Class Timer
- java.lang.Object
-
- javax.swing.Timer
- All Implemented Interfaces:
Serializable
public class Timer extends Object implements Serializable
Fires one or more ActionEvent
s 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 Timer
s perform their waiting using a single, shared thread (created by the first Timer
object that executes), the action event handlers for Timer
s execute on another thread -- the event-dispatching thread. This means that the action handlers for Timer
s 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 JavaBeans™ has been added to the java.beans
package. Please see XMLEncoder
.
- Since:
- 1.2
- See Also:
-
Timer
, Serialized Form
Field Summary
Modifier and Type | Field | Description |
---|---|---|
protected EventListenerList | listenerList | The collection of registered listeners |
Constructor Summary
Constructor | Description |
---|---|
Timer(int delay,
ActionListener listener) | Creates a |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
void | addActionListener(ActionListener listener) | Adds an action listener to the |
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 |
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 |
<T extends EventListener> | getListeners(Class<T> listenerType) | Returns an array of all the objects currently registered as |
static boolean | getLogTimers() | Returns |
boolean | isCoalesce() | Returns |
boolean | isRepeats() | Returns |
boolean | isRunning() | Returns |
void | removeActionListener(ActionListener listener) | Removes the specified action listener from the |
void | restart() | Restarts the |
void | setActionCommand(String command) | Sets the string that will be delivered as the action command in |
void | setCoalesce(boolean flag) | Sets whether the |
void | setDelay(int delay) | Sets the |
void | setInitialDelay(int initialDelay) | Sets the |
static void | setLogTimers(boolean flag) | Enables or disables the timer log. |
void | setRepeats(boolean flag) | If |
void | start() | Starts the |
void | stop() | Stops the |
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Field Detail
listenerList
protected EventListenerList listenerList
The collection of registered listeners
Constructor Detail
Timer
public Timer(int delay, ActionListener listener)
Creates a 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.
- Parameters:
-
delay
- milliseconds for the initial and between-event delay -
listener
- an initial listener; can benull
- See Also:
-
addActionListener(java.awt.event.ActionListener)
,setInitialDelay(int)
,setRepeats(boolean)
Method Detail
addActionListener
public void addActionListener(ActionListener listener)
Adds an action listener to the Timer
.
- Parameters:
-
listener
- the listener to add - See Also:
Timer(int, java.awt.event.ActionListener)
removeActionListener
public void removeActionListener(ActionListener listener)
Removes the specified action listener from the Timer
.
- Parameters:
-
listener
- the listener to remove
getActionListeners
public ActionListener[] getActionListeners()
Returns an array of all the action listeners registered on this timer.
- Returns:
- all of the timer's
ActionListener
s or an empty array if no action listeners are currently registered - Since:
- 1.4
- See Also:
-
addActionListener(java.awt.event.ActionListener)
,removeActionListener(java.awt.event.ActionListener)
fireActionPerformed
protected void fireActionPerformed(ActionEvent e)
Notifies all listeners that have registered interest for notification on this event type.
- Parameters:
-
e
- the action event to fire - See Also:
EventListenerList
getListeners
public <T extends EventListener> T[] getListeners(Class<T> listenerType)
Returns an array of all the objects currently registered as FooListener
s upon this Timer
. FooListener
s 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.
- Type Parameters:
-
T
- the type ofEventListener
class 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
FooListener
s on this timer, or an empty array if no such listeners have been added - Throws:
-
ClassCastException
- iflistenerType
doesn't specify a class or interface that implementsjava.util.EventListener
- Since:
- 1.3
- See Also:
-
getActionListeners()
,addActionListener(java.awt.event.ActionListener)
,removeActionListener(java.awt.event.ActionListener)
setLogTimers
public static void setLogTimers(boolean flag)
Enables or disables the timer log. When enabled, a message is posted to System.out
whenever the timer goes off.
- Parameters:
-
flag
-true
to enable logging - See Also:
getLogTimers()
getLogTimers
public static boolean getLogTimers()
Returns true
if logging is enabled.
- Returns:
-
true
if logging is enabled; otherwise, false - See Also:
setLogTimers(boolean)
setDelay
public void setDelay(int delay)
Sets the 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.
- Parameters:
-
delay
- the delay in milliseconds - See Also:
setInitialDelay(int)
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:
-
setDelay(int)
,getInitialDelay()
setInitialDelay
public 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. 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:
setDelay(int)
getInitialDelay
public int getInitialDelay()
Returns the Timer
's initial delay.
- Returns:
- the
Timer
's intial delay, in milliseconds - See Also:
-
setInitialDelay(int)
,setDelay(int)
setRepeats
public void setRepeats(boolean flag)
If flag
is false
, instructs the Timer
to send only one action event to its listeners.
- Parameters:
-
flag
- specifyfalse
to make the timer stop after sending its first action event
isRepeats
public boolean isRepeats()
Returns true
(the default) if the Timer
will send an action event to its listeners multiple times.
- Returns:
- true if the
Timer
will send an action event to its listeners multiple times - See Also:
setRepeats(boolean)
setCoalesce
public void setCoalesce(boolean flag)
Sets whether the 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. Timer
s coalesce events by default.
- Parameters:
-
flag
- specifyfalse
to turn off coalescing
isCoalesce
public boolean isCoalesce()
Returns true
if the Timer
coalesces multiple pending action events.
- Returns:
- true if the
Timer
coalesces multiple pending action events - See Also:
setCoalesce(boolean)
setActionCommand
public void setActionCommand(String command)
Sets the string that will be delivered as the action command in ActionEvent
s fired by this timer. null
is an acceptable value.
- Parameters:
-
command
- the action command - Since:
- 1.6
getActionCommand
public String getActionCommand()
Returns the string that will be delivered as the action command in ActionEvent
s fired by this timer. May be null
, which is also the default.
- Returns:
- the action command used in firing events
- Since:
- 1.6
start
public void start()
Starts the Timer
, causing it to start sending action events to its listeners.
- See Also:
stop()
isRunning
public boolean isRunning()
Returns true
if the Timer
is running.
- Returns:
- true if the
Timer
is running, false otherwise - See Also:
start()
stop
public void stop()
Stops the Timer
, causing it to stop sending action events to its listeners.
- See Also:
start()
restart
public void restart()
Restarts the Timer
, canceling any pending firings and causing it to fire with its initial delay.