Abstract classes and interfaces in Java serve fundamentally different purposes. Learn the differences between these Java language elements and how to use them in your programs.

Java is not the language it used to be, and that is mostly a good thing. ... Sealed classes, for example, allow the class creator to specify exactly which classes can extend it.

I've got a class in java for a swing application that extends JFrame. This class is pretty much reponsible for everything to do with a certain window in the program.