I'm currently reading this book online:
http://www.angelfire.com/theforce/chewy0/csharp/Thinking_in_C-Sharp_.pdf
On page 23 (38 of the PDF document) it states that internal classes cannot be accessed from classes within external namespaces.
However, in the online Microsoft documentation it states that internal classes are only accessible from the same assembly.
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/internal
From my understanding, an assembly can contain classes from multiple namespaces.
Would this not mean from the Microsoft documentation that internal classes could be accessed across different namespaces?
Or is it true to say that internal classes are private within both of their respected assemblies and namespaces?
So this is the excerpt, right?
Java uses five explicit keywords to set the boundaries in a class: public,
private, protected, internal, and protected internal. Their use and
meaning are quite straightforward. These access specifiers determine who
can use the definitions that follow. public means the following
definitions are available to everyone. The private keyword, on the other
hand, means that no one can access those definitions except you, the
creator of the type, inside member functions of that type. private is a
brick wall between you and the client programmer. If someone tries to
access a private member, they’ll get a compile-time error. protected
acts like private, with the exception that an inheriting class has access to
protected members, but not private members. Inheritance will be
introduced shortly. internal is often called “friendly”–the definition can
be accessed by other classes in the same namespace as if it were public,
but is not accessible to classes in different namespaces. Namespaces will
be discussed in depth in chapter #ref# [sic]. protected internal allows
access by classes within the same namespace (as with internal) or by
inheriting classes (as with protected) even if the inheriting classes are
not within the same namespace.
C#’s default access, which comes into play if you don’t use one of the
aforementioned specifiers, is internal
The author is probably conflating Java's internal with c#'s internal.
They are slightly different, because Java does not have assemblies; it has packages, which organize classes into namespaces.
In c#, namespace has absolutely no relationship with accessibility modifiers. Only classes within the same assembly can access an internal type or member, unless you use the InternalsVisibleTo attribute. Namespace doesn't matter.
Well, the easiest way to answer this was to test it-
So I've made 2 namespaces within 1 assembly, and accessed an internal variable.
Short answer- the Microsoft documentation is correct- it's possible to access an internal variable within the same assembly, even when you have 2 different namesapces.
Here's the code:
namespace ConsoleApplication1
{
class Class1
{
internal string thing;
public Class1()
{
thing = "original data";
}
}
}
namespace ConsoleApplication2
{
class Class2
{
public ConsoleApplication1.Class1 class1= new ConsoleApplication1.Class1();
public Class2()
{
class1.thing = "other namespace modification";
}
}
}
When calling Class2 constructor, the modified data was displayed.
var class2 = new ConsoleApplication2.Class2();
Console.WriteLine(class2.class1.thing);
Result:
"other namespace modification"
Hope this helps :)
I have noticed for high demand in my projects for objects such as textboxes or buttons public.
Is there any problems by setting them public?
What does public, private, static really mean?
Access Modifiers (C# Programming Guide)
public
The type or member can be accessed by any other code in the same
assembly or another assembly that references it.
private
The type or member can be accessed only by code in the same class or
struct.
protected
The type or member can be accessed only by code in the same class or
struct, or in a class that is derived from that class.
internal
The type or member can be accessed by any code in the same assembly,
but not from another assembly.
protected internal
The type or member can be accessed by any code in the assembly in
which it is declared, or from within a derived class in another
assembly. Access from another assembly must take place within a class
declaration that derives from the class in which the protected
internal element is declared, and it must take place through an
instance of the derived class type.
There is no security risk as far as I know. But there may be better alternative approach to design your program
public, private, etc are called access modifiers and determine the rules for which other code are allowed to access each member.
There is no technical problem of setting controls as public. But I would not recommend it. Having everything public is a good recipe for creating spaghetti code.
Keep all access to controls within your form and expose only a small set of public methods with a simple interface for external actors to access data and operations on the form.
You should not, for a clean design.
You should in reality put the logic of your application outside forms!
However, if you want to keep logic inside forms, you should at least expose them with public properties and methods, without giving direct access to form controls.
For example you can provide things like a method "EnableSave" or "QuitApplication" or "UpdateState".
Public, private and static deal with scope and what can talk to the objects / methods
Public -> Other classes can create an instance of your class (assuming the class is public) and call this object / method directly
Private -> Other classes can create an instance of your class (assuming the class is public) but can NOT access this object / method
Static -> Other classes can directly access this object / method (assuming class is public and method is public static) such as: YourClassName.ObjectOrMethod without having to create an instance of YourClassName
The best access modifier to give to a gui component when you want to access it directly is :internal (that is the default in VB.NET for example).
