ActionScript for Flash MX: The Definitive Guide, Second Edition

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

Classes and Object-Oriented Programming

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robbers run away from the cops, and the innocent bystanders move randomly, con-

fused and frightened. In the code for this game, suppose we create an object class to

represent each category of person:

function Cop () { ... }

function Robber () { ... }

function Bystander () { ... }

In addition, we create a superclass, Person, from which the classes Cop, Robber, and

Bystander all inherit:

function Person () { ... }

Cop.prototype = new Person();

Robber.prototype = new Person();

Bystander.prototype = new Person();

On each frame of the Flash movie, every person on the screen should move accord-

ing to the rules for his class. To make this happen, we define a move() method on

every object (the move() method is customized for each class):

Person.prototype.move = function () { ... default move behavior ... }

Cop.prototype.move = function () { ... move to chase robber ... }

Robber.prototype.move = function () { ... move to run away from cop ... }

Bystander.prototype.move = function () { ... confused, move randomly ... }

On each frame of the Flash movie, we want every person on the screen to move. To

manage all the people, we create a master array of Person objects. Here’s an example

of how to populate the

persons array:

// Create our cops

var cop1 = new Cop(); ...