Events: Introductory Example (SAP Library - BC

Events: Introductory Example

The following simple example shows the principle of events within ABAP Objects. It is based on the Simple Introduction to Classes. An event critical_value is declared and triggered in class counter.

REPORT demo_class_counter_event.
CLASS counter DEFINITION.
  PUBLIC SECTION.
    METHODS increment_counter.
    EVENTS  critical_value EXPORTING value(excess) TYPE i.
  PRIVATE SECTION.
    DATA: count     TYPE i,
          threshold TYPE i VALUE 10.
ENDCLASS.
CLASS counter IMPLEMENTATION.
  METHOD increment_counter.
    DATA diff TYPE i.
    ADD 1 TO count.
    IF count > threshold.
      diff = count - threshold.
      RAISE EVENT critical_value EXPORTING excess = diff.
    ENDIF.
  ENDMETHOD.
ENDCLASS.
CLASS handler DEFINITION.
  PUBLIC SECTION.
    METHODS handle_excess
            FOR EVENT critical_value OF counter
            IMPORTING excess.
ENDCLASS.
CLASS handler IMPLEMENTATION.
  METHOD handle_excess.
    WRITE: / 'Excess is', excess.
  ENDMETHOD.
ENDCLASS.
DATA: r1 TYPE REF TO counter,
      h1 TYPE REF TO handler.
START-OF-SELECTION.
  CREATE OBJECT: r1, h1.
  SET HANDLER h1->handle_excess FOR ALL INSTANCES.
  DO 20 TIMES.
    CALL METHOD r1->increment_counter.
  ENDDO.

The class COUNTER implements a counter. It triggers the event CRITICAL_VALUE when a threshold value is exceeded, and displays the difference. HANDLER can handle the exception in COUNTER. At runtime, the handler is registered for all reference variables that point to the object.