Access Modifiers in C#

Access Modifiers are used to control the visibility of a type (classes, interfaces, structures, enumerations, and delegates) or their members (properties, methods, constructors, and fields) to other parts of an application.

Role of each access modifier and where it may be applied:

Access Modifier	Applicable to	Description
public	Types or type members	Public items have no access restrictions. A public member can be accessed from an object, as well as any derived class. It can also be accessed from other external assemblies.
private	Type members or nested types	Private items can only be accessed by the class (or structure) that defines the item.
protected	Type members or nested types	Protected items can be used by the class which defines it, and any child class. However, protected items cannot be accessed from the outside world using the C# dot operator.
internal	Type or type members	Internal items are accessible only within the current assembly. Therefore, if you define a set of internal types within a .NET class library, other assemblies are not able to make use of them.
protected internal	Type members or nested types	When the protected and internal keywords are combined on an item, the item is accessible within the defining assembly, the defining class, and by derived classes.

Note: By default, type members (ex. members of a class) are implicitly private while types (ex. classes) are implicitly internal.

// An internal class with a private default constructor.

class Country

{

// default constructor – implicitly private

Country()

{

}

}

Note: Nested types can have private access, but non-nested types cannot be marked private.

public class Country

{

// OK! Nested types can be marked private.

private enum FlagColor

{

Red, Green, Blue

}

}

Here, it is permissible to apply the private access modifier on the nested type. However, non-nested types (such as the Country) can only be defined with the public or internal modifiers.

// Error! Nonnested types cannot be marked private!

private class Country

{}