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();
*
*
* {@code Timers} are constructed by specifying both a delay parameter
* and an {@code 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 {@link java.beans.XMLEncoder}.
*
* @see java.util.Timer
*
*
* @author Dave Moore
* @since 1.2
*/
@SuppressWarnings("serial")
public class Timer implements Serializable
{
/*
* NOTE: all fields need to be handled in readResolve
*/
/**
* The collection of registered listeners
*/
protected EventListenerList listenerList = new EventListenerList();
// The following field strives to maintain the following:
// If coalesce is true, only allow one Runnable to be queued on the
// EventQueue and be pending (ie in the process of notifying the
// ActionListener). If we didn't do this it would allow for a
// situation where the app is taking too long to process the
// actionPerformed, and thus we'ld end up queing a bunch of Runnables
// and the app would never return: not good. This of course implies
// you can get dropped events, but such is life.
// notify is used to indicate if the ActionListener can be notified, when
// the Runnable is processed if this is true it will notify the listeners.
// notify is set to true when the Timer fires and the Runnable is queued.
// It will be set to false after notifying the listeners (if coalesce is
// true) or if the developer invokes stop.
private final transient AtomicBoolean notify = new AtomicBoolean(false);
private volatile int initialDelay, delay;
private volatile boolean repeats = true, coalesce = true;
private final transient Runnable doPostEvent;
private static volatile boolean logTimers;
private final transient Lock lock = new ReentrantLock();
// This field is maintained by TimerQueue.
// eventQueued can also be reset by the TimerQueue, but will only ever
// happen in applet case when TimerQueues thread is destroyed.
// access to this field is synchronized on getLock() lock.
transient TimerQueue.DelayedTimer delayedTimer = null;
private volatile String actionCommand;
/**
* Creates a {@code Timer} and initializes both the initial delay and
* between-event delay to {@code delay} milliseconds. If {@code 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.
*
* @param delay milliseconds for the initial and between-event delay
* @param listener an initial listener; can be null
*
* @see #addActionListener
* @see #setInitialDelay
* @see #setRepeats
*/
public Timer(int delay, ActionListener listener) {
super();
this.delay = delay;
this.initialDelay = delay;
doPostEvent = new DoPostEvent();
if (listener != null) {
addActionListener(listener);
}
}
/*
* The timer's AccessControlContext.
*/
private transient volatile AccessControlContext acc =
AccessController.getContext();
/**
* Returns the acc this timer was constructed with.
*/
final AccessControlContext getAccessControlContext() {
if (acc == null) {
throw new SecurityException(
"Timer is missing AccessControlContext");
}
return acc;
}
/**
* DoPostEvent is a runnable class that fires actionEvents to
* the listeners on the EventDispatchThread, via invokeLater.
* @see Timer#post
*/
class DoPostEvent implements Runnable
{
public void run() {
if (logTimers) {
System.out.println("Timer ringing: " + Timer.this);
}
if(notify.get()) {
fireActionPerformed(new ActionEvent(Timer.this, 0, getActionCommand(),
System.currentTimeMillis(),
0));
if (coalesce) {
cancelEvent();
}
}
}
Timer getTimer() {
return Timer.this;
}
}
/**
* Adds an action listener to the Timer.
*
* @param listener the listener to add
*
* @see #Timer
*/
public void addActionListener(ActionListener listener) {
listenerList.add(ActionListener.class, listener);
}
/**
* Removes the specified action listener from the Timer.
*
* @param listener the listener to remove
*/
public void removeActionListener(ActionListener listener) {
listenerList.remove(ActionListener.class, listener);
}
/**
* Returns an array of all the action listeners registered
* on this timer.
*
* @return all of the timer's ActionListeners or an empty
* array if no action listeners are currently registered
*
* @see #addActionListener
* @see #removeActionListener
*
* @since 1.4
*/
public ActionListener[] getActionListeners() {
return listenerList.getListeners(ActionListener.class);
}
/**
* Notifies all listeners that have registered interest for
* notification on this event type.
*
* @param e the action event to fire
* @see EventListenerList
*/
protected void fireActionPerformed(ActionEvent e) {
// Guaranteed to return a non-null array
Object[] listeners = listenerList.getListenerList();
// Process the listeners last to first, notifying
// those that are interested in this event
for (int i=listeners.length-2; i>=0; i-=2) {
if (listeners[i]==ActionListener.class) {
((ActionListener)listeners[i+1]).actionPerformed(e);
}
}
}
/**
* Returns an array of all the objects currently registered as
* 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. * * @param
java.util.EventListener
* @return an array of all objects registered as
* FooListeners
* on this timer,
* or an empty array if no such
* listeners have been added
* @exception ClassCastException if listenerType doesn't
* specify a class or interface that implements
* java.util.EventListener
*
* @see #getActionListeners
* @see #addActionListener
* @see #removeActionListener
*
* @since 1.3
*/
public System.out whenever the timer goes off.
