Interface Implementation and Class Inheritance

Short note:
If superclass implements some interface and is extended by some subclass, by default the subclass implicitly implemented all methods declared in the interface. Programmers do not need to explicitly specify the implements as in superclass. However, it won't hurt if they do so.

Interface definition:

Superclass definition:

Subclass definition can be either of following two:
(Programmers do not have to override the methods, even explicitly using implements)