In this chapter you have learned how to handle events in your applications and in your applets. Events are fundamental to all window-based applications, as well as most applets, so you will be applying the techniques from this chapter throughout the rest of the book.
The most important points we have discussed in this chapter are:
A user interaction generates an event in the context of a component.
There are two categories of events associated with a component: low-level events from the mouse, keyboard or window system events such as opening or closing a window, and semantic events which represent component actions such as pressing a button or selecting a menu item.
Both low-level and semantic events can arise simultaneously.
An event for a component can be handled by the component object itself, or by a separate object that implements a listener interface corresponding to the event type.
A component that is to handle its own events does so by calling its enableEvents() method and implementing the class method to process the kind of event that has been enabled.
A listener object that is registered with a component will receive notification of the events originating with the component that correspond to the type(s) of events the listener can handle.
A listener interface for low-level events requires several event-handling methods to be implemented.
A listener interface for semantic events declares a single event handling method.
An adapter class defines a set of empty methods for one or more low-level event interfaces. You can create your own class defining a low-level event listener by deriving your class from an adapter class, and then implementing the event handling methods in which you are interested.
Events in applications and in applets are handled in exactly the same way.
An Action object is an object of a class that implements the Action interface. Action objects can be used to create menu items and associated toolbar buttons.
An Action object is automatically the listener for the menu item and toolbar button that are created from it.