Re: oops-methodoverriding

Former Member — Tue, 03 Jul 2007 09:30:42 GMT

Hi check this out it may be helpful.

) In overloading, there is a relationship between methods available in the same class whereas in overriding, there is relationship between a superclass method and subclass method.

b) Overloading does not block inheritance from the superclass whereas overriding blocks inheritance from the superclass.

c) In overloading, separate methods share the same name whereas in overriding, subclass method replaces the superclass.

d) Overloading must have different method signatures whereas overriding must have same signature.

CLASS zl_lcl_vehicle DEFINITION.

PUBLIC SECTION.

Signature of method

METHODS: set_make

IMPORTING value(im_make) TYPE string " Pass by value

im_model TYPE string," Pass by reference

ENDCLASS. "zl_lcl_vehicle DEFINITION

CLASS zl_lcl_vehicle IMPLEMENTATION.

Implementation of method.

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

ENDCLASS. "zl_lcl_vehicle

Overloading means changing signature as well as implementation of a method.

Overriding is changing only implementation of method with signature unchanged.

From ABAP perspective, only the CONSTRUCTOR method can be overloaded in a subclass i.e both the signature and implementation can be adapted in subclass.

Any other method can't be overloaded. It can only be redefined/overridden i.e implementation changed with signature unchanged.

Award points if found useful.

Regards,

Rajesh

Re: oops-methodoverriding

Former Member — Wed, 04 Jul 2007 07:39:22 GMT

Hi Sandeep,

Overriding is changing method implementation with signature unchanged.

Overloading is changing signature as well as implementation.

In ABAP, overlaoding is not possible for methods with one exception. Only the constructor method can be overlaoded in a subclass during inheritance.

For all other methods, only overriding is possible.

Check out the following programs.

Method overriding

&----

*& Class (Definiton) zl_lcl_vehicle

&----

Definition of the Superclass

----

CLASS zl_lcl_vehicle DEFINITION.

PUBLIC SECTION.

Visible to all

METHODS: set_make IMPORTING im_make TYPE string

im_model TYPE string,

get_make EXPORTING ex_make TYPE string

ex_model TYPE string.

PROTECTED SECTION.

Visible within class and all subclasses

DATA gv_n_o_veh TYPE i.

PRIVATE SECTION.

Only visible within the class

DATA: gv_make TYPE string, " Vehicle make

gv_model TYPE string. " Type or model

ENDCLASS. "zl_lcl_vehicle DEFINITION

&----

*& Class (Implementation) zl_lcl_vehicle

&----

Implementation of the 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

ENDCLASS. "zl_lcl_vehicle

&----

*& Class (Definiton) zl_lcl_car

&----

Definition of the Subclass

----

CLASS zl_lcl_car DEFINITION INHERITING FROM zl_lcl_vehicle.

PUBLIC SECTION.

METHODS: set_vehtype IMPORTING im_vehtype TYPE string

im_n_o_veh TYPE i,

get_vehtype EXPORTING ex_vehtype TYPE string

ex_n_o_veh TYPE i,

Begin of IC240107
To change the implementation of a superclass instance method in *
subclass, without changing the method signature, the method must be *
defined in subclass with REDIFINITION addition. There is no need to *
define the method parameters and exceptions again. *
Redifinition is not possible for private methods. *
Redefining methods introduces POLYMORPHISM in classes. *
REDEFINITION addition must be used to implement an abstract method *
of a superclass in a subclass. However a final method in a *
superclass can't be redefined in superclass. *
The constructors of a class are always final and cannot be redefined.*

get_make REDEFINITION.

End of IC240107

PRIVATE SECTION.

DATA gv_vehtype TYPE string.

ENDCLASS. "zl_lcl_car DEFINITION

&----

*& Class (Implementation) zl_lcl_car

&----

Implementation of the Subclass

----

CLASS zl_lcl_car IMPLEMENTATION.

METHOD set_vehtype.

IF im_vehtype IS NOT INITIAL.

gv_vehtype = im_vehtype.

Protected component of superclass can be directly accessed in subclass. *
The same applies for public components, private compenets of superclass *
have to be accessed using public or protected methods of superclass. *

gv_n_o_veh = im_n_o_veh.

ENDIF.

ENDMETHOD. "set_vehtype

METHOD get_vehtype.

ex_vehtype = gv_vehtype.

ex_n_o_veh = gv_n_o_veh.

ENDMETHOD. "get_vehtype

Begin of IC240107
When REDIFINITION addition is used with any method in subclass *
definition a new implementation part must be specified for the *
inherited method. *

METHOD get_make.

To access the superclass method from the redefined method, use the *
pseudo-reference SUPER *

super->get_make( IMPORTING ex_make = ex_make

ex_model = ex_model ).

