declared using a static modifier is a static constructor. A static constructor is used to initialize static data or to perform a particular action that needs to be performed only once in the life cycle of class. A static constructor is the first block of code to execute in class. Static constructor executes one and only one time in the life cycle of class. It is called automatically. The static constructor does not take any parameters. It has no access to specifiers. It is not called directly.

Instance or Public Constructor

Instance constructor is used to initialize instance data. Instance constructor is called every time when the object of the class is created. It is called explicitly. Instance constructor takes parameters. It has access specifiers.

My source: Static Constructor Vs Instance Constructor in C#

Upvotes: 0

Ondrej Slinták
Ondrej Slinták

Reputation: 31970

Static constructor runs just once, before your class is instantiated. It's used if you want something to happen just once. A nice example would be a Bus class (similar to something they explain in MSDN article):

public class Bus
{
    public static int busNo = 0;

    static Bus()
    {
        Console.WriteLine("Woey, it's a new day! Drivers are starting to work.");
    }

    public Bus()
    {
        busNo++;

        Console.WriteLine("Bus #{0} goes from the depot.", busNo);
    }
}


class Program
{
    static void Main(string[] args)
    {
        Bus busOne = new Bus();
        Bus busTwo = new Bus();
    }

    // Output:
    // Woey, it's a new day! Drivers are starting to work.
    // Bus #1 goes from the depot.
    // Bus #2 goes from the depot.
}

Upvotes: 27

Manish Basantani
Manish Basantani

Reputation: 17509

Static Constructor... It is guaranteed to be called "once" througout the life of the application/app Domain. It can contain statements that you want to be executed only once.

Public Constructor... Since we can not add access modifiers to a static constructor, a public constructor means you are talking about an instance constructor. If an instance constructor is public then the outside world can create its instances. Other options are Internal ( can be called from within the library), Private ( from within the class only).

Upvotes: 3

Konrad Rudolph
Konrad Rudolph

Reputation: 546173

static and public are orthogonal concepts (i.e. they don’t have anything to do with each other).

public simply means that users of the class can call that constructor (as opposed to, say, private).

static means that the method (in this case the constructor) belongs not to an instance of a class but to the “class itself”. In particular, a static constructor is called once, automatically, when the class is used for the first time.

Furthermore, a static constructor cannot be made public or private since it cannot be called manually; it’s only called by the .NET runtime itself – so marking it as public wouldn’t be meaningful.

Upvotes: 36

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