This commit broke the validator messages for classes extending MaximimumValidator, MinimumValidator, and RangeValidator.
To reproduce, go to wicket-examples/dates and submit an invalid "hours" value (e.g. -2) in the "Example using DateTimeField".
Prior to this, the resource key was set to a hard coded value. Now it is Classes.simpleName(getClass()). DateTimeField uses a custom RangeValidator subclass (HoursValidator) so it can't find the resource key anymore.
I think it would be prudent to use the previously hard coded key values in the new resourceKey() method so subclasses not wanting to override the default message key can still use it.