The listener interface for receiving container events. The class that is interested in processing a container event either implements this interface (and all the methods it contains) or extends the abstract
class (overriding only the methods of interest). The listener object created from that class is then registered with a component using the component's
method. When the container's contents change because a component has been added or removed, the relevant method in the listener object is invoked, and the
is passed to it.
Container events are provided for notification purposes ONLY; The AWT will automatically handle add and remove operations internally so the program works properly regardless of whether the program registers a
ContainerListener or not.