Object Oriented Programming Through Java by Pearson

Java Features 2.7

methods with only names and no implementation details. In Java, these types of classes are

called interfaces and methods are called abstract method. An abstract method is a method

that is declared but not defined. It is declared with the keyword abstract, and has a header like

any other method, but ends with a semicolon instead of a method body.

An abstract class is one that contains one or more abstract methods; it must itself be declared

with the abstract keyword. A class may be declared abstract even if it does not contain any

abstract methods. A non-abstract class is sometimes called a concrete class. An abstract class

cannot be instantiated because it has no solid methods. We will derive classes like Circle and

Square ...