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Constructors of Classes

Constructors are special methods that produce a defined initial state for objects and classes. The state of an object is determined by its instance attributes and static attributes. Contents can be assigned to attributes using the addition VALUE of the statement DATA. Constructors are necessary when the initial state of an object is to be defined dynamically.

Like normal methods, there are two types of constructor: instance constructors and static constructors.

Special rules apply to constructors in cases of inheritance. These rules are not described in this document, but can be found here.

Other versions: 7.31 | 7.40 | 7.54

Instance Constructors

Each class has one instance constructor. This is a predefined instance method of the constructor class. To use the instance constructor, the constructor method must be declared in a visibility area of the class using the METHODS statement, and implemented in the implementation section. In global classes, the instance constructor can be declared in the public visibility area only, for technical reasons. In local classes, the visibility area in which the instance constructor can be declared must be more general or equal to the instantiability defined by the addition CREATE of the CLASS statement, where the most specialized area is recommended. Unless it is explicitly declared, the instance constructor is an implicit method, which inherits and accesses the interface from the instance constructor in the superclass.

Instance constructors are called once for each instance. They are called automatically, immediately after an instance is created using the statement CREATE OBJECT. It is not possible to call an instance constructor directly using the constructor( ... ); see super->constructor( ... ) in the inheritance.

An instance constructor can contain an interface with IMPORTING parameters and exceptions. The interface is defined using the same syntax as for regular methods in the statement METHODS. The fact that there are no exporting parameters shows that constructors only exist to define the state of an object and have no other function. To pass parameters and handle classic exceptions, use the EXPORTING and EXCEPTIONS additions of the CREATE OBJECT statement.

Static Constructors

Each class has a single static constructor. This is a predefined public static method of the constructor class. To use the static constructor, the static method class_constructor must be declared in the public section of the declaration part of the class using the CLASS-METHODS statement, and implemented in the implementation part. The static constructor has no interface parameters and cannot raise exceptions. Unless declared explicitly, the static constructor is merely an empty method.

The static constructor is called once per class and internal session. The static constructor of a class class is called automatically before the class is accessed for the first time. The static constructor is always called immediately before the class is accessed, with one exception: If the class is accessed for the first time only to address a static attribute, the static constructor is executed at the beginning of the processing block (dialog module, event block, procedure) in which access takes place.


  • The point at which the static constructor is called has not yet been finalized. We can currently ensure only that it will be called before the class is accessed for the first time. For this reason, static methods may be executed before the static constructor was ended.

  • The execution order of static constructors is dependent on the program flow. Static constructors must be implemented so that they can be executed in any order.


Visibility of Instance Constructors