1、定义接口
INTERFACE intf [PUBLIC].
[components]
ENDINTERFACE.
2、注意点：
2.1、接口中所定义的所有东西默认都是公共的，所以不用也不能写PUBLIC SECTION。
2.2、只有在接口中定义的常量（CONSTANTS）才可以使用 VALUE 选项来初始化，而DATA、CLASS-DATA定义的变量是不能初始化
2.3、接口定义中也只能包含成员声明部分，而具体的实现将在具体类中进行
2.4、如果要实现某个接口，则在类的公共声明PUBLIC SECTION部分进行实现，其余部分不行
3、定义一个接口 MediaPlayer，表示家庭影院的一个设备。MediaPlayer 中包含 play()，stop()， open()三个方法，分别表示播放、停止和开仓功能。
MediaPlayer 有三个实现类，分别为： DVDPlayer，表示 DVD 播放器； CDPlayer，表示 CD 播放器；TapePlayer，表示录音机（播放磁带）。
INTERFACE mediaplayer. CONSTANTS pi TYPE f VALUE '3.1415926'. CLASS-DATA dd type f . METHODS: play,stop,open. ENDINTERFACE. CLASS dvdplayer DEFINITION. PUBLIC SECTION. INTERFACES mediaplayer. ENDCLASS. CLASS dvdplayer IMPLEMENTATION. METHOD mediaplayer~play. WRITE / 'dvd is play'. ENDMETHOD. METHOD mediaplayer~stop. WRITE / 'dvd is stop'. ENDMETHOD. METHOD mediaplayer~open. WRITE / 'dvd is open'. ENDMETHOD. ENDCLASS. CLASS cdplayer DEFINITION. PUBLIC SECTION. INTERFACES mediaplayer. ENDCLASS. CLASS cdplayer IMPLEMENTATION. METHOD mediaplayer~play. WRITE / 'cd is play'. ENDMETHOD. METHOD mediaplayer~stop. WRITE / 'cd is stop'. ENDMETHOD. METHOD mediaplayer~open. WRITE / 'cd is open'. ENDMETHOD. ENDCLASS. CLASS tapeplayer DEFINITION. PUBLIC SECTION. INTERFACES mediaplayer. ENDCLASS. CLASS tapeplayer IMPLEMENTATION. METHOD mediaplayer~play. WRITE / 'tape is play'. ENDMETHOD. METHOD mediaplayer~stop. WRITE / 'tape is stop'. ENDMETHOD. METHOD mediaplayer~open. WRITE / 'tape is open'. ENDMETHOD. ENDCLASS. *声明对象 DATA: dvd TYPE REF TO dvdplayer, cd TYPE REF TO cdplayer, tape TYPE REF TO tapeplayer. START-OF-SELECTION. CREATE OBJECT dvd. CREATE OBJECT cd. CREATE OBJECT tape. CALL METHOD dvd->mediaplayer~play. CALL METHOD cd->mediaplayer~stop. CALL METHOD tape->mediaplayer~open. write / dvd->mediaplayer~pi. write / dvd->mediaplayer~dd. dvd->mediaplayer~dd = 1. write / dvd->mediaplayer~dd.