Interfaces
In ABAP interfaces are implemented in addition to, and independently of classes. An interface only has a declaration part, and do not have visibillity sections. Components (Attributes, methods, constants, types) can be defined the same way as in classes.
· Interfaces are listed in the definition part lof the class, and must always be in the PUBLIC SECTION.
· Operations defined in the interface atre impemented as methods of the class. All methods of the interface must be present in the
· implementation part of the class.
· Attributes, events, constants and types defined in the interface are automatically available to the class carying out the implementation.
· Interface components are adresse in the class by <interface name>~<component name>
Example of how to implement an interface:
INTERFACE lif_document
DATA: author type ref to lcl_author.
METHODS: print,
display.
ENDINTERFACE.
CLASS lcl_text_document DEFINITION.
PUBLIC SECTION.
INTERFACES lif_document.
METHODS display.
ENDCLASS.
CLASS lcl_text_document IMPLEMENTTION.
METHOD lif_document~print.
ENDMETHOD.
METHOD lif_document~display
ENDMETHOD.
METHOD display.
ENDMETHOD.
ENDCLASS.
REPORT zzz.
DATA: text_doc TYPE REF TO lcl_document.
Start-of-selection.
CREATE OBJECT text_doc.
CALL METHOD text_doc->lif_document~print.
CALL METHOD text_doc->lif_document~display.
CALL METHOD text_doc->display.
Events
For events of controls, refer to How to use controls.
· Events can only have EXPORTING parameters
· When an event is triggerede, only those events handlers that have registred themselves using SET HANDLER by this point of runtime are
· executed. You can register an event using ACTIVATION ‘X’ and derigert it by using ACTIVATION ‘SPACE’.
Defining events:
CLASS <classname> DEFINITION.
EVENTS: <event> EXPORTING VALUE (<ex_par>) TYPE type.
CLASS <classname> IMPLEMENTATION.
METHOD <m>:
RAISE EVENT <event> EXPORTING <ex_par> = <act_par>.
Handling events:
CLASS <classname> DEFINITION.
METHODS: <on_event> FOR <event> OF <classname> ! <interface> IMPORTING <imp_par1>…<imp_parN> SENDER.
Setting handler
SET HANDLER <ref_handle> <on_event> FOR <ref_sender> ! FOR ALL INSTANCES
[ACTIVATION <var>]
Define, implement and use simple class
***INCLUDE ZBC404_HF_LCL_AIRPLANE .
******************************************
* Definition part
******************************************
CLASS lcl_airplane DEFINITION.
*——————————
* Public section
*——————————
PUBLIC SECTION.
TYPES: t_name(25) TYPE c.
METHODS:
constructor,
set_attributes IMPORTING p_name TYPE t_name
p_planetype TYPE saplane-planetype,
display_attributes,
display_n_o_airplanes.
*——————————
* Private section
*——————————
PRIVATE SECTION.
* Private attributes
DATA: name(25) TYPE c,
planetype TYPE saplane-planetype.
* Private static attribute
CLASS-DATA n_o_airplanes TYPE i.
ENDCLASS.
******************************************
* Implementation part
******************************************
CLASS lcl_airplane IMPLEMENTATION.
METHOD constructor.
* Counts number of instances
n_o_airplanes = n_o_airplanes + 1.
ENDMETHOD.
METHOD set_attributes.
name = p_name.
planetype = p_planetype.
ENDMETHOD.
METHOD display_attributes.
WRITE:/ ‘Name:’, name, ‘Planetype:’, planetype.
ENDMETHOD.
METHOD display_n_o_airplanes.
WRITE: / ‘No. planes:’, n_o_airplanes.
ENDMETHOD.
ENDCLASS.
REPORT zbc404_hf_maintain_airplanes .
INCLUDE zbc404_hf_lcl_airplane.
* Create reference to class lcl_airplane
DATA: airplane1 TYPE REF TO lcl_airplane,
airplane2 TYPE REF TO lcl_airplane.
START-OF-SELECTION.
* Create instance
CREATE OBJECT airplane1.
CALL METHOD: airplane1->display_n_o_airplanes.
CREATE OBJECT airplane2.
* Setting attributes using a method with parameters
CALL METHOD airplane1->set_attributes EXPORTING p_name = ‘Kurt’
p_planetype = ‘MD80’.
END-OF-SELECTION.
* Using methods
CALL METHOD: airplane1->display_n_o_airplanes,
airplane1->display_attributes.
The resulting report:
Maintain airplanes
No. planes: 1
No. planes: 2
Name: Kurt Planetype: MD80
Use constructor to create an object with parameters
CLASS lcl_airplane DEFINITION.
PUBLIC SECTION.
TYPES: t_name(25) TYPE c.
METHODS:
constructor importing p2_name type t_name
p2_planetype TYPE saplane-planetype,
….. more code …….
CLASS lcl_airplane IMPLEMENTATION.
METHOD constructor.
name = p2_name.
planetype = p2_planetype.
….. more code …….
START-OF-SELECTION.
CREATE OBJECT airplane1 exporting p2_name = ‘Hansemand’
p2_planetype = ‘Boing 747’.
Subclassing
This example uses a superclass LCL_AIRPLANE and subclasses it into LCL_PASSENGER_AIRPLANE and LCL_CARGO_PLANE.
LCL_AIRPLANE has a method display_n_o_airplanes that displays the number of object instances.
LCL_PASSENGER_AIRPLANE has the private instance attribute n_o_seats, and redefines the superclass method display_attributes, so it also displays n_o_seats.
