Visibility Sections in Classes
The declaration section of a class can be split into up to four different visibility sections.
These sections define the external visibility of the class components and therefore the interfaces of the class for all users allowed by the package concept. Each component of a class must be explicitly assigned to one of the visibility sections. Only the friends of a class ignore the associated restrictions.
- Public visibility section
All components declared in the public visibility section defined with
PUBLIC SECTIONare accessible to all users as well as in the methods of all inheritors and the class itself. The public components of the class form the interface between the class and its users.
- Protected visibility section
All components declared in the protected visibility section defined with PROTECTED SECTION are accessible in the methods of all inheritors and in the class itself. Protected components form a special interface between a class and its subclasses.
- Private visibility section
All components declared in the private visibility section defined with
PRIVATE SECTIONare only accessible in the class itself, and are also not visible to the inheritors. The private components therefore do not form an interface to the users of the class.
The following table summarizes the visibilities of a class:
|Visible for||PUBLIC SECTION||PROTECTED SECTION||PRIVATE SECTION|
|Same class and its friends||X||X||X|
|Any repository objects||X||-||-|
A subclass can generally never access the protected components of a subclass from a different branch in the inheritance hierarchy, even if they are inherited from a common superclass. This rule can only be lifted by a friendship.
The three visibility sections form the basis for the important feature of encapsulation in ABAP Objects. When declaring a class, you should ensure you declare the minimum possible number of components in the public section and create these public components carefully. The public components of global classes may not be changed once you have released the class.
The class is the smallest encapsulation unit in ABAP Objects. A method can therefore use all components of all instances of the same class, except for the components of its own class. An exception to this rule are subclasses that cannot access the private components of superclasses, if they are not their friends.
m1 of class
c1, reference variables
of static type
c1 can be used to access the protected attribute
and the private attribute
a12 of any objects of
m2 of subclass
c2, reference variables
of static type
c2 can similarly be used
to access the protected attribute
a11. It is not possible to access the private attribute of the superclass with either reference variable.
CLASS c1 DEFINITION. PUBLIC SECTION. METHODS m1. PROTECTED SECTION. DATA a11 TYPE i. PRIVATE SECTION. DATA a12 TYPE i. ENDCLASS. CLASS c1 IMPLEMENTATION. METHOD m1. DATA lref1 TYPE REF TO c1. lref1->a11 = 0. "OK lref1->a12 = 0. "OK ENDMETHOD. ENDCLASS. CLASS c2 DEFINITION INHERITING FROM c1. PUBLIC SECTION. METHODS m2. ENDCLASS. CLASS c2 IMPLEMENTATION. METHOD m2. DATA: lref1 TYPE REF TO c1, lref2 TYPE REF TO c2. lref1->a11 = 0. "OK lref2->a11 = 0. "OK "lref1->a12 = 0. "Syntax error, access to a11 not permitted "lref2->a12 = 0. "Syntax error, a12 not visible ENDMETHOD. ENDCLASS.