*
* @param flag true to enable logging
* @see #getLogTimers
*/
public static void setLogTimers(boolean flag) {
logTimers = flag;
}
/**
* Returns true if logging is enabled.
*
* @return true if logging is enabled; otherwise, false
* @see #setLogTimers
*/
public static boolean getLogTimers() {
return logTimers;
}
/**
* 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 {@code setInitialDelay} method.
*
* @param delay the delay in milliseconds
* @see #setInitialDelay
*/
public void setDelay(int delay) {
checkDelay(delay, "Invalid delay: ");
this.delay = delay;
}
private static void checkDelay(int delay, String message) {
if (delay < 0) {
throw new IllegalArgumentException(message + delay);
}
}
/**
* Returns the delay, in milliseconds,
* between firings of action events.
*
* @return the delay, in milliseconds, between firings of action events
* @see #setDelay
* @see #getInitialDelay
*/
public int getDelay() {
return delay;
}
/**
* 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.
*
* @param initialDelay the initial delay, in milliseconds
* @see #setDelay
*/
public void setInitialDelay(int initialDelay) {
checkDelay(initialDelay, "Invalid initial delay: ");
this.initialDelay = initialDelay;
}
/**
* Returns the {@code Timer}'s initial delay.
*
* @return the {@code Timer}'s intial delay, in milliseconds
* @see #setInitialDelay
* @see #setDelay
*/
public int getInitialDelay() {
return initialDelay;
}
/**
* If flag is false,
* instructs the Timer to send only one
* action event to its listeners.
*
* @param flag specify false to make the timer
* stop after sending its first action event
*/
public void setRepeats(boolean flag) {
repeats = flag;
}
/**
* Returns true (the default)
* if the Timer will send
* an action event
* to its listeners multiple times.
*
* @return true if the {@code Timer} will send an action event to its
* listeners multiple times
* @see #setRepeats
*/
public boolean isRepeats() {
return repeats;
}
/**
* 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.
* Timers
* coalesce events by default.
*
* @param flag specify false to turn off coalescing
*/
public void setCoalesce(boolean flag) {
boolean old = coalesce;
coalesce = flag;
if (!old && coalesce) {
// We must do this as otherwise if the Timer once notified
// in !coalese mode notify will be stuck to true and never
// become false.
cancelEvent();
}
}
/**
* Returns {@code true} if the {@code Timer} coalesces
* multiple pending action events.
*
* @return true if the {@code Timer} coalesces multiple pending
* action events
* @see #setCoalesce
*/
public boolean isCoalesce() {
return coalesce;
}
/**
* Sets the string that will be delivered as the action command
* in ActionEvents fired by this timer.
* null is an acceptable value.
*
* @param command the action command
* @since 1.6
*/
public void setActionCommand(String command) {
this.actionCommand = command;
}
/**
* Returns the string that will be delivered as the action command
* in ActionEvents fired by this timer. May be
* null, which is also the default.
*
* @return the action command used in firing events
* @since 1.6
*/
public String getActionCommand() {
return actionCommand;
}
/**
* Starts the Timer,
* causing it to start sending action events
* to its listeners.
*
* @see #stop
*/
public void start() {
timerQueue().addTimer(this, getInitialDelay());
}
/**
* Returns {@code true} if the {@code Timer} is running.
*
* @return true if the {@code Timer} is running, false otherwise
* @see #start
*/
public boolean isRunning() {
return timerQueue().containsTimer(this);
}
/**
* Stops the Timer,
* causing it to stop sending action events
* to its listeners.
*
* @see #start
*/
public void stop() {
getLock().lock();
try {
cancelEvent();
timerQueue().removeTimer(this);
} finally {
getLock().unlock();
}
}
/**
* Restarts the Timer,
* canceling any pending firings and causing
* it to fire with its initial delay.
*/
public void restart() {
getLock().lock();
try {
stop();
start();
} finally {
getLock().unlock();
}
}
/**
* Resets the internal state to indicate this Timer shouldn't notify
* any of its listeners. This does not stop a repeatable Timer from
* firing again, use stop for that.
*/
void cancelEvent() {
notify.set(false);
}
void post() {
if (notify.compareAndSet(false, true) || !coalesce) {
AccessController.doPrivileged(new PrivilegedAction