Yes, it is mandatory to implement all the methods in a class that implements an interface unless and until that class is an Abstract class.
Let's Make it Simple,
You have two choices:
- implement every method required by the interface
or
- declare the missing methods abstract in your class. This forces you
to declare your class abstract and, as a result, forces you to
subclass the class (and implement the missing methods) before you
can create any objects.