ContainerEventDemo 

ContainerEventDemo is a Java event listener designed to be a Container Listener. This listener is triggered by a Container when a component is added to or removed from it. These events are only for notification, and no listener is required for components to be added or removed. By clicking "Add a button" or "Remove a button", users can add or remove buttons from a panel at the bottom of the window. Each time a button is added or removed, the panel fires a container event and notifies the panel's container listener.