However you shouldn't give a public or internal modifier on a GUI control and you shouldn't access it directly, because the presentation layer and business logic layer should be kept separated in a well designed architecture ...
I want to create a class outside a namespace so that its default access modifier is 'PRIVATE'. I am doing like this:
namespace KnowStructs
{
class Clas1 {}
}
class MyClass {}
But still my class 'MyClass' is referred as Internal when I look in Reflector.
Can anyone help me out.
From Accessibility Levels:
Top-level types, which are not nested in other types, can only have internal or public accessibility. The default accessibility for these types is internal.
and:
Access modifiers are not allowed on namespaces. Namespaces have no access restrictions.
and for private:
Private members are accessible only within the body of the class or the struct in which they are declared
That is, the private keyword is explicitly defined in terms of a containing class or struct.
So whatever you're trying to do, I don't understand it. How could a top level private type possibly be useful? No other code would be able to reference it (in any way, even if it had e.g. static factory methods).
If a private class is allowed that is not a nested type then what would that mean? If it is more restrictive than internal then how would you use it or create an instance. Any use case will require it to be internal at a minimum. I would like to see how you intend to use it.
It simply makes no logical sense.
Whereas having a private nested class scopes itself to the parent containing class. If it were internal then you still will be able to make an instance within the assembly.
So for classes having no modifier is internal by default for non nested types and private for nested types as .Net always applies the most restrictive access when no modifier is specified.
You can make the class internal, if you only want to be accessible by classes in your namespace
I create a sample class in vs2010.
Through Class View, I see the default access modifier for Main is internal.
I also see some people say that the default access modifier for Main is "implicitly private".
Visual Studio 2010 automatically defines a program’s Main() method as implicitly private. Doing so ensures other applications cannot
directly invoke the entry point of another.
I know there are differences between internal and private. So which one is correct?
If your code appears like this:
static void Main()
then that's a private method. (The static part is orthogonal to accessibility, but is necessary to be an entry point.) In general, the default accessibility of any member is the most private accessibility that you could declare it. So for methods in a class or a struct, that's private. For top-level (non-nested) types it's internal. For any member declared in a class/struct, it's private1. For interface and enum members, it's public.
It's hard to understand exactly what you're seeing via Class View without seeing either your code or a screenshot of Class View, but the default accessibility for a method is definitely private. That's true regardless of whether it's the Main method or not.
1 Explicit interface implementation is a bit odd here, as it's neither private nor public; it's simply not accessible through the type, only through the interface.
Although you tagged your question c#, let me say that the access modifiers for the default Program.Main generated by VS2010 actually depends on the project template, on these differ for each language. I quickly tried the following:
In a VB.NET console project, the Program module (static class) is Friend (i.e. internal in C#) and the Main static method is Public.
In a C# console project, Program is internal, and Main is private.
That is, a C# project will simply use the default access modifiers (internal for classes, private for methods).
You can't see the default access modifier for a member in the class browser, you can see the actual access modifier.
The default access modifiers for classes at the namespace level is internal, whereas the default access modifier for class members (including nested classes) is private. There's no special case for the Main() function. If there's no access modifier before it (a la Jon Skeet's example), then it's private. If there is one, then that's what it is.
Both, the default class modifier is internal. The main method is a method and is private. In general, classes without a modifier are internal, class-members (such as methods and fields) without a declaration are private.
Private members are accessible only within the body of the class in which they are declared.
Internal types or members are accessible only within files in the same assembly
Internal 'is like' public but only for all elements of the same assembly. Class1 of assembly1 cannot 'see' or access any internal element of assembly2.
By Default the access specifier for Main() in C# is private.
This is what I got when I saw the MSIL(IL) code in ILDASM.
You can see that Main() is private.
All my college years I have been using public, and would like to know the difference between public, private, and protected?
Also what does static do as opposed to having nothing?
Access modifiers
From learn.microsoft.com:
public
The type or member can be accessed by any other code in the same assembly or another assembly that references it.
private
The type or member can only be accessed by code in the same class or struct.
protected
The type or member can only be accessed by code in the same class or struct, or in a derived class.
private protected (added in C# 7.2)
The type or member can only be accessed by code in the same class or struct, or in a derived class from the same assembly, but not from another assembly.
internal
The type or member can be accessed by any code in the same assembly, but not from another assembly.
protected internal
The type or member can be accessed by any code in the same assembly, or by any derived class in another assembly.
