Modifier

Access Modifiers

Access modifiers are keywords used to specify the declared accessibility of types and type members. The four access modifiers are discussed in the table below:

Access Modifier	Meaning
public	public is an access modifier for types and type members. This is the most permissive access level as there are no restrictions on accessing a public type or type member.
internal	internal is an access modifier for types and type members. internal members are accessible only within file of the same assembly. It is an error to reference an internal type or internal type member outside the assembly within which it was declared. A common use of internal access is in component-based development because it enables a group of components to interact in a private matter without being exposed to the outer world. For example, a Data Access Layer could have several classes with internal members that are only used by the DAL.
protected	protected is an access modifier for type members only. A protected member is only accessible within the body of the containing type and from within any classes derived from the containing type.
private	private is an access modifier for type members only. private access is the least accessible and such members are only accessible within the body of the containing type. Note that nested types within the same containing body can also access those private members.

Accessibility Levels

The four access modifiers listed above result in five accessibility levels shown below. Note how certain accessibility levels are not permitted depending on the context in which an access modifiers was used:

Accessibility Level	Meaning	Applies To Namespaces	Applies To Types	Applies To Type Members
public	Access is not restricted.	Yes	Yes	Yes
internal	Access is limited to the current assembly (project).	No	Yes	Yes
protected	Access is limited to the containing class, and classes derived from the containing class	No	No	Yes
internal protected	Access is limited to the current assembly (project), the containing class, and classes derived from the containing class	No	No	Yes
private	Access is limited to the containing type.	No	No	Yes

The following table illustrates accessibility levels for namespaces, types, and type members. Note that namespace elements (i.e., classes, structs, interfaces and enum) can only have public or internaldeclared accessibility. Access modifiers private, protected,  and protected internal are not allowed on namespace members. 

Context	Default Accessibility	Allowed Declared Accessibility	Default Member Accessibility	Allowed Declared Accessibility On Members
namespace	public	None	Internal	public internal
class	internal (if top level)	public internal	private	public protected internal internal protected private
interface	internal (if top level)	public internal	public	None
struct	internal (if top level)	public internal	private	public internal private
enum	internal (if top level)	public internal	pubic	None