Difference between abstract class with all method abstract and interface?

Question

I had an interview where interviewer asked me first what is the difference between abstract class with all the methods abstract and an interface.

I replied that if

Answer 1

I can see such question was already answered. BTW, I would like to share what I consider the best explanation I have read so far.

The bellow text was copied and pasted from Deshmukh, Hanumant. OCP Oracle Certified Professional Java SE 11 Programmer I Exam Fundamentals 1Z0-815: Study guide for passing the OCP Java 11 Developer Certification Part 1 Exam 1Z0-815 (p. 319). Enthuware. Edição do Kindle.

13.2 Distinguish class inheritance from interface inheritance including abstract classes 13.2.1 Difference between Interface and Abstract Class ☝

"What is the difference between an interface and an abstract class" is usually the first question that is asked in a Java "tech-check". While being a simple ice breaker, it also an excellent question to judge a candidate's understanding of OOP. Candidates usually start parroting the technical differences such as an interface cannot have method implementations (which it can, since Java 8), while abstract class can. An interface cannot have static methods (which it can, since Java 8) or instance fields while an abstract class can and so on. All that is correct, but is not really impressive. The fundamental difference between an interface and an abstract class is that an interface defines just the behavior. An interface tells you nothing about the actual object other than how it behaves. An abstract class, on the other hand, defines an object, which in turn, drives the behavior. If you understand this concept everything else about them will fall in place. For example, "movement" is a behavior that is displayed by various kinds of objects such as a Car, a Cat, or a StockPrice. These objects have no commonality except that they move. Saying it the other way round, if you get an object that "moves", you don't get any idea about what kind of an object are you going to deal with. It could be a Car, a Cat, or a StockPrice. If you were to capture this behavior in Java, you would use an interface named Movable with a method named move(). On the other hand, if you talk about Automobile, a picture of an object starts forming in your head immediately. You can sense that an Automobile would be something that would have an engine, would have wheels, and would move. You intuitively know that a StockPrice or a Cat cannot be an Automobile even though they both do move. An abstract class is meant exactly for this purpose, when, once you identify a conceptual object, you do not need to worry about its behavior. The behavior kind of flows automatically. If you create an abstract class named Automobile, you are almost certain that it would have methods such a move, turn, accelerate, or brake. It would have fields for capturing inner details such Engine, Wheels, and Gears. You get all that just by saying the word Automobile. From the above discussion, it should be clear that interfaces and abstract classes are not interchangeable. Even though an abstract class with no non-abstract method looks functionally similar to an interface, both are fundamentally different. If you are capturing a behavior, you must use an interface. If you are capturing a conceptual object, you must use an abstract class.