ActionScript for Flash MX: The Definitive Guide, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

292

|

Chapter 12: Objects and Classes

When defining a property that will hold a constant value, it is also perfectly legiti-

mate to use the class’s

prototype property, as follows:

function Square ( ) {

statements

}

Square.prototype.numSides = 4;

However, this approach demands that numSides be accessed through an instance of

Square, not through the Square class directly. If you want to use a property without

first creating an instance of a class, you should make that property static.

Sometimes, static properties and methods are used to package a series of related con-

stants and functions into a class that will never be instantiated. In ActionScript, this

is normally achieved by adding properties and methods to a generic instance of the

Object class. For example, the Math, Key, Mouse, and Stage objects are implemented

in this manner.

For the benefit of Java programmers, Table 12-1 outlines the rough equivalencies

between Java and ActionScript methods and properties.

Inheritance: Superclasses and Subclasses

One of the crucial features of classes in advanced object-oriented programming is

their ability to inherit properties and methods. That is, an entire class can adopt the

properties and methods of another class and add its own specialized features. The

class that borrows the properties and ...