flex的条件判断：存在即为true

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" creationComplete="init()">
	<mx:Script>
		<![CDATA[
			import mx.controls.Alert;
			private var str:String = null;
			private var o:Object = "123";
			private function init():void {
				//因为str是空所以条件不成立
				if(str) {
					Alert.show(str.toString());
				}
				//因为o不为空所以条件成立
				if(o) {
					Alert.show(o.toString());
				}
			}
		]]>
	</mx:Script>
</mx:Application>