ActionScript 3 - Hello Application

Files required...
Greeter.as
Hello.mxml

Compile these two files into...
Hello.swf

Code for Greeter.as
package
{
   public class Greeter
   {
      /* Defines the names that should receive a proper greeting. */
      public static var validNames:Array = ["Dave", "Scratch", "Leigh"];
      /* Builds a greeting string using the given name. */
      public function sayHello(userName:String = ""):String
      {
         var greeting:String;
         if (userName == "")
         {
            greeting = "Hello. Please type your user name, and then press the Enter key.";
         }
         else if (validName(userName))
         {
          greeting = "Hello, " + userName + ".";
         }
         else
         {
         greeting = "Sorry " + userName + ", you are not on the list.";
         }
         return greeting;
      }

      /* Checks whether a name is in the validNames list. */
      public static function validName(inputName:String = ""):Boolean
      {
         if (validNames.indexOf(inputName) > -1)
         {
             return true;
         }
         else
         {
            return false;
         }
      }
   }
}

Code for Hello.mxml

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" xmlns="*"
layout="vertical"
creationComplete = "initApp()" >

<mx:Script>
<![CDATA[
private var myGreeter:Greeter = new Greeter();

      public function initApp():void
      {
         // says hello at the start, and asks for the user's name
         mainTxt.text = myGreeter.sayHello();
      }

]]>
</mx:Script>

<mx:TextArea id = "mainTxt" width="400" backgroundColor="#DDDDDD" editable="false" />
   <mx:HBox width="400">
   <mx:Label text="User Name:"/>
   <mx:TextInput id="userNameTxt" width="100%" enter="mainTxt.text = myGreeter.sayHello(userNameTxt.text);" />
</mx:HBox>

</mx:Application>