【IT168 技术文章】
在这一节中，我们来实现继承。
背景：有两种飞机，一种是客机，一种是货机。显然他们都属于飞机的一种，所以按照对象抽象，得到父类。对于客机而言，有其特殊的属性即座位的数量，而对于货机，同样有特殊的属性能承载的最大重量。所以，原来父类的显示属性的方法不再适用，我们可以把这个方法定义为抽象方法（c++中的虚函数），也可以保留其共同的实现，在子类中重新定义该方法的实现。
Uml图如下：
*----------------------------------------------------------------------*
* INCLUDE Z_SAMPLE_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.
*------------------------------
* 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.
name = im_name.
planetype = im_planetype.
ENDMETHOD.
METHOD display_attributes.
WRITE:/ 'Name:', name, 'Planetype:', planetype.
ENDMETHOD.
METHOD display_n_o_airplanes.
WRITE: / 'No. planes:', n_o_airplanes.
ENDMETHOD.
ENDCLASS.
*----------------------------------------------------------------------*
* INCLUDE Z_SAMPLE_LCL_PA_AIRPLANE *
*----------------------------------------------------------------------*
*******************************************************************
* 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.
*----------------------------------------------------------------------*
* INCLUDE Z_SAMPLE_LCL_CA_AIRPLANE *
*----------------------------------------------------------------------*
*******************************************************************
* 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
*---------------------------------------------------------------------*
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.
REPORT ZBOBO_OO_011 .
* Super class
Include z_sample_lcl_airplane.
* Sub classes
include z_sample_lcl_pa_airplane.
include z_sample_lcl_ca_airplane.
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.
* INCLUDE Z_SAMPLE_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.
*------------------------------
* 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.
name = im_name.
planetype = im_planetype.
ENDMETHOD.
METHOD display_attributes.
WRITE:/ 'Name:', name, 'Planetype:', planetype.
ENDMETHOD.
METHOD display_n_o_airplanes.
WRITE: / 'No. planes:', n_o_airplanes.
ENDMETHOD.
ENDCLASS.
*----------------------------------------------------------------------*
* INCLUDE Z_SAMPLE_LCL_PA_AIRPLANE *
*----------------------------------------------------------------------*
*******************************************************************
* 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.
*----------------------------------------------------------------------*
* INCLUDE Z_SAMPLE_LCL_CA_AIRPLANE *
*----------------------------------------------------------------------*
*******************************************************************
* 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
*---------------------------------------------------------------------*
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.
REPORT ZBOBO_OO_011 .
* Super class
Include z_sample_lcl_airplane.
* Sub classes
include z_sample_lcl_pa_airplane.
include z_sample_lcl_ca_airplane.
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.
