NAMES

Determining Accessibility

6.6.1

6.6   Qualified Names and Access Control

Qualified names are a means of access to members of packages and reference

types; related means of access include field access expressions ( 15.10) and

method invocation expressions ( 15.11). All three are syntactically similar in that

a  

.

  token appears, preceded by some indication of a package, type, or expres 

sion having a type and followed by an

Identifier

 that names a member of the pack 

age or type. These are collectively known as constructs for

qualified access

.

Java provides mechanisms for

access control

, to prevent the users of a pack 

age or class from depending on unnecessary details of the implementation of that

package or class. Access control applies to qualified access and to the invocation

of constructors by class instance creation expressions ( 15.8), explicit constructor

invocations ( 8.6.5), and the method

newInstance

 of class

Class

 ( 20.3.6).

If access is permitted, then the accessed entity is said to be

accessible

.

6.6.1   Determining Accessibility

Whether a package is accessible is determined by the host system ( 7.2).

If a class or interface type is declared

public

, then it may be accessed by any

Java code that can access the package in which it is declared. If a class or

interface type is not declared

public

, then it may be accessed only from

within the package in which it is declared.

A member (field or method) of a reference (class, interface, or array) type or a

constructor of a class type is accessible only if the type is accessible and the

member or constructor is declared to permit access:

N

If the member or constructor is declared

public

, then access is permitted.

All members of interfaces are implicitly

public

.

N

Otherwise, if the member or constructor is declared

protected

, then access

is permitted only when one of the following is true:

Access to the member or constructor occurs from within the package

containing the class in which the

protected

 member is declared.

Access occurs within a subclass of the class in which the

protected

member is declared, and the access is correct as described in  6.6.2.

N

Otherwise, if the member or constructor is declared

private

, then access is

permitted only when it occurs from within the class in which it is declared.

N

Otherwise, we say there is default access, which is permitted only when the

access occurs from within the package in which the type is declared.

99