sampleerrdowncast.as

《Flash AS3殿堂之路》光盘源码 学习ActionScript 3.0

package org.kingda.book.basicoop.polymorphism
{
	import flash.display.Sprite;
	public class SampleErrDowncast extends Sprite
	{
		public function SampleErrDowncast() {
			var base:Base = new Base();
			var ext:Extender = new Extender();
			//向上转换
			trace (ext as Base); //输出:[object Extender]
			trace (Base(ext));	 //输出:[object Extender]
			
			trace (base as Extender);//输出:null
			trace (Extender(base));  
			//base不是Extender的实例，因此这一句会抛出异常:
			//TypeError: Error #1034: 强制转换类型失败
		}
	}
}
class Base {}
class Extender extends Base {}