When no access modifier is set, a default access modifier is used. So there is always some form of access modifier even if it's not set.
static modifier
The static modifier on a class means that the class cannot be instantiated, and that all of its members are static. A static member has one version regardless of how many instances of its enclosing type are created.
A static class is basically the same as a non-static class, but there is one difference: a static class cannot be externally instantiated. In other words, you cannot use the new keyword to create a variable of the class type. Because there is no instance variable, you access the members of a static class by using the class name itself.
However, there is a such thing as a static constructor. Any class can have one of these, including static classes. They cannot be called directly & cannot have parameters (other than any type parameters on the class itself). A static constructor is called automatically to initialize the class before the first instance is created or any static members are referenced. Looks like this:
static class Foo()
{
static Foo()
{
Bar = "fubar";
}
public static string Bar { get; set; }
}
Static classes are often used as services, you can use them like so:
MyStaticClass.ServiceMethod(...);
A graphical overview (summary in a nutshell)
Actually, it's a little bit more complicated than that.
Now (as of C# 7.2), there's also private protected, and it matters whether a derived class is in the same assembly or not.
So the overview needs to be expanded:
See also the C#-dotnet-docs on the subject.
Since static classes are sealed, they cannot be inherited (except from Object), so the keyword protected is invalid on static classes.
For the defaults if you put no access modifier in front, see here:
Default visibility for C# classes and members (fields, methods, etc.)?
Non-nested
enum public
non-nested classes / structs internal
interfaces internal
delegates in namespace internal
class/struct member(s) private
delegates nested in class/struct private
Nested:
nested enum public
nested interface public
nested class private
nested struct private
Also, there is the sealed-keyword, which makes a class not-inheritable.
Also, in VB.NET, the keywords are sometimes different, so here a cheat-sheet:
Public - If you can see the class, then you can see the method
Private - If you are part of the class, then you can see the method, otherwise not.
Protected - Same as Private, plus all descendants can also see the method.
Static (class) - Remember the distinction between "Class" and "Object" ? Forget all that. They are the same with "static"... the class is the one-and-only instance of itself.
Static (method) - Whenever you use this method, it will have a frame of reference independent of the actual instance of the class it is part of.
Reposting the awesome diagrams from this answer.
Here are all access modifiers in Venn diagrams, from more limiting to more promiscuous:
private:
private protected: - added in C# 7.2
internal:
protected:
protected internal:
public:
Yet another visual approach of the current access modifier (C# 7.2). Hopefully the schema helps to remember it easier
(click the image for interactive view.)
Outside Inside
If you struggle to remember the two-worded access modifiers, remember outside-inside.
private protected: private outside (the same assembly) protected inside (same assembly)
protected internal: protected outside (the same assembly) internal inside (same assembly)
using System;
namespace ClassLibrary1
{
public class SameAssemblyBaseClass
{
public string publicVariable = "public";
protected string protectedVariable = "protected";
protected internal string protected_InternalVariable = "protected internal";
internal string internalVariable = "internal";
private string privateVariable = "private";
public void test()
{
// OK
Console.WriteLine(privateVariable);
// OK
Console.WriteLine(publicVariable);
// OK
Console.WriteLine(protectedVariable);
// OK
Console.WriteLine(internalVariable);
// OK
Console.WriteLine(protected_InternalVariable);
}
}
public class SameAssemblyDerivedClass : SameAssemblyBaseClass
{
public void test()
{
SameAssemblyDerivedClass p = new SameAssemblyDerivedClass();
// NOT OK
// Console.WriteLine(privateVariable);
// OK
Console.WriteLine(p.publicVariable);
// OK
Console.WriteLine(p.protectedVariable);
// OK
Console.WriteLine(p.internalVariable);
// OK
Console.WriteLine(p.protected_InternalVariable);
}
}
public class SameAssemblyDifferentClass
{
public SameAssemblyDifferentClass()
{
SameAssemblyBaseClass p = new SameAssemblyBaseClass();
// OK
Console.WriteLine(p.publicVariable);
// OK
Console.WriteLine(p.internalVariable);
// NOT OK
// Console.WriteLine(privateVariable);
// Error : 'ClassLibrary1.SameAssemblyBaseClass.protectedVariable' is inaccessible due to its protection level
//Console.WriteLine(p.protectedVariable);
// OK
Console.WriteLine(p.protected_InternalVariable);
}
}
}
using System;
using ClassLibrary1;
namespace ConsoleApplication4
{
class DifferentAssemblyClass
{
public DifferentAssemblyClass()
{
SameAssemblyBaseClass p = new SameAssemblyBaseClass();
