ABAP与设计模式之策略模式

 

本文整合自两篇网文，略做加工，以与前篇保持统一风格.

 

原文地址： http://tech.it168.com/a2009/0731/616/000000616596.shtml / http://hi.baidu.com/oabap/item/396ef07827a99a10d0dcb3dd

 

首先介绍策略模式的基本内容
    1. 意图:
    定义一系列算法,把他们一个个的封装起来,并且使他们可以互相替换.本模式可以使得算法可以独立于使用他的客户而变化.
    2. 结构:
        

     3. 适用性:
         1).许多相关的类仅仅是行为有异.
         2).需要使用一个算法的不同变体.
         3).一个类定义了多种行为,并且这些行为在这个类的操作中以多个条件语句的形式出现.
   

    4. 参与者:
        1).Strategy
             定义所支持的算法的公共接口.context使用这个接口来调用某个concrete strategy所定义的算法.
        2).ConcreteStrategy
             以strategy接口实现具体的算法
        3).context
             用一个concretestrategy对象来配置维护一个strategy对象的引用,  可定义一个接口来让strategy访问它的数据
   

    5. 效果
       1).相关算法系列
       2).一个替代继承的方法
        3).消除一系列条件语句
   

    Note:
    对于效果,我想在以后的例子中就会有所体现,现在只是基本的定义以及结构,所以看上去有些晦涩难懂,不过不要着急,慢慢的就能理解了.
    策略模式的例子(UML类图):
   

     程序代码:

    

REPORT  zgary_t014.INCLUDE zgary_t014_define.START-OF-SELECTION.  DATA: grf_mallard_duck TYPE REF TO lcl_mallard_duck.  CREATE OBJECT grf_mallard_duck.  CALL METHOD grf_mallard_duck->performquack.  CALL METHOD grf_mallard_duck->performfly.  CALL METHOD grf_mallard_duck->display.*&---------------------------------------------------------------------**&  Include           ZGARY_T014_DEFINE*&---------------------------------------------------------------------*INTERFACE li_fly_behavior.  METHODS fly.ENDINTERFACE.                    "*----------------------------------------------------------------------**        INTERFACE li_quack_behavior*----------------------------------------------------------------------***----------------------------------------------------------------------*INTERFACE li_quack_behavior.  METHODS quack.ENDINTERFACE.                    "*----------------------------------------------------------------------**        CLASS lcl_Duck DEFINITION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_duck DEFINITION ABSTRACT.  PUBLIC SECTION.    METHODS:    performfly,    performquack,    display ABSTRACT.  PROTECTED SECTION.    DATA: fly_behavior    TYPE REF TO li_fly_behavior,    quack_behavior  TYPE REF TO li_quack_behavior.ENDCLASS.                    "lcl_Duck DEFINITION*----------------------------------------------------------------------**        CLASS lcl_fly_with_wings DEFINITION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_fly_with_wings DEFINITION .  PUBLIC SECTION.    INTERFACES: li_fly_behavior.ENDCLASS.                    "lcl_fly_with_wings DEFINITION*----------------------------------------------------------------------**        CLASS lcl_quack DEFINITION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_quack DEFINITION.  PUBLIC SECTION.    INTERFACES: li_quack_behavior.ENDCLASS.                    "lcl_quack DEFINITION*----------------------------------------------------------------------**        CLASS lcl_Squeak DEFINITION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_squeak DEFINITION.  PUBLIC SECTION.    INTERFACES: li_quack_behavior.ENDCLASS.                    "lcl_Squeak DEFINITION*----------------------------------------------------------------------**        CLASS lcl_mute_quack DEFINITION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_mute_quack DEFINITION.  PUBLIC SECTION.    INTERFACES: li_quack_behavior.ENDCLASS.                    "lcl_mute_quack DEFINITION*----------------------------------------------------------------------**        CLASS lcl_mallard_duck DEFINITION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_mallard_duck DEFINITION INHERITING FROM lcl_duck.  PUBLIC SECTION.    METHODS: constructor,    display REDEFINITION.ENDCLASS.                    "lcl_mallard_duck DEFINITION*----------------------------------------------------------------------**        CLASS lcl_duck IMPLEMENTATION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_duck IMPLEMENTATION.  METHOD performfly.    CALL METHOD fly_behavior->fly.  ENDMETHOD.                    "performfly  METHOD performquack.    CALL METHOD quack_behavior->quack.  ENDMETHOD.                    "performquackENDCLASS.                    "lcl_duck IMPLEMENTATION*----------------------------------------------------------------------**        CLASS lcl_fly_with_wings IMPLEMENTATION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_fly_with_wings IMPLEMENTATION.  METHOD li_fly_behavior~fly.    WRITE: / 'I''m flying'.  ENDMETHOD.                    "li_fly_behavior~flyENDCLASS.                    "lcl_fly_with_wings IMPLEMENTATION*----------------------------------------------------------------------**        CLASS lcl_quack IMPLEMENTATION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_quack IMPLEMENTATION.  METHOD li_quack_behavior~quack.    WRITE: / 'quack'.  ENDMETHOD.                    "li_quack_behavior~quackENDCLASS.                    "lcl_quack IMPLEMENTATION*----------------------------------------------------------------------**        CLASS lcl_mute_quack IMPLEMENTATION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_mute_quack IMPLEMENTATION.  METHOD li_quack_behavior~quack.    WRITE: / '<<Silence>>'.  ENDMETHOD.                    "li_quack_behavior~quackENDCLASS.                    "lcl_mute_quack IMPLEMENTATION*----------------------------------------------------------------------**        CLASS lcl_squeak IMPLEMENTATION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_squeak IMPLEMENTATION.  METHOD li_quack_behavior~quack.    WRITE: / 'squeak'.  ENDMETHOD.                    "li_quack_behavior~quackENDCLASS.                    "lcl_squeak IMPLEMENTATION*----------------------------------------------------------------------**        CLASS lcl_mute_quack IMPLEMENTATION*----------------------------------------------------------------------***----------------------------------------------------------------------*CLASS lcl_mallard_duck IMPLEMENTATION.  METHOD constructor.    CALL METHOD super->constructor.    DATA: lrf_quack_behavior TYPE REF TO lcl_quack,    lrf_fly_behavior TYPE REF TO lcl_fly_with_wings.    CREATE OBJECT: lrf_quack_behavior,    lrf_fly_behavior.    quack_behavior = lrf_quack_behavior.    fly_behavior    = lrf_fly_behavior.    CLEAR: lrf_quack_behavior,    lrf_fly_behavior.  ENDMETHOD.                    "constructor  METHOD  display .    WRITE: / 'I''m a real Mallard duck'.  ENDMETHOD.                    "displayENDCLASS.                    "lcl_mute_quack IMPLEMENTATIO

运行结果：

 

注：代码部分来自 http://hi.baidu.com/oabap/item/396ef07827a99a10d0dcb3dd

    策略模式定义了一系列的算法，并将每一个算法封装起来，而且使它们还可以相互替换，参考Headfirst 设计模式一书,使用abap OO实现