ENDMETHOD. "get_make

End of IC240107

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_vehtype TYPE string,

gv_n_o_veh TYPE i.

START-OF-SELECTION.

Creating an instance of the subclass

CREATE OBJECT: z_car.

Accessing the public methods of superclass using subclass reference

z_car->set_make( EXPORTING im_make = 'MARUTI'

im_model = '800' ).

POLYMORPHISM - There are 2 implementations of the method get_make *
one in superclass and one in subclass. Since the method is *
redefined in subclass, subclass implementation will be executed *
if subclass reference is used. *

z_car->get_make( IMPORTING ex_make = gv_make

ex_model = gv_model ).

Accessing the methods of subclass using subclass reference

z_car->set_vehtype( EXPORTING im_vehtype = 'Car'

im_n_o_veh = '10' ).

z_car->get_vehtype( IMPORTING ex_vehtype = gv_vehtype

ex_n_o_veh = gv_n_o_veh ).

WRITE: / 'Vehicle type :', gv_vehtype,

/ 'Make :', gv_make,

/ 'Model :', gv_model,

/ 'No of ordered vehicles :', gv_n_o_veh.

Constructor Overlaoding

&----

*& Class (Definiton) zl_lcl_vehicle

&----

Definition of the Superclass

----

CLASS zl_lcl_vehicle DEFINITION.

PUBLIC SECTION.

Visible to all

METHODS: set_make IMPORTING im_make TYPE string

im_model TYPE string,

get_make EXPORTING ex_make TYPE string

ex_model TYPE string,

Begin of IC240107
Superclass Constructor

constructor IMPORTING im_n_o_vehicle TYPE i.

End of IC240107

PROTECTED SECTION.

Visible within class and all subclasses

DATA gv_n_o_veh TYPE i.

PRIVATE SECTION.

Only visible within the class

DATA: gv_make TYPE string, " Vehicle make

gv_model TYPE string. " Type or model

ENDCLASS. "zl_lcl_vehicle DEFINITION

&----

*& Class (Definiton) zl_lcl_vehicle

&----

Definition of the Subclass

----

CLASS zl_lcl_car DEFINITION INHERITING FROM zl_lcl_vehicle.

PUBLIC SECTION.

METHODS: get_vehtype EXPORTING ex_vehtype TYPE string

ex_n_o_veh TYPE i,

Begin of IC240107
Constructor Overloading. Both the signature and implementation of *
method can be adapted in the subclass. *

constructor IMPORTING ims_n_o_vehicle TYPE i

ims_vehtype TYPE string.

End of IC240107

PRIVATE SECTION.

DATA gv_vehtype TYPE string.

ENDCLASS. "zl_lcl_car DEFINITION

&----

*& Class (Implementation) zl_lcl_vehicle

&----

Implementation of the 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

Begin of IC240107
Superclass constructor implementation

METHOD constructor.

gv_n_o_veh = im_n_o_vehicle.

ENDMETHOD. "constructor

End of IC240107

ENDCLASS. "zl_lcl_vehicle

&----

*& Class (Implementation) zl_lcl_car

&----

Implementation of the Subclass

----

CLASS zl_lcl_car IMPLEMENTATION.

METHOD get_vehtype.

ex_vehtype = gv_vehtype.

ex_n_o_veh = gv_n_o_veh.

ENDMETHOD. "get_vehtype

Begin of IC240107
Subclass constructor implementation

METHOD constructor.

If subclass constructor is overloaded, it is mandatory to call
superclass constructor within subclass constructor, because superclass
constructor is meant to be executed when object is created for super
or sub class. If subclass constructor is not overloaded, then the
runtime system will ensure this automatically.
Static constructors in superclass are always executed automatically
before any static constructor in subclass is executed.

Comment out the following and see what happens

super->constructor( EXPORTING im_n_o_vehicle = ims_n_o_vehicle ).

gv_vehtype = ims_vehtype.

ENDMETHOD. "constructor

End of IC240107

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_vehtype TYPE string,

gv_n_o_veh TYPE i.

START-OF-SELECTION.

Creating an instance of the subclass

CREATE OBJECT z_car

Begin of IC240107

EXPORTING ims_vehtype = 'Car'

ims_n_o_vehicle = '10' .

End of IC240107

Accessing the public methods of superclass

z_car->set_make( EXPORTING im_make = 'MARUTI'

im_model = '800' ).

z_car->get_make( IMPORTING ex_make = gv_make

ex_model = gv_model ).

z_car->get_vehtype( IMPORTING ex_vehtype = gv_vehtype

ex_n_o_veh = gv_n_o_veh ).

WRITE: / 'Vehicle type :', gv_vehtype,

/ 'Make :', gv_make,

/ 'Model :', gv_model,

/ 'No of ordered vehicles :', gv_n_o_veh.

Award points if found useful.

Regards

Indrajit

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