Classes and Inheritance - Illustrated C# 2005 - page 156

Class Access Modifiers
A class can be seen and accessed by other classes in the system. This section covers the acces-
sibility of classes. Although I will use classes in the explanations and examples, since that is
what you are familiar with at this point in the text, the accessibility rules also apply to the other
types I will cover later.
The term visible is sometimes used for the term accessible . They can be used interchange-
ably. There are two levels of class accessibility— public and internal .

￿A class marked public can be accessed by code from any assembly in the system. To
make a class visible to other assemblies, use the public access modifier, as shown here.

Keyword
↓
public class MyBaseClass
{ ...

￿A class marked internal can be seen only by classes within its own assembly.
- This is the default accessibility level, so unless you explicitly specify the modifier

public in the class declaration, code outside the assembly cannot access the class.

You can explicitly declare a class as internal by using the internal access modifier. -

Keyword
↓
internal class MyBaseClass
{ ...

Figure 7-13 illustrates the accessibility of internal and public classes from outside the
assembly. Class MyClass is not visible to the classes in the assembly on the left, because it is
marked internal . Class OtherClass , however, is visible to the classes on the left, because it
is marked public .

Figure 7-13. Classes from other assemblies can access public classes but cannot access internal
classes.