从基础开始深入学Flash AS3教程(3)(译文)
var obj:Object = getMyCustomObject();
vay customObj:MyClass = MyClass(obj);
AS3引入了一种新的操作符“as”来进行类型转换。as操作符代替了类型名称语法来改变对象的数据类型。如：
var obj:Object = getMyCustomObject();
vay customObj:MyClass = obj as MyClass;
（本文非直接翻译，原文如下：）
In ActionScript 2, variables defined within a class's body were defined in the class's prototype object. This was an efficient means to handle variable definitions but it also meant that complex data types (such as Arrays) had a tendency to be "shared" among instances if not explicitly defined for instances within the class constructor. This is no longer a problem with ActionScript 3. Class variables defined in the class body are now unique to each class instance so this problem no longer occurs.
在AS2中，复杂数据类型（比如数组），如果在类体之中，方法之外直接初始化，而不在构造器中初始化，会被理解为“共享”的数据，而被所有的实例共享使用（类似于static的效果）。但是在AS3中不存在这个问题。类变量是每个实例独有的，唯一的变量。如下:
class myClass{
private var list:Array = [1,2,3]; //在AS2中会有一定问题，AS3中就很好
public function myClass(){
//在AS2中，应该在这里初始化list
}
}
stage.addEventListener(MouseEvent.MOUSE_MOVE, dragMyObject);