Called immediately before the first call to createKeys(). Override
to set up listening for changes, allocating expensive-to-create
protected void removeNotify()
Called when this child factory is no longer in memory.
Does nothing by default; override if you need notification when not in use anymore.
Note that this is usually not the best place for unregistering listeners, etc.,
as listeners usually keep the child factory in memory, preventing it from being collected, thus preventing
this method to be called in the first place.