Java Reference
In-Depth Information
Display 17.1
Event Firing and an Event Listener
The component (for
example, a button) fires an
event.
event
component
listener
This listener object invokes an event handler
method with the
event
as an argument.
the next thing that happens depends on the next event. It's as though the listeners were
robots that interact with other objects (possibly other robots) in response to events
(signals) from these other objects. You program the robots, but the environment and
other robots determine what any particular robot will actually end up doing.
If you have never done event-driven programming before, one aspect of it may
seem strange to you:
You will be writing definitions for methods that you will never invoke
in any program.
This will likely feel a bit strange at first, because a method is of no
value unless it is invoked. So, somebody or something other than you, the program-
mer, must be invoking these methods. That is exactly what does happen. The Swing
system automatically invokes certain methods when an event signals that the method
needs to be called.
Event-driven programming with the Swing library makes extensive use of inheri-
tance. The classes you define will be derived classes of some basic Swing library classes.
These derived classes will inherit methods from their base class. For many of these
inherited methods, library software will determine when these methods are invoked,
but you will override the definition of the inherited method to determine what will
happen when the method is invoked.
17.2
Buttons, Events, and Other Swing Basics
One button click is worth a thousand key strokes.
ANONYMOUS
In this section we present enough about Swing to allow you to do some simple GUI
programs.
