Introduction to OOP Chapter 8: Inheritance and Substitution: next previous audio real text

Interfaces and Abstract Classes

An interface is similar to a class, but does not provide any implementation. A child class must override all methods. A middle ground is an abstract class. Here some methods are defined, and some (abstract methods) are undefined. A child class must fill in the definition for abstract methods:
abstract class Window {
	abstract public void paint (); // child class must redefine
An interface is like an abstract class in which all methods are abstract. In C++ an abstract method is called a pure virtual method.
Intro OOP, Chapter 8, Slide 14