Why interface over abstract
------------------------------------Interface can fill gap of multiple inheritance. One can
implement from more than one interface. Not same with Abstract. One can inherit
from only one abstract class.
Interfaces are useful when you do not want classes to inherit from unrelated classes just to get the required functionality. For example, let bird be a class with a method fly(). It will be ridiculous for an aeroplane to inherit from bird class just because it has the fly() method. Rather the fly() method should be defined as an interface and both bird and aeroplane should implement that interface.
