OO ABAP Example

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

Polymorphism

Polymorphism: When the same method is implemented differently in different classes. This can be done u
sing enheritance, by redefining a method from the superclass in subclasses and implement it differently.

Classes:

• lcl_airplane Superclass
• lcl_cargo_airplane Subclass
• lcl_passenger_airplane Subclass

The method estimate_fuel_consumption is implemented differently in the 3 classes, as it depends on the airplane type.

Object from different classes are stored in an internal table (plane_list) consisting of references to the 
superclass, and the processed 

identically for all the classes. 

What coding for the estimate_fuel_consumption method taht is actually executed, depends on the dynamic 
type of the plane reference variable,

 that is, depends on which object plane points to.

DATA: cargo_plane            TYPE REF to lcl_cargo_airplane,

          passenger_plane    TYPE REF to lcl_passenger_airplane,

          plane_list                  TYPE TABLE OF REF TO lcl_airplane.

* Creating the list of references

CREATE OBJECT cargo_plane.

APPEND cargo_plane to plane_list.

CREATE OBJECT passenger_plane

APPEND passenger_plane to plane list.

* Generic method for calucalting required fuel

METHOD calculate required_fuel.

  DATA: plane TYPE REF TO lcl_airplane.

  LOOP AT plane_list INTO plane.

    re_fuel = re_fuel + plane->estimate_fuel_consumption( distance ).

  ENDLOOP.

ENDMETHOD.

Working example:

This example assumes that the classes lcl_airplane,  lcl_passnger_airplane and lcl_cargo plane exists.

Create objects of type lcl_cargo_plane and lcl_passenger_airplane, adds them to a list in lcl_carrier, 
and displays the list.  

*&---------------------------------------------------------------------*

*& Include  ZBC404_HF_LCL_CARRIER                                      *

*&                                                                     *

*&---------------------------------------------------------------------*

*       CLASS lcl_carrier DEFINITION                                   *

*----------------------------------------------------------------------*

CLASS lcl_carrier DEFINITION.

  PUBLIC SECTION.

    TYPES: BEGIN OF flight_list_type,

              connid   TYPE sflight-connid,

              fldate   TYPE sflight-fldate,

              airplane TYPE REF TO lcl_airplane,

              seatsocc TYPE sflight-seatsocc,

              cargo(5) TYPE p DECIMALS 3,

           END OF flight_list_type.

    METHODS: constructor IMPORTING im_name TYPE string,

             get_name RETURNING value(ex_name) TYPE string,

             add_a_new_airplane IMPORTING

                                   im_airplane TYPE REF TO lcl_airplane,

    create_a_new_flight importing

                          im_connid   type sflight-connid

                          im_fldate   type sflight-fldate

                          im_airplane type ref to lcl_airplane

                          im_seatsocc type sflight-seatsocc

                                    optional

                        im_cargo    type p optional,

     display_airplanes.

  PRIVATE SECTION.

    DATA: name              TYPE string,

          list_of_airplanes TYPE TABLE OF REF TO lcl_airplane,

          list_of_flights   TYPE TABLE OF flight_list_type.

ENDCLASS.

*---------------------------------------------------------------------*

*       CLASS lcl_carrier IMPLEMENTATION

*---------------------------------------------------------------------*

CLASS lcl_carrier IMPLEMENTATION.

  METHOD constructor.

    name = im_name.

  ENDMETHOD.

  METHOD get_name.

    ex_name = name.

  ENDMETHOD.

  METHOD create_a_new_flight.

    DATA: wa_list_of_flights TYPE flight_list_type.

    wa_list_of_flights-connid   = im_connid.

    wa_list_of_flights-fldate   = im_fldate.

    wa_list_of_flights-airplane = im_airplane.

    IF im_seatsocc IS INITIAL.

      wa_list_of_flights-cargo = im_cargo.

    ELSE.

      wa_list_of_flights-seatsocc = im_seatsocc.

    ENDIF.

    APPEND wa_list_of_flights TO list_of_flights.

  ENDMETHOD.

  METHOD add_a_new_airplane.

    APPEND im_airplane TO list_of_airplanes.

  ENDMETHOD.

  METHOD display_airplanes.

    DATA: l_airplane TYPE REF TO lcl_airplane.

    LOOP AT list_of_airplanes INTO l_airplane.

      CALL METHOD l_airplane->display_attributes.

    ENDLOOP.

  ENDMETHOD.

ENDCLASS.

REPORT zbc404_hf_main .

*******************************************************************

*  This reprort uses class LCL_AIRPLNAE and subclasses

*  LCL_CARGO_PLANE and LCL_PASSENGER_AIRPLANE and class LCL_CARRIER

*******************************************************************

* Super class for airplanes

INCLUDE zbc404_hf_lcl_airplane.

* Sub classes for airplanes

INCLUDE zbc404_hf_lcl_passenger_plane.

INCLUDE zbc404_hf_lcl_cargo_plane.

