In .Net does static class internally create one object or does it not create any object at all. As per Microsoft docs
As is the case with all class types, the type information for a static class is loaded by the .NET Framework common language runtime (CLR) when the program that references the class is loaded. The program cannot specify exactly when the class is loaded. However, it is guaranteed to be loaded and to have its fields initialized and its static constructor called before the class is referenced for the first time in your program. A static constructor is only called one time, and a static class remains in memory for the lifetime of the application domain in which your program resides.
Can we say an object is created implicitly here.? I'm sure that simply writing static class won't create memory for it until static class or any of its members are referenced some where in code. Correct me if i'am wrong.
If I understood your question correctly, you are interested if the static class object is initialized if you don't call it from anywhere in the code.
So, I just created simple console application with static class, and put some Console.WriteLine commands in the constructor like this:
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
}
}
static class SomeClass
{
static SomeClass()
{
Console.WriteLine(GetId(1));
Console.WriteLine(GetId(2));
}
public static string GetId(int Id) { return Id.ToString(); }
}
I got the following output:
Hello World!
Then I run the program with the access to the static class:
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
Console.WriteLine(SomeClass.GetId(3));
}
}
static class SomeClass
{
static SomeClass()
{
Console.WriteLine(GetId(1));
Console.WriteLine(GetId(2));
}
public static string GetId(int Id) { return Id.ToString(); }
}
And here, my console output was:
Hello World!
1
2
3
Which means that if you don't call the class inside your program, it is not being initialized and the object is not created accordingly.
But if you access the class, the object is created before it's accessed first time in the code, that means that constructor creates it when it's first called, without separate initialization, like: var _someClass = new SomeClass();, it is created before first access, and is created only once during the lifetime of your program, and no matter how much times you call it in your code, after first initialization, the instance lives until your software is running, as no matter how much times or where I would use functions or properties from this SomeClass across the program, I would be reusing the same instance, and if you don't call the class within your code, instance is not created at all, and that's what Microsoft docs refer to I suppose.
Related
This question already has answers here:
Instantiating the class that contains static void Main()
(8 answers)
c# : console application - static methods
(5 answers)
Closed 1 year ago.
I am getting the following Warning in Visual Studio 2019, after creating a new ASP.NET Core 3 project:
Warning CA1052
Type 'Program' is a static holder type but is neither static nor NotInheritable
public class Program
{
public static void Main(string[] args)
{
// ...
}
public static IHostBuilder CreateHostBuilder(string[] args) =>
// ...
}
vs
public static class Program
{
public static void Main(string[] args)
{
// ...
}
public static IHostBuilder CreateHostBuilder(string[] args) =>
// ...
}
Should I add the static modifier? Why / Why not? Pro's and Cons'?
Edit: This is a ASP.NET Core 3 API
In more basic terms the message could be imagined to say:
Your class 'Program' only seems to contain methods that are declared as static and as a result it can not participate in an inheritance hierarchy. Declare it as static (or sealed if you're targeting an ancient version of .net that doesn't support static classes) to more accurately reflect what its design sentiment is
It's a recommendation, to mark your class as static because it only contains static stuff. This will prevent anyone making the mistake of trying to inherit from it and thinking they can then do something useful inheritance-wise with the inherited version
Microsoft don't mark it as static for you because there's nothing special about Program per se; you could put non static methods in it, or your could put your static void Main in another class, like Person, that IS instantiable.
class Person{
public string Name {get;set;}
static void Main(){
Person p = new Person();
p.Name = Console.ReadLine();
}
}
This would work fine; a class does not have to be static to host the application entry point and in this case the class couldn't be static because it has non static members. It can be (and is, in the main) instantiated in the main. It's not called Program; there isn't a class called Program anywhere and this tiny app will still run (doesn't do much..)
In your case, either do as recommended and add a static modifier to your class, because it will make your program that bit more robustly engineered, or add an instance member if you can think of a valid reason for instantiating Program, or ignore the message and carry on with your non static class that contains only static methods - it'll still work
I have many classes in an assembly that I can't or don't want to modify. At some point of runtime, I want to know which of them have already been "initialized": static initializer (= static constructor) has run.
Is there a way to do it with reflection or something else?
For information, not every class in an assembly is initialized when the assembly is loaded. This can be easily observed with this piece of code:
public static class Foo
{
static Foo() { MainClass.Value = "Something"; }
public static void DoSomething() { Thread.Sleep(100); }
}
public static class MainClass
{
public static string Value = "Nothing";
public static void Main()
{
Console.WriteLine(Value);
Foo.DoSomething();
Console.WriteLine(Value);
}
}
Displays:
Nothing
Something
As said HimBromBeere, and as confirmed in this article,
A static constructor is called automatically to initialize the class before the first instance is created or any static members are referenced.
So you need to use your class once, a property, a method, whatever, to initialize it... You have no control on it, you can't call it programatically and, if you want to know if the static constructor has been used, you'll use the class, so it could be called at this point...
As said Rango, you can use a flag in your constructor, if you really absolutly need to know...