LCL_CARGO_PLANE has the private instance attribute cargomax, and redefines the superclass method display_attributes, so it also displays cargomax.
All instance attributes are provided by the cunstructor method.
Superclass LCL_AIRPLANE
***INCLUDE ZBC404_HF_LCL_AIRPLANE .
******************************************
* Definition part
******************************************
CLASS lcl_airplane DEFINITION.
*——————————
* Public section
*——————————
PUBLIC SECTION.
TYPES: t_name(25) TYPE c.
METHODS:
constructor IMPORTING im_name TYPE t_name
im_planetype TYPE saplane-planetype,
display_attributes.
* Static methods
CLASS-METHODS:
display_n_o_airplanes.
*——————————
* Protected section
*——————————
PROTECTED SECTION.
* Private attributes
DATA: name(25) TYPE c,
planetype TYPE saplane-planetype.
* Private static attribute
CLASS-DATA n_o_airplanes TYPE i.
ENDCLASS.
******************************************
* Implementation part
******************************************
CLASS lcl_airplane IMPLEMENTATION.
METHOD constructor.
name = im_name.
planetype = im_planetype.
* Counts number of instances
n_o_airplanes = n_o_airplanes + 1.
ENDMETHOD.
METHOD display_attributes.
WRITE:/ ‘Name:’, name, ‘Planetype:’, planetype.
ENDMETHOD.
METHOD display_n_o_airplanes.
WRITE: / ‘No. planes:’, n_o_airplanes.
ENDMETHOD.
ENDCLASS.
Sub class LCL_PASSENGER_AIRPLANE
***INCLUDE ZBC404_HF_LCL_PASSENGER_PLANE .
*******************************************************************
* This is a subclass of class lcl_airplane
*******************************************************************
CLASS lcl_passenger_airplane DEFINITION INHERITING FROM lcl_airplane.
PUBLIC SECTION.
* The constructor contains the parameters from the superclass
* plus the parameters from the subclass
METHODS:
constructor IMPORTING im_name TYPE t_name
im_planetype TYPE saplane-planetype
im_n_o_seats TYPE sflight-seatsmax,
* Redefinition of superclass method display_attributes
display_attributes REDEFINITION.
PRIVATE SECTION.
DATA: n_o_seats TYPE sflight-seatsmax.
ENDCLASS.
CLASS lcl_passenger_airplane IMPLEMENTATION.
METHOD constructor.
* The constructor method of the superclass MUST be called withing the
* construtor
CALL METHOD super->constructor
EXPORTING im_name = im_name
im_planetype = im_planetype.
n_o_seats = im_n_o_seats.
ENDMETHOD.
* The redefined display_attributes method
METHOD display_attributes.
CALL METHOD super->display_attributes.
WRITE: / ‘No. seats:’, n_o_seats.
ENDMETHOD.
ENDCLASS.
Sub class LCL_CARGO_PLANE
***INCLUDE ZBC404_HF_LCL_CARGO_PLANE .
*******************************************************************
* This is a subclass of class lcl_airplane
*******************************************************************
CLASS lcl_cargo_plane DEFINITION INHERITING FROM lcl_airplane.
PUBLIC SECTION.
METHODS:
* The constructor contains the parameters from the superclass
* plus the parameters from the subclass
constructor IMPORTING im_name TYPE t_name
im_planetype TYPE saplane-planetype
im_cargomax type scplane-cargomax,
* Redefinition of superclass method display_attributes
display_attributes REDEFINITION.
PRIVATE SECTION.
DATA:cargomax TYPE scplane-cargomax.
ENDCLASS.
CLASS lcl_cargo_plane IMPLEMENTATION.
METHOD constructor.
* The constructor method of the superclass MUST be called withing the
* constructor
CALL METHOD super->constructor
EXPORTING im_name = im_name
im_planetype = im_planetype.
cargomax = im_cargomax.
ENDMETHOD.
METHOD display_attributes.
* The redefined display_attributes method
CALL METHOD super->display_attributes.
WRITE: / ‘Cargo max:’, cargomax.
ENDMETHOD.
ENDCLASS.
The Main program that uses the classes
REPORT zbc404_hf_main .
* Super class
INCLUDE zbc404_hf_lcl_airplane.
* Sub classes
INCLUDE zbc404_hf_lcl_passenger_plane.
INCLUDE zbc404_hf_lcl_cargo_plane.
DATA:
* Type ref to sub classes. Note: It is not necesssary to make typeref to the superclass
o_passenger_airplane TYPE REF TO lcl_passenger_airplane,
o_cargo_plane TYPE REF TO lcl_cargo_plane.
START-OF-SELECTION.
* Display initial number of instances = 0
CALL METHOD lcl_airplane=>display_n_o_airplanes.
* Create objects
CREATE OBJECT o_passenger_airplane
EXPORTING
im_name = ‘LH505’
im_planetype = ‘Boing 747’
im_n_o_seats = 350.
CREATE OBJECT o_cargo_plane
EXPORTING
im_name = ‘AR13’
im_planetype = ‘DC 3’
im_cargomax = 35.
* Display attributes
CALL METHOD o_passenger_airplane->display_attributes.
CALL METHOD o_cargo_plane->display_attributes.
* Call static method display_n_o_airplanes
* Note: The syntax for calling a superclass method, differs from the syntax when calling a subclass method.
* When calling a superclass => must be used instead of ->
CALL METHOD lcl_airplane=>display_n_o_airplanes.
Result:
No. planes: 0
Name: LH505 Planetype: Boing 747
No. seats: 350
Name: AR13 Planetype: DC 3
Cargo max: 35,0000
No. planes: 2