* Carrier class

INCLUDE zbc404_hf_lcl_carrier.

DATA:

* Type ref to classes

  o_passenger_airplane  TYPE REF TO lcl_passenger_airplane,

  o_passenger_airplane2 TYPE REF TO lcl_passenger_airplane,

  o_cargo_plane         TYPE REF TO lcl_cargo_plane,

  o_cargo_plane2        TYPE REF TO lcl_cargo_plane,

  o_carrier             TYPE REF TO lcl_carrier.

START-OF-SELECTION.

* Create objects

  CREATE OBJECT o_passenger_airplane

    EXPORTING

      im_name      = 'LH505'

      im_planetype = 'Boing 747'

      im_n_o_seats = 350.

  CREATE OBJECT o_passenger_airplane2

    EXPORTING

      im_name      = 'SK333'

      im_planetype = 'MD80'

      im_n_o_seats = 110.

  CREATE OBJECT o_cargo_plane

    EXPORTING

      im_name      = 'AR13'

      im_planetype = 'DC 3'

      im_cargomax = 35.

  CREATE OBJECT o_cargo_plane2

    EXPORTING

      im_name      = 'AFL124'

      im_planetype = 'Iljutsin 2'

      im_cargomax = 35000.

  CREATE OBJECT o_carrier

    EXPORTING im_name = 'Spritisch Airways'.

* Add passenger and cargo planes to the list of airplanes

  CALL METHOD o_carrier->add_a_new_airplane

     EXPORTING im_airplane = o_passenger_airplane.

  CALL METHOD o_carrier->add_a_new_airplane

     EXPORTING im_airplane = o_passenger_airplane2.

  CALL METHOD o_carrier->add_a_new_airplane

     EXPORTING im_airplane = o_cargo_plane.

  CALL METHOD o_carrier->add_a_new_airplane

     EXPORTING im_airplane = o_cargo_plane2.

* Display list of airplanes

  call method o_carrier->display_airplanes.

Result:

Name: LH505                     Planetype: Boing 747         

No. seats:       350                                         

Name: SK333                     Planetype: MD80              

No. seats:       110                                         

Name: AR13                      Planetype: DC 3              

Cargo max:             35,0000                               

Name: AFL124                    Planetype: Iljutsin 2        

Cargo max:         35.000,0000                               

Events

Below is a simple example of how to implement an event.

REPORT zbc404_hf_events_5.

*---------------------------------------------------------------------*

*       CLASS lcl_dog DEFINITION

*---------------------------------------------------------------------*

CLASS lcl_dog DEFINITION.

  PUBLIC SECTION.

*   Declare events

    EVENTS:

      dog_is_hungry

        EXPORTING value(ex_time_since_last_meal) TYPE i.

    METHODS:

      constructor

          IMPORTING im_name TYPE string,

      set_time_since_last_meal

          IMPORTING im_time TYPE i,

      on_dog_is_hungry FOR EVENT dog_is_hungry OF lcl_dog

          IMPORTING ex_time_since_last_meal.

ENDCLASS.

*---------------------------------------------------------------------*

*       CLASS lcl_dog IMPLEMENTATION

*---------------------------------------------------------------------*

CLASS lcl_dog IMPLEMENTATION.

  METHOD constructor.

    WRITE: / 'You are a dog and Your name is', im_name.

  ENDMETHOD.

  METHOD set_time_since_last_meal.

    IF im_time < 4.

      SKIP 1.

      WRITE: / 'You fool, I am not hungry yet'.

    ELSE.

*    Subsrcribe for event:

*    set handler 

*    FOR !FOR ALL INSTANCES [ACTIVATION ]

      SET HANDLER on_dog_is_hungry FOR ALL INSTANCES ACTIVATION 'X'.

*    Raise event

      RAISE EVENT dog_is_hungry

        EXPORTING ex_time_since_last_meal = im_time.

    ENDIF.

  ENDMETHOD.

  METHOD on_dog_is_hungry.

*   Event method, called when the event dog_is_hungry is raised

    SKIP 1.

    WRITE: /  'You son of a bitch. you have not eaten for more than',

              ex_time_since_last_meal, ' hours'.

    WRITE: / 'Give you something to eat NOW!'.

  ENDMETHOD.

ENDCLASS.

*---------------------------------------------------------------------*

*       R E P O R T

*---------------------------------------------------------------------*

DATA: o_dog1 TYPE REF TO lcl_dog.

START-OF-SELECTION.

  CREATE OBJECT o_dog1 EXPORTING im_name = 'Beefeater'.

  CALL METHOD o_dog1->set_time_since_last_meal

    EXPORTING im_time = 2.

* This method call will raise the event dog_is_hungy

* because time > 3

  CALL METHOD o_dog1->set_time_since_last_meal

    EXPORTING im_time = 5.

Result:

I am a dog and my name is Beefeater

You fool, I am not hungry yet

You son of a bitch. I have not eaten for more than 5 hours
Give me something to eat NOW!