topic final in Application Development and Automation Discussions

final

Former Member — Thu, 05 Jul 2007 06:51:15 GMT

what is the significance of final keyword in abap,How can we avoid a class being inherited by another class

Re: final

jaideeps — Thu, 05 Jul 2007 08:02:33 GMT

hi,

final keyword denotes that it is the final implementation for that method or variable or class. You can’t override that method/variable/class any more.

and using this final keyword we can avoid a class being inherited by other..

these are the concepts related to java..in J2e versions it will support..

thanks

jaideep

if useful reward points

Re: final

Former Member — Thu, 05 Jul 2007 08:22:11 GMT

Hi Sandeep,

IN ABAP, the key word FINAL can be used with class definition and method definition.

1. If we define a class as final , we cannot INHERIT from this calss.

Class CLASS1 DEFINITION FINAL INHERITING FROM SUPER_CLASS.

This is possible.

But

Class CLASS2 DEFINITION FINAL INHERITING FROM CLASS1.

THis is not possible as we have defined CLASS1 as final class.

2. If we define a method as final, it cannot be REDEFINED in sub classwes.

Eg.

CLASS CLASS1 DEFINITON

PUBLIC SECTION.

METHODS: METHOD1 FINAL.

ENDCLASS.

Then,

CLASS CLASS2 DEFINITION INHERITING FROM CLASS1.

PUBLIC SECTION.

METHODS: METHOD1 REDIFINITION.

ENDCLASS.

This is not possible as we have defined METHOD1 as FINAL in CLASS1.

Please reward with points if it is useful.

Re: final

Former Member — Fri, 06 Jul 2007 05:41:14 GMT

Hi Sundeep,

If this answer was helpful , please reward with points.

Re: final

Former Member — Fri, 06 Jul 2007 07:13:06 GMT

Hi Sandeep,

If we add "FINAL" addition to a class, no other class no subclasses can be inherited. It marks the last node of Inheritance tree. All methods in a Final class are automatically Final.

In a class which is not final, a method can be defined as FINAL. Such a

method cannot be redefined in a subclass.

Please see the example program.

&----

*& Class (Definiton) zl_lcl_vehicle

&----

Definition of Superclass *

----

CLASS zl_lcl_vehicle DEFINITION.

PUBLIC SECTION.

METHODS: set_make IMPORTING im_make TYPE string

im_model TYPE string,

get_make EXPORTING ex_make TYPE string

ex_model TYPE string,

Final Methods cannot be redefined in subclasses. Final methods *
cannot also be abstract. The constructors of the class are always *
final implicitly. *

get_n_o_veh_type FINAL EXPORTING ex_veh_typ TYPE i.

PRIVATE SECTION.

DATA: gv_make TYPE string, " Vehicle make

gv_model TYPE string. " Type or model

CLASS-DATA gv_veh_type_cnt TYPE i.

ENDCLASS. "zl_lcl_vehicle DEFINITION

&----

*& Class (Implementation) zl_lcl_vehicle

&----

Implementation of Superclass *

----

CLASS zl_lcl_vehicle IMPLEMENTATION.

METHOD set_make.

IF im_make IS NOT INITIAL

AND im_model IS NOT INITIAL.

gv_make = im_make.

gv_model = im_model.

ENDIF.

ENDMETHOD. "set_make

METHOD get_make.

ex_make = gv_make.

ex_model = gv_model.

ENDMETHOD. "get_make

This method is used to count the number of vehicle types. *
This number is later used to asign a vehicle code for a vehicle type *

METHOD get_n_o_veh_type.

gv_veh_type_cnt = gv_veh_type_cnt + 1.

ex_veh_typ = gv_veh_type_cnt.

ENDMETHOD. "get_n_o_veh_type

ENDCLASS. "zl_lcl_vehicle

&----

*& Class (Definiton) zl_lcl_car

&----

Definition of Subclass *
This class is defined as FINAL which means it can't be *
inherited. Final classes are the last branch in an *
inheritance tree. In a final classes, the declaration of *
protected components is synonymous with the declaration of *
private components. *

----

CLASS zl_lcl_car DEFINITION FINAL

INHERITING FROM zl_lcl_vehicle.

PUBLIC SECTION.

METHODS: set_make REDEFINITION,

get_make REDEFINITION,

FINAL method 'get_n_o_veh_type' of superclass can't be redefined *
get_n_o_veh_type REDEFINITION,
All the methods of a FINAL class are implicitly FINAL. So there is *
no need to repeat the FINAL addition in these methods. *

display_car_availability.

PRIVATE SECTION.

DATA: gv_make TYPE string, " Vehicle make

gv_model TYPE string. " Type or model

ENDCLASS. "zl_lcl_car DEFINITION

&----

*& Class (Implementation) zl_lcl_car

&----

Implementation of Subclass

----

CLASS zl_lcl_car IMPLEMENTATION.

METHOD set_make.

*This method originally defined in the superclass is redefined in this *

*subclass. While redefining the method retains the same name and *

*interface, but has a new implementation. *

IF im_make IS NOT INITIAL

AND im_model IS NOT INITIAL.

CONCATENATE im_make '#' INTO gv_make.

CONCATENATE im_model '#' INTO gv_model.

ENDIF.

ENDMETHOD. "set_make

METHOD get_make.

*This method originally defined in the superclass is redefined in this *

*subclass. While redefining the method retains the same name and *

*interface, but has a new implementation. *

CONCATENATE gv_make '!' INTO ex_make.

CONCATENATE gv_model '!' INTO ex_model.

ENDMETHOD. "get_make

METHOD display_car_availability.

WRITE / 'Car of this make and model is available. '.

ENDMETHOD. "display_car_availability

ENDCLASS. "zl_lcl_car

Declaring a reference variable with reference to the subclass

DATA z_car TYPE REF TO zl_lcl_car.

DATA : gv_make TYPE string,

gv_model TYPE string,

gv_veh_type_cnt TYPE i.

START-OF-SELECTION.

Create instance of the vehicle class

CREATE OBJECT z_car.

z_car->set_make( EXPORTING im_make = 'HYUNDAI'

im_model = 'SANTRO' ).

z_car->get_make( IMPORTING ex_make = gv_make

ex_model = gv_model ).

z_car->get_n_o_veh_type( IMPORTING ex_veh_typ = gv_veh_type_cnt ).

WRITE: / 'Vehicle Code :', gv_veh_type_cnt,

/ 'Make :', gv_make,

/ 'Model :', gv_model.

z_car->display_car_availability( ).

<b>Award points if useful.</b>

Regards

Indrajit

Re: final

Former Member — Fri, 06 Jul 2007 10:41:17 GMT

Hi Sandeep,

Final –

Final classes cannot have subclasses.

They conclude an inheritance tree.

A final method cannot be redefined in a subclass.

All methods in final classes are automatically final.

Reward Points If useful.