The Decorator Pattern in Action - Decorator Class: Dressing the Dolls
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Example 4-8 is the abstract Decorator class, Dresser, which extends the component class, Model. The major contribution here is simply re-implementing thegetDressed()method with a reference to the inheritedwhatToWearproperty.
Example 4-8. Dresser.as
package
{
//Abstract class
public class Dresser extends Model
{
override public function getDressed():String
{
return whatToWear;
}
}
}
All of the concrete decorators will be subclassed for this class.
The Concrete Classes
Once the two main abstract classes in the Decorator pattern have been established, you’re all set to create the concrete ones. In the previous minimalist Decorator example, you saw the output using the trace() statement. Instead of trace() statements, both the concrete component and decorators need to be formatted for later parsing, so a tilde character (~) has been added as a demarcation point. Because all the strings from both the concrete component and decorators are grouped together into a single large string, the tilde serves as cutting point.
Concrete component class
The concrete component class is the only concrete class that extends directly from the abstract concrete class. All the other classes in this application extend from the abstract decorator class. Using a simple constructor function, Sue(), the class assigns a value to the whatToWear variable. This is enough to identify the class as an instance of the main abstract component class,Model, and to establish a unique name. All decorations use the concrete component as the target for the decorations. Save Example 4-9 asSue.as.
Example 4-9. Sue.as
package
{
public class Sue extends Model
{
public function Sue()
{
whatToWear="~sue";
}
}
}
If you want to create more concrete component classes, all you need to do is create a similar class with a different name and value for thewhatToWear variable. With this structure, you have no limit to the number of new concrete components you can add.
Next: Concrete decorator classes >>
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 This article is excerpted from chapter four of ActionScript 3.0 Design Patterns Object Oriented Programming Techniques, written by William B. Sanders and Chandima Cumaranatunge (O'Reilly, 2007 ISBN: 0596528469). Check it out today at your favorite bookstore. Buy this book now.
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