MACROMEDIA FLASH MX 2004 - ACTIONSCRIPT, Reference Manual

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CHAPTER 9
Creating Classes with ActionScript 2.0
ActionScript 2.0 is a restructuring of the ActionScript language that provides several powerful
new programming features found in other programming languages, such as Java. ActionScript 2.0
encourages program structures that are reusable, scalable, robust, and maintainable. It also
decreases development time by providing users with thorough coding assistance and debugging
information. ActionScript 2.0 conforms to existing standards and is based on the ECMAScript 4
proposal (
www.mozilla.org/js/language/es4/ ). ActionScript 2.0 is available in Macromedia Flash
MX 2004 and Macromedia Flash MX Professional 2004.
The features of ActionScript 2.0 are described below.
Familiar object-oriented programming (OOP) model
The primary feature of
ActionScript 2.0 is a familiar model for creating object-oriented programs. ActionScript 2.0
introduces several new object-oriented concepts and keywords such as
class , interface , and packages
that will be familiar to you if you’ve ever programmed with Java.
The OOP model provided by ActionScript 2.0 is a “syntactic formalization” of the prototype
chaining method used in previous versions of Macromedia Flash to create objects and
establish inheritance.
Strict data typing ActionScript 2.0 also lets you explicitly specify data types for variables,
function parameters, and function return types. For example, the following code declares a
variable named
userName
of type String (a built-in ActionScript data type, or class).
var userName:String = "";
Compiler warnings and errors
The above two features enable the authoring tool and compiler
to provide compiler warnings and error messages that help you find bugs in your applications
faster than was previously possible in Flash.
Caution: If you plan to use ActionScript 2.0 syntax, ensure that the Publish settings for the FLA file
specify ActionScript 2.0. This is the default for files created in Flash MX 2004. However, if you open
an older FLA file that uses ActionScript 1 and begin rewriting it in ActionScript 2.0, change the
Publish Settings of the FLA file to ActionScript 2.0. If you don’t do so, your FLA file will not compile
correctly, but no errors will be generated.