EventDispatcherってなんぞ？

/**
 * Copyright ug24k8 ( http://wonderfl.net/user/ug24k8 )
 * MIT License ( http://www.opensource.org/licenses/mit-license.php )
 * Downloaded from: http://wonderfl.net/c/1n6M
 */

package
{
	import com.bit101.components.*;
	import flash.display.*;
	import flash.text.*;
	import flash.events.Event;

   [SWF(width="400", height="300",
   			backgroundColor="0xffcfcf", frameRate="12")]
	public class EdispatchTest extends Sprite
	{
		private var btn_:PushButton;

		public function EdispatchTest():void
		{
			btn_ = new PushButton(stage, 10, 20, "Test");
			var text:TextField = new TextField();
			text.type = TextFieldType.DYNAMIC;
			text.x = 10;
			text.y = 80;
                        text.border = true;

			addChild(text);

			var e:EventDispatchTest = new EventDispatchTest(btn_);
			e.addEventListener(EventDispatchTest.PUSH, onPushHandler);

			function onPushHandler(e:Event):void{
				text.text = "ok!";
			}
		}
	}
}


import com.bit101.components.*;
import flash.events.*;
import flash.display.*;

class EventDispatchTest extends EventDispatcher {
	public static const PUSH:String = "push_btn";
	private var btn_:PushButton;

	public function EventDispatchTest(btn:PushButton):void {
		btn_ = btn;
		init();
	}

	private function init():void {
		btn_.addEventListener(MouseEvent.MOUSE_DOWN, onMouseDownHandler);
	}

	private function onMouseDownHandler(e:MouseEvent):void {
		dispatchEvent(new Event(PUSH));
	}
}