Question

What is an abstract class? How is it different from an interface?

Answer 1

One more classic question from Programming Job interviews, it is as old as chuck Norris. An abstract class is a class which can have state, code and implementation, but an interface is a contract which is totally abstract. Since I have answered it many times, I am only giving you the gist here but you should read the article linked to answer to learn this useful concept in much more detail.