ABAP_to_the_Future

Designing Exception Classes 7.2
* Code to do assorted operation type activities
mo_monster->add_new_head( ).
CATCH zcx_power_failure.
mo_candle->light( ).
CLEANUP.
mo_monster->reattach_old_head( ).
ENDTRY.
ENDMETHOD. "Head Swap Operation
Listing 7.5 Head Swap Operations
Looking at the code, you would expect that the CLEANUP code would reattach the
old head before moving on to the CATCH code and lighting the candle. However,
that’s not what happens. If the ZCX_POWER_FAILURE exception is raised in between
removing the current head and attaching a new head, then the CLEANUP code is
ignored. This means that the candle is lit, but the monster is left without a head.
Not good!
This is because the CLEANUP block is only called if the exception is propagated outside
of the current routine (here, HEAD_SWAP_OPERATION) and handled in another
routine. In this example, the ZCX_POWER_FAILURE exception is handled inside the
routine in which the except ion is raised, and so the CLEANUP block is not called.
One way to get around this problem is to add some code to the end of the routine
(outside the TRY/CATCH block) to test for data being in an inconsistent state (e.g.,
monster with no head) and correct the situation. This is shown in Listing 7.6.
CATCH zcx_power_failure.
mo_candle->light( ).
CLEANUP.
"In case an exception is raised which is
"not caught inside this routine
mo_monster->reattach_old_head( ).
ENDTRY.
"In case an exception is caught within this
"routine before the new head is attached
IF mo_monster->number_of_heads = 0.
mo_monster->reattach_old_head( ).
ENDIF.
ENDMETHOD."Head Swap Operation
Listing 7.6 Making 100% Sure a Method Cleans Up After an Exception
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