Class Timer
- All Implemented Interfaces:
Serializable
ActionEvents at specified
intervals. An example use is an animation object that uses a
Timer as the trigger for drawing its frames.
Setting up a timer
involves creating a Timer object,
registering one or more action listeners on it,
and starting the timer using
the start method.
For example,
the following code creates and starts a timer
that fires an action event once per second
(as specified by the first argument to the Timer constructor).
The second argument to the Timer constructor
specifies a listener to receive the timer's action events.
int delay = 1000; //milliseconds
ActionListener taskPerformer = new ActionListener() {
public void actionPerformed(ActionEvent evt) {
//...Perform a task...
}
};
new Timer(delay, taskPerformer).start();
Timers are constructed by specifying both a delay parameter
and an ActionListener. The delay parameter is used
to set both the initial delay and the delay between event
firing, in milliseconds. Once the timer has been started,
it waits for the initial delay before firing its
first ActionEvent to registered listeners.
After this first event, it continues to fire events
every time the between-event delay has elapsed, until it
is stopped.
After construction, the initial delay and the between-event
delay can be changed independently, and additional
ActionListeners may be added.
If you want the timer to fire only the first time and then stop,
invoke setRepeats(false) on the timer.
Although all Timers perform their waiting
using a single, shared thread
(created by the first Timer object that executes),
the action event handlers for Timers
execute on another thread -- the event-dispatching thread.
This means that the action handlers for Timers
can safely perform operations on Swing components.
However, it also means that the handlers must execute quickly
to keep the GUI responsive.
In v 1.3, another Timer class was added
to the Java platform: java.util.Timer.
Both it and javax.swing.Timer
provide the same basic functionality,
but java.util.Timer
is more general and has more features.
The javax.swing.Timer has two features
that can make it a little easier to use with GUIs.
First, its event handling metaphor is familiar to GUI programmers
and can make dealing with the event-dispatching thread
a bit simpler.
Second, its
automatic thread sharing means that you don't have to
take special steps to avoid spawning
too many threads.
Instead, your timer uses the same thread
used to make cursors blink,
tool tips appear,
and so on.
You can find further documentation and several examples of using timers by visiting How to Use Timers, a section in The Java Tutorial.
Warning:
Serialized objects of this class will not be compatible with
future Swing releases. The current serialization support is
appropriate for short term storage or RMI between applications running
the same version of Swing. As of 1.4, support for long term storage
of all JavaBeans
has been added to the java.beans package.
Please see XMLEncoder.
- Since:
- 1.2
- See Also:
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected EventListenerListThe collection of registered listeners -
Constructor Summary
ConstructorsConstructorDescriptionTimer(int delay, ActionListener listener) Creates aTimerand initializes both the initial delay and between-event delay todelaymilliseconds. -
Method Summary
Modifier and TypeMethodDescriptionvoidaddActionListener(ActionListener listener) Adds an action listener to theTimer.protected voidNotifies all listeners that have registered interest for notification on this event type.Returns the string that will be delivered as the action command inActionEvents fired by this timer.Returns an array of all the action listeners registered on this timer.intgetDelay()Returns the delay, in milliseconds, between firings of action events.intReturns theTimer's initial delay.<T extends EventListener>
T[]getListeners(Class<T> listenerType) Returns an array of all the objects currently registered asFooListeners upon thisTimer.static booleanReturnstrueif logging is enabled.booleanReturnstrueif theTimercoalesces multiple pending action events.booleanReturnstrue(the default) if theTimerwill send an action event to its listeners multiple times.booleanReturnstrueif theTimeris running.voidremoveActionListener(ActionListener listener) Removes the specified action listener from theTimer.voidrestart()Restarts theTimer, canceling any pending firings and causing it to fire with its initial delay.voidsetActionCommand(String command) Sets the string that will be delivered as the action command inActionEvents fired by this timer.voidsetCoalesce(boolean flag) Sets whether theTimercoalesces multiple pendingActionEventfirings.voidsetDelay(int delay) Sets theTimer's between-event delay, the number of milliseconds between successive action events.voidsetInitialDelay(int initialDelay) Sets theTimer's initial delay, the time in milliseconds to wait after the timer is started before firing the first event.static voidsetLogTimers(boolean flag) Enables or disables the timer log.voidsetRepeats(boolean flag) Ifflagisfalse, instructs theTimerto send only one action event to its listeners.voidstart()Starts theTimer, causing it to start sending action events to its listeners.voidstop()Stops theTimer, causing it to stop sending action events to its listeners.
