Java Reference
In-Depth Information
Table 2-1.
Timer Properties
Property Name
Data Type
Access
actionListeners
ActionListener[ ]
Read-only
coalesce
boolean
Read-write
delay
int
Read-write
initialDelay
int
Read-write
repeats
boolean
Read-write
running
boolean
Read-only
The
delay
property is the same as the constructor argument. If you change the delay of a
running timer, the new delay won't be used until the existing delay runs out.
The
initialDelay
property allows you to have another startup delay besides the periodic
delay after the first execution. For instance, if you don't want to initially do a task for an hour,
but then want to do it every 15 minutes thereafter, you need to change the
initialDelay
setting
before you start the timer. By default, the
initialDelay
and
delay
properties are set to the same
setting in the constructor.
The
repeats
property is
true
by default, which results in a repeating timer. When
false
,
the timer notifies action listeners only once. You then need to
restart()
the timer to trigger the
listener again. Nonrepeating timers are good for onetime notifications that need to happen
after a triggering event.
The
coalesce
property allows for a busy system to throw away notifications that haven't
happened yet when a new event needs to be fired to the registered
ActionListener
objects. By
default, the
coalesce
value is
true
. This means if a timer runs every 500 milliseconds, but its
system is bogged down and doesn't respond for a whole 2 seconds, the timer needs to send
only one message, rather than also sending the missing ones. If the setting were
false
, four
messages would still need to be sent.
In addition to the properties just listed, you can turn on log messages with the following
line of code:
Timer.setLogTimers(true);
Log messages are good for actions that lack a visual element, allowing you to see when
something happens.
Tip
The
java.util.Timer
class works in a fashion similar to the
javax.swing.Timer
class, except that
it doesn't run the scheduled task in the event-dispatch thread. In addition, it supports executing tasks at a
fixed rate, versus after a fixed delay. The latter scheme permits the repeat rate to drift between executions if
the event-dispatch thread is busy.
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