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

The product classes are defined as internal (the default class attribute in Action-
Script 3.0). This means that they’re not publicly visible. They can only be called from
within the example package. Now, let’s examine the creator classes.
Creator Classes
Example 2-4 through Example 2-6 show the creator classes. As with the product
classes, all creators belong to the package example. The creator classes are defined as
public, which indicates that they are publicly accessible from outside the package.
The creator class, as indicated by the comments, should behave as an abstract class.
It should be subclassed and not be instantiated. It also defines the factory method
that should behave as an abstract method. Note that the two concrete creator classes
CreatorA and CreatorB extend Creator. They also override and implement the
factoryMethod( ) method, each returning a corresponding product object. In addition,
the factoryMethod( ) declared in the Creator class has to return null to prevent
a compile-time error. It will also throw an IllegalOperationError if called directly.
This is a runtime check to make sure that this method is overridden.
Example 2-4. Creator.as
package example
{
import flash.errors.IllegalOperationError;
}
// ABSTRACT Class (should be subclassed and not instantiated)
public class Creator
{
public function doStuff( ):void
{
var product:IProduct = this.factoryMethod( );
product.manipulate( );
}
}
// ABSTRACT Method (must be overridden in a subclass)
protected function factoryMethod( ):IProduct
{
throw new IllegalOperationError("Abstract method:
must be overridden in a subclass");
return null;
}
Example 2-5. CreatorA.as
package example
{
public class CreatorA extends Creator
{
override protected function factoryMethod( ):IProduct
{
Minimalist Example | 71