ActionScript Syntax for Flex Applications - Variables and Properties continued
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In addition to thepublic,private,protected, andinternalmodifiers, you can also combine these modifiers with thestaticmodifier. Thestatic modifier says that the property is directly accessible from the class rather than from instances. Static modifiers are used for many purposes, including design patterns such as the Singleton pattern. The following example adds a staticprivateproperty called
_instanceof typeExample:
package com.example {
import flash.net.URLLoader;
import flash.net.URLRequest;
public class Example {
private var _loader:URLLoader;
static private var _instance:Example;
}
}
A concept related to properties is that of the constant. A constant is a container for data, much like a variable/property except that once it has a value, you cannot change the value (hence the name, constant). You’ve likely seen constants in the Flash Player and Flex framework API. A few examples of constants areEvent.COMPLETE,MouseEvent.CLICK,TimerEvent.TIMER, andMath.PI. Although not a requirement, most constants are declared asstatic, and most are also declared aspublic(unlike properties, constants aren’t part of a class’s state and can therefore be declaredpublic). To declare a constant, use theconst keyword rather thanvar. By convention, constant names are all uppercase, as shown here:
package com.example{
import flash.net.URLLoader;
import flash.net.URLRequest;
public class Example {
private var _loader:URLLoader;
static private var _instance:Example;
static public const TEST:String = "test constant";
}
}
Please check back next week for the continuation of this article.
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 This article is excerpted from chapter four of the book Programming Flex 2, written by Chafic Kazoun and Joey Lott (O'Reilly, 2007; ISBN: 059652689X). Check it out today at your favorite bookstore. Buy this book now.
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