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

interface. You’ll need an MP3 file named bongo.mp3 (use any handy MP3 file) saved
in the same folder as the MakeSound.as file.
Example 1-20. MakeSound.as
package
{
import flash.display.Sprite;
public class MakeSound extends Sprite
{
private var guitar:BandFace;
private var bongo:BandFace;
}
}
public function MakeSound( ):void
{
guitar=new Guitar( );
guitar.playInstrument("Gibson");
}
bongo=new Bongo( );
bongo.playInstrument("bongo.mp3");
Note that both instances, guitar and bongo, are typed to the supertype, BandFace, and
not to either the Guitar or the Bongo classes. This practice follows the first principle
of reusable object-oriented design: Program to an interface, not an implementation.
The purpose of doing so is to maintain flexibility and reusability. This principle will
be fully explored elsewhere in this chapter and in Chapter 8, but for now, just note
that fact.
A word about the interface and abstract class naming conventions
used in this book: with the focal point of this book on object-oriented
programming and design patterns, we use naming conventions that
best reflect and clarify the structure of the different design patterns. As
a result, we don’t always follow some of the naming conventions. One
convention is to name interfaces beginning with a capital I. So following
that convention, the BandFace interface would have been named
IBandFace. Where using the I does not interfere with clarifying a
design pattern structure, we use it, but where we have several interfaces
in a design pattern, often we forego that convention. Another
convention is to name abstract classes using Abstract+ Something. So,
AbstractHorses would be a name for a class you’d otherwise name
Horses. Again, our focus on revealing structure supersedes using these
conventions. We differentiate abstract from concrete classes using
comments in the code. Throughout the book, however, we attempt to
be as clear as possible in naming the different classes. You may want
to adopt some of these more common conventions, once you better
understand them, to aid in keeping your code clear.
30 | Chapter 1: Object-Oriented Programming, Design Patterns, and ActionScript 3.0