ABAP Keyword Documentation → ABAP Programming Guidelines → Architecture → Object-Oriented Programming
Other versions: 7.31 | 7.40 | 7.54
When you define an ABAP class, you specify who creates an instance of this class or who may access the
instance constructor of the class. To do this, you use the addition
of the statement
CLASS ... DEFINITION. The addition CREATE
PUBLIC is the default setting and allows for the instancing by any user of the class. By specifying
CREATE PROTECTED, you can restrict the object creation to the class itself
and its subclasses. Using the addition
CREATE PRIVATE addition, objects can only be created by the class itself. The restriction of the object creation to the class itself is useful in connection with the
singleton design pattern, for example, where the class itself performs the object creation.
From a technical point of view, the instance constructor can be declared in all visibility sections
that are more general or equal to the instantiation specified in the addition
of the statement
CLASS ... DEFINITION, using the statement
constructor. However, the actual visibility is controlled by the addition
Declare the instance constructor in the public visibility section.
Always declare the instance constructor of a global class in its public visibility section and independently of the instantiation specified by the addition
CREATE in the class definition.
The components of global classes are stored internally, separated according to the visibility section
they belong to. Depending on the usage type of the class, only parts of the class are respected by ABAP
Compiler in compilations. This procedure requires that the constructor of a global class is always declared
in the public visibility section of the class. For these technical reasons, the instance constructor of a global class is always supposed to be declared in the public visibility section
PUBLIC SECTION). If it is declared in another visibility section, this may produce unjustified syntax errors in individual cases when global classes are used.
The technical restrictions mentioned only apply to the processing of global classes. Within local classes,
the instance constructor can also be defined in other visibility sections. However, this positioning
should correspond with the visibility section specified using the addition
A strategy like this enables you to use types for the interface of the instance constructor of a local class that are only accessible in a restricted visibility section.