// NOT OK
// Console.WriteLine(p.privateVariable);
// NOT OK
// Console.WriteLine(p.internalVariable);
// OK
Console.WriteLine(p.publicVariable);
// Error : 'ClassLibrary1.SameAssemblyBaseClass.protectedVariable' is inaccessible due to its protection level
// Console.WriteLine(p.protectedVariable);
// Error : 'ClassLibrary1.SameAssemblyBaseClass.protected_InternalVariable' is inaccessible due to its protection level
// Console.WriteLine(p.protected_InternalVariable);
}
}
class DifferentAssemblyDerivedClass : SameAssemblyBaseClass
{
static void Main(string[] args)
{
DifferentAssemblyDerivedClass p = new DifferentAssemblyDerivedClass();
// NOT OK
// Console.WriteLine(p.privateVariable);
// NOT OK
//Console.WriteLine(p.internalVariable);
// OK
Console.WriteLine(p.publicVariable);
// OK
Console.WriteLine(p.protectedVariable);
// OK
Console.WriteLine(p.protected_InternalVariable);
SameAssemblyDerivedClass dd = new SameAssemblyDerivedClass();
dd.test();
}
}
}
Regarding the question of Nothing
Namespace types are internal by default
Any type member, including nested types are private by default
public - can be access by anyone anywhere.
private - can only be accessed from with in the class it is a part of.
protected - can only be accessed from with in the class or any object that inherits off of the class.
Nothing is like null but in VB.
Static means you have one instance of that object, method for every instance of that class.
Hmm.
See here: Access Modifiers.
In a nutshell:
Public gives the method or type complete visibility from other types/classes.
Private allows only the type containing the private method/variable access to the private method/variable (note that nested classes also have access to the containing classes private methods/variables).
Protected is similar to private except derived classes can also access protected methods.
"Nothing" is VB.NET's equivalent to null. Although if you're referring to "nothing" meaning "no access modifier", then it depends, although a very rough rule of thumb (certainly in C#) is that if you don't explicitly specify an access modifier, the method/variable declaration is usually as restricted as it can be.
i.e.
public class MyClass
{
string s = "";
}
is effectively the same as:
public class MyClass
{
private string s = "";
}
The linked MSDN article will offer a fully description when there's no access modifier explicitly specified.
mmm...
Static means that you can access that function without having an instance of the class.
You can access directly from the class definition.
A status of Private indicates that variables can only be accessed by objects of the same class. Protected status extends that access to include descendants of the class as well.
"from the above table we can see the deference between private and protected... am think both are same ....so what the need for that two separate command"
Check MSDN link for more information
public means that it can be accessed by any class in any assembly, which includes the class itself.
protected internal means it can be accessed by the class itself (in the class definition), and it can be accessed by any class in the current assembly, but outside of the assembly it can only be accessed by a class that inherits the class, or by the class itself (if it is a partial class) – basically it means internal inside the assembly and protected outside of the assembly.
protected means it can only be accessed by the class itself, or accessed by a class that inherits it and that class can be in any assembly
internal means it can be accessed by the class itself or by any class in the assembly but can't be accessed at all outside of the assembly unless by the class itself (i.e. it is a partial class)
private protected means it can only be accessed by the class itself, or it can be accessed by a class that inherits it and only if that class is in the current assembly. Outside of the assembly, it can only be accessed by the class itself (i.e. it is a partial class) – basically combines internal and protected, or another way of putting it is it's private outside of the assembly and protected inside the assembly.
private means that it can only be accessed by the class itself
no access modifier: The default access for everything in C# is "the most restricted access you could declare for that member"., which is private for a member / method / nested class in a class and internal for a non-nested class.
In the above text 'accessed' means accessed via an object of the class type, which within a method of the class itself will be the implicit this object, or perhaps the method instantiates an explicit object of the current class type and accesses it through that object. Both are considered to be being accessed by the class itself and therefore the access rules are the same. This also applies to an access being performed from a static method, or when it is a static member / method being accessed, except the access is performed using the class scope and not and object. A member / method of a static class needs to be explicitly made static or it won't compile.
