Before Java 8, a Java application consisted of at least one class that declared a main() entry-point method. Starting with Java 8, you can accomplish this task with an interface.

An abstract class can declare fields, constructors, and non-abstract methods in addition to or instead of abstract methods. For example, an abstract Vehicle class might declare fields describing ...

A method might accept a specific type and its subclasses, but you want to restrict usage to a select few implementations of your own design. Java's open inheritance model can feel like an open ...