ActionScript 3.0 Design Patterns.pdf - VideoTutorials-bg.com

New Creator Classes: Integrating a Parameterized Factory Method
As with the product classes, we can add a parameterized factory method to our
application without modifying existing code. We won’t change the original
PrintCenter abstract class and its derived classes, LowVolPrintCenter and
HighVolPrintCenter. By letting these be, we don’t break the functionality of the old
interface, and clients using it will continue to function. We will define a new abstract
interface called NewPrintCenter with a parameterized factory method (Example 2-18).
Example 2-18. NewPrintCenter.as
package printcenters
{
import flash.errors.IllegalOperationError;
}
// ABSTRACT Class (should be subclassed and not instantiated)
public class NewPrintCenter
{
}
public function print(fn:String, cKind:uint):void
{
var printjob:IPrintjob = this.createPrintjob(cKind);
printjob.start(fn);
}
// ABSTRACT Method (must be overridden in a subclass)
protected function createPrintjob(cKind:uint):IPrintjob
{
throw new IllegalOperationError("Abstract method:
must be overridden in a subclass");
return null;
}
The factory method createPrintjob( ) takes a parameter of type uint that represents
a kind of print job (color or black and white). In addition, the print( ) method also
takes this as an additional parameter.
We next create two concrete classes (Example 2-19 and Example 2-20) that extend
the NewPrintCenter abstract class for low and high volume printing.
Example 2-19. NewLowVolPrintCenter.as
package printcenters
{
public class NewLowVolPrintCenter extends NewPrintCenter
{
public static const BW :uint = 0;
public static const COLOR :uint = 1;
override protected function createPrintjob(cKind:uint):IPrintjob
Extended Example: Color Printing | 81