Inheritance V - Access Control

Class Access Control

• Private: Only code from the given class can access
• Package Private (default): Classes that belong in the same package can access, but not subclasses
  • Prevent third-party extension modification
• Protected: Classes within the same package and subclasses can access these members
  • Subtypes might need it, but subtype clients will not
• Public: Open access to everyone
  • Promise of accessibility
  • Giving up a public: not removed but deprecated

Modifier	Class	Package	Subclass	World
public	Y	Y	Y	Y
protected	Y	Y	Y	N
package private	Y	Y	N	N
private	Y	N	N	N

Subtleties

Default Package

Cause:

• Everything unspecified belong to the default package
• Default: package private

Result:

• All members of default package are accessible between the default-package classes

Access is Based Only on Static Types

The access depends only on the static types.

Interfaces Defaults Public

For interfaces, the default access for its methods is actually public, and not package-private.