public class Timer extends Object implements 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.
For more examples and help in choosing between
this Timer class and
java.util.Timer,
see
Using Timers in Swing Applications,
an article in The Swing Connection.
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 JavaBeansTM
has been added to the java.beans package.
Please see XMLEncoder.
java.util.Timer| Modifier and Type | Field and Description |
|---|---|
protected EventListenerList |
listenerList |
| Constructor and Description |
|---|
Timer(int delay,
ActionListener listener)
Creates a
Timer and initializes both the initial delay and
between-event delay to delay milliseconds. |
| Modifier and Type | Method and Description |
|---|---|
void |
addActionListener(ActionListener listener)
Adds an action listener to the
Timer. |
protected void |
fireActionPerformed(ActionEvent e)
Notifies all listeners that have registered interest for
notification on this event type.
|
String |
getActionCommand()
Returns the string that will be delivered as the action command
in
ActionEvents fired by this timer. |
ActionListener[] |
getActionListeners()
Returns an array of all the action listeners registered
on this timer.
|
int |
getDelay()
Returns the delay, in milliseconds,
between firings of action events.
|
int |
getInitialDelay()
Returns the
Timer's initial delay. |
<T extends EventListener> |
getListeners(Class<T> listenerType)
Returns an array of all the objects currently registered as
FooListeners
upon this Timer. |
static boolean |
getLogTimers()
Returns
true if logging is enabled. |
boolean |
isCoalesce()
Returns
true if the Timer coalesces
multiple pending action events. |
boolean |
isRepeats()
Returns
true (the default)
if the Timer will send
an action event
to its listeners multiple times. |
boolean |
isRunning()
Returns
true if the Timer is running. |
void |
removeActionListener(ActionListener listener)
Removes the specified action listener from the
Timer. |
void |
restart()
Restarts the
Timer,
canceling any pending firings and causing
it to fire with its initial delay. |
void |
setActionCommand(String command)
Sets the string that will be delivered as the action command
in
ActionEvents fired by this timer. |
void |
setCoalesce(boolean flag)
Sets whether the
Timer coalesces multiple pending
ActionEvent firings. |
void |
setDelay(int delay)
Sets the
Timer's between-event delay, the number of milliseconds
between successive action events. |
void |
setInitialDelay(int initialDelay)
Sets the
Timer's initial delay, the time
in milliseconds to wait after the timer is started
before firing the first event. |
static void |
setLogTimers(boolean flag)
Enables or disables the timer log.
|
void |
setRepeats(boolean flag)
If
flag is false,
instructs the Timer to send only one
action event to its listeners. |
void |
start()
Starts the
Timer,
causing it to start sending action events
to its listeners. |
void |
stop()
Stops the
Timer,
causing it to stop sending action events
to its listeners. |
protected EventListenerList listenerList
public Timer(int delay,
ActionListener listener)
Timer and initializes both the initial delay and
between-event delay to delay milliseconds. If delay
is less than or equal to zero, the timer fires as soon as it
is started. If listener is not null,
it's registered as an action listener on the timer.delay - milliseconds for the initial and between-event delaylistener - an initial listener; can be nulladdActionListener(java.awt.event.ActionListener),
setInitialDelay(int),
setRepeats(boolean)public void addActionListener(ActionListener listener)
Timer.listener - the listener to addTimer(int, java.awt.event.ActionListener)public void removeActionListener(ActionListener listener)
Timer.listener - the listener to removepublic ActionListener[] getActionListeners()
ActionListeners or an empty
array if no action listeners are currently registeredaddActionListener(java.awt.event.ActionListener),
removeActionListener(java.awt.event.ActionListener)protected void fireActionPerformed(ActionEvent e)
e - the action event to fireEventListenerListpublic <T extends EventListener> T[] getListeners(Class<T> listenerType)
FooListeners
upon this Timer.
FooListeners
are registered using the addFooListener method.
You can specify the listenerType argument
with a class literal, such as FooListener.class.
For example, you can query a Timer
instance t
for 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.
listenerType - the type of listeners requested;
this parameter should specify an interface
that descends from java.util.EventListenerFooListeners
on this timer,
or an empty array if no such
listeners have been addedClassCastException - if listenerType doesn't
specify a class or interface that implements
java.util.EventListenergetActionListeners(),
addActionListener(java.awt.event.ActionListener),
removeActionListener(java.awt.event.ActionListener)public static void setLogTimers(boolean flag)
System.out whenever the timer goes off.flag - true to enable logginggetLogTimers()public static boolean getLogTimers()
true if logging is enabled.true if logging is enabled; otherwise, falsesetLogTimers(boolean)public void setDelay(int delay)
Timer'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 the setInitialDelay method.delay - the delay in millisecondssetInitialDelay(int)public int getDelay()
setDelay(int),
getInitialDelay()public void setInitialDelay(int initialDelay)
Timer'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.initialDelay - the initial delay, in millisecondssetDelay(int)public int getInitialDelay()
Timer's initial delay.setInitialDelay(int),
setDelay(int)public void setRepeats(boolean flag)
flag is false,
instructs the Timer to send only one
action event to its listeners.flag - specify false to make the timer
stop after sending its first action eventpublic boolean isRepeats()
true (the default)
if the Timer will send
an action event
to its listeners multiple times.setRepeats(boolean)public void setCoalesce(boolean flag)
Timer coalesces multiple pending
ActionEvent firings.
A busy application may not be able
to keep up with a Timer's event generation,
causing multiple
action events to be queued. When processed,
the application sends these events one after the other, causing the
Timer'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.flag - specify false to turn off coalescingpublic boolean isCoalesce()
true if the Timer coalesces
multiple pending action events.setCoalesce(boolean)public void setActionCommand(String command)
ActionEvents fired by this timer.
null is an acceptable value.command - the action commandpublic String getActionCommand()
ActionEvents fired by this timer. May be
null, which is also the default.public void start()
Timer,
causing it to start sending action events
to its listeners.stop()public boolean isRunning()
true if the Timer is running.start()public void stop()
Timer,
causing it to stop sending action events
to its listeners.start()public void restart()
Timer,
canceling any pending firings and causing
it to fire with its initial delay.