Polymorphism | 39In comparing Example 1-33 with Example 1-34, both theproductDescribe( )and
productPrice( )methods look pretty much the same other than the literal used in the
returnstatement in theproductDescribe( ). In fact, by adding a string parameter to
theproductDescribe( )method, we could make them identical. However, the point
of this application is to demonstrate polymorphism, and so creating different forms
of the methods is intentional.
You can see the practicality of polymorphism by comparing theproductDisplay( )
methods in the two examples. Example 1-33 is set up to play a video and
Example 1-34 a sound. However, note that the identical signatures are maintained in
both examples.
}
}
}
Example 1-34. MP3Player.as
package
{
import flash.media.Sound;
import flash.media.SoundChannel;
import flash.net.URLRequest;
public class MP3Player implements IBiz
{
private var sound:Sound;
private var playChannel:SoundChannel;
private var doPlay:URLRequest;
private var MP3Price:Number;
public function productDescribe( ):String
{
return "MP3Player with 1 Terabyte of Memory";
}
public function productPrice(price:Number):String
{
MP3Price=price;
return "$" + MP3Price + "\n";
}
public function productDisplay(song:String):void
{
sound=new Sound( );
playChannel=new SoundChannel( );
doPlay=new URLRequest(song);
sound.load(doPlay);
playChannel=sound.play( );
}
}
}
Example 1-33. Plasma.as (continued)