Access Modifiers

C# provides 4 access modifiers for classes, fields, etc.: public, internal, protected, and private. For simplicity, however, we will not allow the use of the internal or protected access modifiers unless they are required by the compiler (for example, when overriding a protected method).

When classes, fields, etc., are declared, C# does not require that an access modifier be used. If the access modifier is omitted, a default accessibility level will be used. However, the default depends on where it is being declared. For example, the default accessibility level of a top-level type is internal, whereas the default accessibility level of a class member is private. In order to avoid confusion, we will require that access modifiers (i.e., public or private) be used on all declarations except where C# does not allow them (C# does not allow access modifiers for namespaces, members of interfaces or enumerations, or local variables within methods). In particular, note that when Visual Studio® automatically generates a class statement, it does not always supply an access modifier, or it may use internal. We require that the statement be changed to use public (C# does not allow private here).

In addition, fields within classes and structures should be declared private, unless they are also declared either const or readonly. If you want to make a variable accessible to outside code, you can instead do something like the following:

public double Force { get; set; }

Or if you want the outside code to be able to access it, but you don’t want it to change its value you can instead define it as:

public double Force { get; private set; }

In these examples, Force is not a field, but a property. It can be used like a field, but defining it as a property makes it more maintainable (see “Properties” for more details).

For more information on access modifiers and accessibility levels, see the section on Accessibility Levels in the C# Reference.