Application plug-in interface for handling continuous query events after
they occur. The listener has two methods, one that is called when there
is an event satisfied by the CQ and the other called when there is an
error during CQ processing.
This method is invoked when an event is occurred on the region
that satisfied the query condition of this CQ.
This event does not contain an error.
If CQ is executed using ExecuteWithInitialResults the returned
result may already include the changes with respect to this event.
This could arise when updates are happening on the region while
CQ registration is in progress. The CQ does not block any region
operation as it could affect the performance of region operation.
Its up to the application to synchronize between the region
operation and CQ registration to avoid duplicate event being
This method is invoked when there is an error during CQ processing.
The error can appear while applying query condition on the event.
e.g if the event doesn't has attributes as specified in the CQ query.
This event does contain an error. The newValue may or may not be
available, and will be null if not available.