Why are interfaces preferred to abstract classes?

Question

I recently attended an interview and they asked me the question \"Why Interfaces are preferred over Abstract classes?\"

I tried giving a few answers like:

Answer 1

You define interfaces when you only require that some object implement certain methods but you don't care about its pedigree. So someone can extend an existing class to implement an interface, without affecting the previously existing behavior of that class.

That's why JDBC is all interfaces; you don't really care what classes are used in a JDBC implementation, you only need any JDBC implementation to have the same expected behavior. Internally, the Oracle JDBC driver may be very different from the PostgreSQL driver, but that's irrelevant to you. One may have to inherit from some internal classes that the database developers already had, while another one may be completely developed from scratch, but that's not important to you as long as they both implement the same interfaces so that you can communicate with one or the other without knowing the internal workings of either.