java interfaces are one of the main reasons people like java (and as other people have said, it's reimplementation in other more modern languages shows how popular and useful they are). They promote code reuse and allow protected variation. Your professors bad explanations aren't a reason to dislike interfaces.
Also how have you not, in a java class, written code that uses polymorphism? That would be the easiest way to understand how useful interfaces are.
Also how have you not, in a java class, written code that uses polymorphism? That would be the easiest way to understand how useful interfaces are.