SAP ABAP OBJECTS Tutorials

Polymorphism

Polymorphism: When the same method is implemented differently in different classes. This can be done using 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 (Se Subcallsing)  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: / ‘I am a dog and my 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 <Event handler method>

*    FOR <ref_sender>!FOR ALL INSTANCES [ACTIVATION <var>]

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. I have not eaten for more than’,

ex_time_since_last_meal, ‘ hours’.

WRITE: / ‘Give me 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!

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