Java™ How To Program (Early Objects), Tenth Edition

Interfaces vs. Abstract Classes

An interface is often used in place of an abstract class when there’s no default implementation to inherit—that is, no fields and no default method implementations. Like public abstract classes, interfaces are typically public types. Like a public class, a public interface must be declared in a file with the same name as the interface and the .java filename extension.

Software Engineering Observation 10.7

Many developers feel that interfaces are an even more important modeling technology than classes, especially with the new interface enhancements in Java SE 8 (see Section 10.10).