What is the difference between an abstract class and an interface?

Answer 1

Abstract class should at least contain one abstract method and then it can inherited to initialise. on the other hand interface is not a class, an interface is just an interface made up of only abstract methods, here you don't need to define keyword abstract explicitly.

Answer 2

There are quite a few differences between them, but most importantly

An abstract class is a class that is only partially implemented by the programmer and it is used to implement the same or different behavior among multiple related objects.
and
An interface defines a contract that the implementing classes must fulfill. Its definition consists of the signatures of public members, without any implementing code.

for more detailed answers check this out:

https://stackoverflow.com/questions/1913098/what-is-the-difference-between-an-interface-and-abstract-class