Am i correct?

Question

Abstract class - A class that can abstract many thing.
interface - Also a Abstract class,but in invisible way, unrevealed.

Answer 1

They are quite similar, but there are subtle differences between them, for example a class can extend only one abstract class, while it can implement multiple interfaces, an interface can also extend other interfaces (it is not restricted to only one, as well). I believe that interfaces can't change the access modifiers of their variables (which are always public static final) and methods (which are always public abstract) while an abstract class has more freedom here.