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Field Details
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listenerList
The collection of registered listeners
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Constructor Details
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Timer
Creates aTimerand initializes both the initial delay and between-event delay todelaymilliseconds. Ifdelayis less than or equal to zero, the timer fires as soon as it is started. Iflisteneris notnull, it's registered as an action listener on the timer.- Parameters:
delay- milliseconds for the initial and between-event delaylistener- an initial listener; can benull- See Also:
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Method Details
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addActionListener
Adds an action listener to theTimer.- Parameters:
listener- the listener to add- See Also:
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removeActionListener
Removes the specified action listener from theTimer.- Parameters:
listener- the listener to remove
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getActionListeners
Returns an array of all the action listeners registered on this timer.- Returns:
- all of the timer's
ActionListeners or an empty array if no action listeners are currently registered - Since:
- 1.4
- See Also:
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fireActionPerformed
Notifies all listeners that have registered interest for notification on this event type.- Parameters:
e- the action event to fire- See Also:
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getListeners
Returns an array of all the objects currently registered asFooListeners upon thisTimer.FooListeners are registered using theaddFooListenermethod.You can specify the
listenerTypeargument with a class literal, such asFooListener.class. For example, you can query aTimerinstancetfor its action listeners with the following code:ActionListener[] als = (ActionListener[])(t.getListeners(ActionListener.class));
If no such listeners exist, this method returns an empty array.- Type Parameters:
T- the type ofEventListenerclass being requested- Parameters:
listenerType- the type of listeners requested; this parameter should specify an interface that descends fromjava.util.EventListener- Returns:
- an array of all objects registered as
FooListeners on this timer, or an empty array if no such listeners have been added - Throws:
ClassCastException- iflistenerTypedoesn't specify a class or interface that implementsjava.util.EventListener- Since:
- 1.3
- See Also:
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setLogTimers
public static void setLogTimers(boolean flag) Enables or disables the timer log. When enabled, a message is posted toSystem.outwhenever the timer goes off.- Parameters:
flag-trueto enable logging- See Also:
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getLogTimers
public static boolean getLogTimers()Returnstrueif logging is enabled.- Returns:
trueif logging is enabled; otherwise, false- See Also:
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setDelay
public void setDelay(int delay) Sets theTimer's between-event delay, the number of milliseconds between successive action events. This does not affect the initial delay property, which can be set by thesetInitialDelaymethod.- Parameters:
delay- the delay in milliseconds- See Also:
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getDelay
public int getDelay()Returns the delay, in milliseconds, between firings of action events.- Returns:
- the delay, in milliseconds, between firings of action events
- See Also:
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setInitialDelay
public void setInitialDelay(int initialDelay) Sets theTimer's initial delay, the time in milliseconds to wait after the timer is started before firing the first event. Upon construction, this is set to be the same as the between-event delay, but then its value is independent and remains unaffected by changes to the between-event delay.- Parameters:
initialDelay- the initial delay, in milliseconds- See Also:
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getInitialDelay
public int getInitialDelay()Returns theTimer's initial delay.- Returns:
- the
Timer's initial delay, in milliseconds - See Also:
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setRepeats
public void setRepeats(boolean flag) Ifflagisfalse, instructs theTimerto send only one action event to its listeners.- Parameters:
flag- specifyfalseto make the timer stop after sending its first action event
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isRepeats
public boolean isRepeats()Returnstrue(the default) if theTimerwill send an action event to its listeners multiple times.- Returns:
- true if the
Timerwill send an action event to its listeners multiple times - See Also:
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setCoalesce
public void setCoalesce(boolean flag) Sets whether theTimercoalesces multiple pendingActionEventfirings. A busy application may not be able to keep up with aTimer's event generation, causing multiple action events to be queued. When processed, the application sends these events one after the other, causing theTimer's listeners to receive a sequence of events with no delay between them. Coalescing avoids this situation by reducing multiple pending events to a single event.Timers coalesce events by default.- Parameters:
flag- specifyfalseto turn off coalescing
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isCoalesce
public boolean isCoalesce()Returnstrueif theTimercoalesces multiple pending action events.- Returns:
- true if the
Timercoalesces multiple pending action events - See Also:
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setActionCommand
Sets the string that will be delivered as the action command inActionEvents fired by this timer.nullis an acceptable value.- Parameters:
command- the action command- Since:
- 1.6
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getActionCommand
Returns the string that will be delivered as the action command inActionEvents fired by this timer. May benull, which is also the default.- Returns:
- the action command used in firing events
- Since:
- 1.6
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start
public void start()Starts theTimer, causing it to start sending action events to its listeners.- See Also:
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isRunning
public boolean isRunning()Returnstrueif theTimeris running.- Returns:
- true if the
Timeris running, false otherwise - See Also:
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stop
public void stop()Stops theTimer, causing it to stop sending action events to its listeners.- See Also:
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restart
public void restart()Restarts theTimer, canceling any pending firings and causing it to fire with its initial delay.
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