Invoked when there was data change for the supplied path, which was used
to register this listener.
This method may be also invoked during registration of the listener if
there is any pre-existing data in the conceptual data tree for supplied
path. This initial event will contain all pre-existing data as created.
A data change event may be triggered spuriously, e.g. such that data before
and after compare as equal. Implementations of this interface are expected
to recover from such events. Event producers are expected to exert reasonable
effort to suppress such events.
In other words, it is completely acceptable to observe
a
DataObjectModification, while the state observed before and
after- data items compare as equal.