Consider this example code:
public class A<T>
{
public static T TheT { get; set; }
}
public class B : A<string>
{
static B() {
TheT = "Test";
}
}
public class Program {
public static void Main(String[] args) {
Console.WriteLine(B.TheT);
}
}
Here B.TheT is null. However, changing the Main method like this:
public static void Main() {
new B();
Console.WriteLine(B.TheT);
}
B.TheT is "Test", as expected. I can understand that this forces the static constructor to run, but why does this not happen for the first case?
I tried reading the spec, and this caught my attention (§10.12):
[...] The execution of a static constructor is triggered by the first of the
following events to occur within an application domain:
• [...]
• Any of the static members of the class type are referenced.
My interpretation of this is that since TheT is not a member of B, the static constructor of B is not forced to be run. Is this correct?
If that is correct, how would I best let B specify how to initialize TheT?
A.TheT is "Test", as expected. I can understand that this forces the static constructor to run, but why does this not happen for the first case?
Basically, you haven't really referenced B. If you look in the IL, I think you'll find that your code was actually equivalent to:
public static void Main(String[] args) {
Console.WriteLine(A<string>.TheT);
}
The compiler worked out that that's really the member you meant, even though you wrote B.TheT.
If that is correct, how would I best let A specify how to initialize TheT?
I would try to avoid doing this to start with, to be honest... but you could always just add a static method to B:
public static void Initialize() {
// Type initializer will be executed now.
}
Static constructor is called before the first access or at the latest when the first access is made. I.e you know it has been called when first access is made but not how long before. However, if no access is made it won't be called. So you cannot control when only if it s called.
As per MSDN reference
A static constructor is used to initialize any static data, or to perform a particular action that needs performed once only. It is called automatically before the first instance is created or any static members are referenced.
In second case called static contructor and it will call the actual types' static contructor, and not that one of derived one. So in your case it calls the static ctor of the A<T> =>A<string> and not of A.
To prove this behaviour just do the following:
public class Base {
static Base() {
"Base static".Dump();
}
}
public class Derived : Base {
static Derived() {
"Derived static".Dump();
}
public static string temp = "Hello";
}
and call
Derived.temp.Dump();
You will get:
Derived static
Hello
This is what you actually do in your code, you acess derived type A<string> and it's default static ctor is called.
I stumbled upon a problem where i need an instance of the class inside its static constructor. I believed it was not possible to do it so i tried the following:
class Program
{
static void Main(string[] args)
{
Console.WriteLine(Foo.someString);
Console.ReadLine();
}
}
class Foo
{
public static readonly string someString;
static Foo()
{
someString = new Foo().CreateString();
}
private string CreateString()
{
return "some text";
}
}
To my surprise, it works - the output is "some text". I believed the static constructor must run and complete before instances of the class can be created. This answer shows that this is not necessarily the case. Does this mean that static and instance constructors are independent of each other? And finally, is it safe to do this (create instances in static constructor)?
p.s. Let's ignore the fact that this can be avoided by using a different approach.
All that the specification says is that the static constructor will be called before any instance of the class is created. But it doesn't state anything about the fact that this constructor must finish:
A static constructor is used to initialize any static data, or to
perform a particular action that needs to be performed once only. It
is called automatically before the first instance is created or any
static members are referenced.
You could perfectly fine create instances of the class inside the static constructor and this is safe.
It is safe as it will be called only once.
Static constructor called automatically before the first instance is created or any static members are referenced any static fields are referenced. Hence when your application ran and you accessed Foo, the static constructor was executed and your string was initialized.
Is it safe ? : As such there is no harm in doing this. It is just they are executed only once.
For information on this read Static Classes and Static Class Members on MSDN
why in C#, console application, in "program" class , which is default, all methods have to be static along with
static void Main(string[] args)
Member functions don't have to be static; but if they are not static, that requires you to instantiate a Program object in order to call a member method.
With static methods:
public class Program
{
public static void Main()
{
System.Console.WriteLine(Program.Foo());
}
public static string Foo()
{
return "Foo";
}
}
Without static methods (in other words, requiring you to instantiate Program):
public class Program
{
public static void Main()
{
System.Console.WriteLine(new Program().Foo());
}
public string Foo() // notice this is NOT static anymore
{
return "Foo";
}
}
Main must be static because otherwise you'd have to tell the compiler how to instantiate the Program class, which may or may not be a trivial task.
You can write non static methods too, just you should use like this
static void Main(string[] args)
{
Program p = new Program();
p.NonStaticMethod();
}
The only requirement for C# application is that the executable assembly should have one static main method in any class in the assembly!
The Main method is static because it's the code entry point to the assembly. There is no instance of any object at first, only the class template loaded in memory and its static members including the Main entry point static method. Main is predefined by the C# compiler to be the entry point.
A static method can only call other static methods (unless there is an instance handle of something composited for use). This is why the Main method calls other static methods and why you get a compile error if you try to call a non-static (instance) method.
However, if you create an instance of any class, even of the Program class itself, then you start creating objects in your application on the heap area of memory. You can then start calling their instance members.
Not all methods have to be static, you can add instance methods and also create an instance of your Program class.
But for Main it has to be static beacause it's the entry point of your application and nobody is going to create an instance and call it.
So, technically correct answers are above :)
I should point out that generally you don't want to go in the direction of all static methods. Create an object, like windows form, a controller for it and go towards object-oriented code instead on procedural.