The annotation @override marks an instance member as overriding a
superclass member with the same name.
The annotation applies to instance methods, getters and setters, and to instance fields, where it means that the implicit getter and setter of the field is marked as overriding, but the field itself is not.
The intent of the @override notation is to catch situations where a
superclass renames a member, and an independent subclass which used to
override the member, could silently continue working using the
superclass implementation.
The editor, or a similar tool aimed at the programmer, may report if no declaration of an annotated member is inherited by the class from either a superclass or an interface.
Use the @override annotation judiciously and only for methods where
the superclass is not under the programmer's control, the superclass is in a
different library or package, and it is not considered stable.
In any case, the use of @override is optional.
For example, the annotation is intentionally not used in the Dart platform libraries, since they only depend on themselves.