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| | Originally, in JDK 1.0, Java shipped with a simple AWT for portable GUI
programming. It used a model for events based on class inheritance:
- In order for a program to catch
and process GUI events, it must subclass GUI
components and override either action() or
handleEvent() methods.
- Returning true from one of these methods consumes the
event so it is not processed further.
- Otherwise the event is propagated
sequentially up the GUI hierarchy until:
- it is consumed, or
- the root of the hierarchy
is reached.
This means that programs have two choices
for structuring their event handling code:
- Each individual component can be
subclassed to specifically handle its target
events; the result is a plethora of classes.
or:
- All events for an entire hierarchy
(or subset) can be handled by a particular
container; the result is that the container's
overridden action() or
handleEvent() method must contain a complex
conditional statement in order to process the
events.
Note: If you ever find yourself writing action() or
handleEvent() methods in
your Java GUI programs, STOP! You're using the old (prehistoric!) event
model. Instead, learn and use the newer, much superior, event model.
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