5. 方法

方法参数传递:
REPORT z_mehtod_para.
*---------------------------------------------------------------------*
*       CLASS vehicle DEFINITION
*---------------------------------------------------------------------*
*       ........                                                      *
*---------------------------------------------------------------------*
CLASS vehicle DEFINITION.
  PUBLIC SECTION.
    METHODS: accelerate IMPORTING rate TYPE i,
             show_speed.
  PRIVATE SECTION.
    DATA speed TYPE i VALUE 0.
ENDCLASS.
*---------------------------------------------------------------------*
*       CLASS vehicle IMPLEMENTATION
*---------------------------------------------------------------------*
*       ........                                                      *
*---------------------------------------------------------------------*
CLASS vehicle IMPLEMENTATION.
  METHOD accelerate.
    speed = speed + rate.
  ENDMETHOD.
  METHOD show_speed.
    WRITE: / 'Speed:',speed.
  ENDMETHOD.
ENDCLASS.

DATA o_vehicle TYPE REF TO vehicle.

START-OF-SELECTION.
  CREATE OBJECT o_vehicle.
  CALL METHOD o_vehicle->accelerate EXPORTING rate = 2.
  CALL METHOD o_vehicle->accelerate EXPORTING rate = 2.
  CALL METHOD o_vehicle->show_speed.
该示例输出如下:
    4
方法还可以进行动态调用,即通过变量对方法进行指定,例如下列语句
  meth = acclerate.
  call method o_vehicle->(meth).

函数方法:
REPORT z_funtional_method.

*---------------------------------------------------------------------*
*       CLASS circle DEFINITION
*---------------------------------------------------------------------*
*       ........                                                      *
*---------------------------------------------------------------------*
CLASS circle DEFINITION.
  PUBLIC SECTION.
    METHODS get_area IMPORTING value(i_radius) TYPE i
                     RETURNING value(r_size)   TYPE f.
  PRIVATE SECTION.
    CONSTANTS pi TYPE f VALUE '3.14159265'.
ENDCLASS.
*---------------------------------------------------------------------*
*       CLASS circle IMPLEMENTATION
*---------------------------------------------------------------------*
*       ........                                                      *
*---------------------------------------------------------------------*
CLASS circle IMPLEMENTATION.
  METHOD get_area.
    r_size = i_radius ** 2 * pi.
  ENDMETHOD.
ENDCLASS.

PARAMETERS radius TYPE i.
DATA: o_circle TYPE REF TO circle,
      area TYPE f.

START-OF-SELECTION.
  CREATE OBJECT o_circle.
  CALL METHOD o_circle->get_area
              EXPORTING i_radius = radius
              RECEIVING r_size = area.
  WRITE: / area.
  area = o_circle->get_area( radius ).
  WRITE: / area.

构造方法和析构方法
1. 构造方法
   构造方法是运行时环境自动调用的一种方法,用于为对象设定一个初始化状态,不能在程序运行过程中由程序代码调用.与其他方法类似构造方法也存在静态和实例两种形式.构造方法不一定需要在类中定

义,系统通常会自动生成一个默认的构造方法,将对象状态设置为初始值.
构造方法中不包含任何形式的输出参数,其功能只是定义对象状态,而不是对其进行改变.构造方法在create object语句中被调用,因此根据实例构造方法的定义,该语句本身也可以包含输出参数exporting和

返回值exception选项.如果在对象创建过程中出现异常,则对象被删除,引用变量设为初始值.
    类构造方法属于静态方法,只能在程序中被调用一次,即第一次使用该类时调用,该方法也必须在公有部分声明,其名称必须为class_constructor.
    class-methods class_constructor.
    类构造方法不包含接口,而且在其中只能访问类的静态属性.
构造方法:
REPORT z_method_constructor.
*---------------------------------------------------------------------*
*       CLASS vehicle DEFINITION
*---------------------------------------------------------------------*
*       ........                                                      *
*---------------------------------------------------------------------*
CLASS vehicle DEFINITION.
  PUBLIC SECTION.
    METHODS: accelerate IMPORTING rate TYPE i,
             constructor IMPORTING i_speed TYPE i,
             show_speed.
  PRIVATE SECTION.
    DATA speed TYPE i VALUE 0.
ENDCLASS.
*---------------------------------------------------------------------*
*       CLASS vehicle IMPLEMENTATION
*---------------------------------------------------------------------*
*       ........                                                      *
*---------------------------------------------------------------------*
CLASS vehicle IMPLEMENTATION.
  METHOD accelerate.
    speed = speed + rate.
  ENDMETHOD.
  METHOD show_speed.
    WRITE speed.
  ENDMETHOD.
  METHOD constructor.
    speed = i_speed.
  ENDMETHOD.
ENDCLASS.

DATA o_vehicle TYPE REF TO vehicle.

START-OF-SELECTION.
  CREATE OBJECT o_vehicle EXPORTING i_speed = 4.
  CALL METHOD o_vehicle->accelerate EXPORTING rate = 2.
  CALL METHOD o_vehicle->accelerate EXPORTING rate = 2.
  CALL METHOD o_vehicle->show_speed.
该示例输出如下:
     8
在对象创建过程中,通过构造方法传递了一个速度初始值作为其初始状态.
2. 析构方法
   在某些面向对象语言中还存在析构方法的概念,该方法在对象删除过程中被调用,目前ABAP对象中尚未提供该方法的实现形式.