Ans. Interfaces is being used for HAS-A Concept. While we will see that for an object you need to keep has concept (like a building has 10 rooms, 20 doors, 60 windows), you need to implement interface.
Also interfaces is being used for multiple inheritance concept.

For more details please refer:
http://docs.oracle.com/javase/tutorial/java/concepts/interface.html

Posted on Aug 02, 2014 by Ranveer