Classes that are not nested can either be public or internal and are internal by default. Classes that are nested can be any access type, and if the parent class is static, it does not need to be static and neither do its members. An internal class means that it can only be instantiated or its static members accessed from the current assembly.
You can have a public member / method / nested class in an internal or private nested class -- only the access specifier (in the fully qualified name of the access that is being made) that is below the level required in the current access that is being made prevents the access.
Inheritance in C# is always public unlike C++, which can privately or protectedly inherit, which then changes the access of all classes that then inherit from the class that is inheriting from this class, as well as the access via object / via class scope of type of the class that inheriting privately / protectedly from the class and the class that is inheriting from the class that is inheriting privately / protectedly form the class, and so on. The access is changed such that all access modifiers less restrictive than private or protected are made private and protected respectively.
Careful! Watch the accessibility of your classes. Public and protected classes and methods are by default accessible for everyone.
Also, Microsoft isn't very explicit in showing access modifiers (public, protected, etc.. keywords) when new classes in Visual Studio are created. So, take good care and think about the accessibility of your class because it's the door to your implementation internals.
Those access modifiers specify where your members are visible. You should probably read this up. Take the link given by IainMH as a starting point.
Static members are one per class and not one per instance.
I think it is related to good OOP design. If you are a developer of a library you want to hide the inner workings of your library. That way, you can modify your library inner workings later on. So you put your members and helper methods as private, and only interface methods are public. Methods that should be overwritten should be protected.
C# has, in total, 6 access modifiers:
private: The member declared with this accessibility can be visible within the containing type, it is not visible to any derived types, other types in the same assembly or types outside of the containing assembly. i.e., access is limited to the containing type only.
protected: The member declared with this accessibility can be visible within the types derived from the containing type within the containing assembly, and the types derived from the containing type outside of the containing assembly. i.e., access is limited to derived types of the containing type.
internal: The member declared with this accessibility can be visible within the assembly containing this member, it is not visible to any assembly outside of the containing assembly. i.e., access is limited to containing assembly only.
internal protected: The member declared with this accessibility can be visible within the types derived from the containing type within or outside of the containing assembly, it is also visible to any types within the containing assembly. i.e., access is limited to containing assembly or derived types.
public: The member declared with this accessibility can be visible within the assembly containing this member, or any other assembly that references the containing assembly. i.e., access is not limited.
In C# 7.2, a new level of accessibility was added:
private protected: The member declared with this accessibility can be visible within the types derived from this containing type within the containing assembly. It is not visible to any types not derived from the containing type, or outside of the containing assembly. i.e., the access is limited to derived types within the containing assembly.
Source including a sample code of the new private protected access modifier
public The type or member can be accessed by any other code in the same assembly or another assembly that references it. The accessibility level of public members of a type is controlled by the accessibility level of the type itself.
private The type or member can be accessed only by code in the same class or struct.
internal Internal types or members are accessible only within files in the same assembly.
protected The type or member can be accessed only by code in the same class, or in a class that is derived from that class.
internal: The type or member can be accessed by any code in the same assembly, but not from another assembly. In other words, internal types or members can be accessed from code that is part of the same compilation.
protected internal: The type or member can be accessed by any code in the assembly in which it's declared, or from within a derived class in another assembly.
private protected The type or member can be accessed by types derived from the class that are declared within its containing assembly.
protected internal A protected internal member is accessible from the current assembly or from types that are derived from the containing class.
static modifier is used to declare a static member, which belongs to the type itself rather than to a specific object. The static modifier can be used to declare static classes. In classes, interfaces, and structs, you may add the static modifier to fields, methods, properties, operators, events, and constructors.
With C# 11 you can also use the file access modifier.
The file modifier restricts a top-level type's scope and visibility to the file in which it's declared. The file modifier will generally be applied to types written by a source generator. File-local types provide source generators with a convenient way to avoid name collisions among generated types.
// In File1.cs:
file interface IWidget
{
int ProvideAnswer();
}
file class HiddenWidget
{
public int Work() => 42;
}
public class Widget : IWidget
{
public int ProvideAnswer()
{
var worker = new HiddenWidget();
return worker.Work();
}
}
I have created another type of visualization. Maybe this can be better way to understand for someone
https://github.com/TropinAlexey/C-sharp-Access-Modifiers
All access modifiers' descriptions for C#