https://openjdk.java.net/ 
/*
 * Copyright (c) 1997, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */



package javax.swing;



import java.util.*;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.locks.*;
import java.awt.*;
import java.awt.event.*;
import java.io.Serializable;
import java.io.*;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import javax.swing.event.EventListenerList;




Fires one or more 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. 
Author:Dave Moore
See Also:
/**
 * Fires one or more {@code ActionEvent}s at specified
 * intervals. An example use is an animation object that uses a
 * <code>Timer</code> as the trigger for drawing its frames.
 *<p>
 * Setting up a timer
 * involves creating a <code>Timer</code> object,
 * registering one or more action listeners on it,
 * and starting the timer using
 * the <code>start</code> 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 <code>Timer</code> constructor).
 * The second argument to the <code>Timer</code> constructor
 * specifies a listener to receive the timer's action events.
 *
 *<pre>
 *  int delay = 1000; //milliseconds
 *  ActionListener taskPerformer = new ActionListener() {
 *      public void actionPerformed(ActionEvent evt) {
 *          <em>//...Perform a task...</em>
 *      }
 *  };
 *  new Timer(delay, taskPerformer).start();</pre>
 *
 * <p>
 * {@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 <code>ActionEvent</code> to registered listeners.
 * After this first event, it continues to fire events
 * every time the between-event delay has elapsed, until it
 * is stopped.
 * <p>
 * After construction, the initial delay and the between-event
 * delay can be changed independently, and additional
 * <code>ActionListeners</code> may be added.
 * <p>
 * If you want the timer to fire only the first time and then stop,
 * invoke <code>setRepeats(false)</code> on the timer.
 * <p>
 * Although all <code>Timer</code>s perform their waiting
 * using a single, shared thread
 * (created by the first <code>Timer</code> object that executes),
 * the action event handlers for <code>Timer</code>s
 * execute on another thread -- the event-dispatching thread.
 * This means that the action handlers for <code>Timer</code>s
 * can safely perform operations on Swing components.
 * However, it also means that the handlers must execute quickly
 * to keep the GUI responsive.
 *
 * <p>
 * In v 1.3, another <code>Timer</code> class was added
 * to the Java platform: <code>java.util.Timer</code>.
 * Both it and <code>javax.swing.Timer</code>
 * provide the same basic functionality,
 * but <code>java.util.Timer</code>
 * is more general and has more features.
 * The <code>javax.swing.Timer</code> 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.
 *
 * <p>
 * You can find further documentation
 * and several examples of using timers by visiting
 * <a href="http://java.sun.com/docs/books/tutorial/uiswing/misc/timer.html"
 * target = "_top">How to Use Timers</a>,
 * a section in <em>The Java Tutorial.</em>
 * For more examples and help in choosing between
 * this <code>Timer</code> class and
 * <code>java.util.Timer</code>,
 * see
 * <a href="http://java.sun.com/products/jfc/tsc/articles/timer/"
 * target="_top">Using Timers in Swing Applications</a>,
 * an article in <em>The Swing Connection.</em>
 * <p>
 * <strong>Warning:</strong>
 * 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<sup><font size="-2">TM</font></sup>
 * has been added to the <code>java.beans</code> package.
 * Please see {@link java.beans.XMLEncoder}.
 *
 * @see java.util.Timer <code>java.util.Timer</code>
 *
 *
 * @author Dave Moore
 */
public class Timer implements Serializable
{
    /*
     * NOTE: all fields need to be handled in readResolve
     */

    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 transient final AtomicBoolean notify = new AtomicBoolean(false);

    private volatile int     initialDelay, delay;
    private volatile boolean repeats = true, coalesce = true;

    private transient final Runnable doPostEvent;

    private static volatile boolean logTimers;

    private transient final Lock lock = new ReentrantLock();

    /*
     * The timer's AccessControlContext.
     */
     private transient volatile AccessControlContext acc =
            AccessController.getContext();

    
Returns the acc this timer was constructed with.

/**
      * Returns the acc this timer was constructed with.
      */
     final AccessControlContext getAccessControlContext() {
       if (acc == null) {
           throw new SecurityException(
                   "Timer is missing AccessControlContext");
       }
       return acc;
     }

    // 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 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.

Params:
  • delay – milliseconds for the initial and between-event delay
  • listener –  an initial listener; can be null
See Also:
/**
     * 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 <code>listener</code> is not <code>null</code>,
     * 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 <code>null</code>

     * @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);
        }
    }

    
DoPostEvent is a runnable class that fires actionEvents to
the listeners on the EventDispatchThread, via invokeLater.

See Also:
  • post.post
/**
     * 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.

Params:
  • listener – the listener to add
See Also:
/**
     * Adds an action listener to the <code>Timer</code>.
     *
     * @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.

Params:
  • listener – the listener to remove
/**
     * Removes the specified action listener from the <code>Timer</code>.
     *
     * @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.

See Also:
Returns:all of the timer's ActionListeners or an empty
        array if no action listeners are currently registered
Since:1.4
/**
     * Returns an array of all the action listeners registered
     * on this timer.
     *
     * @return all of the timer's <code>ActionListener</code>s 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.

Params:
  • e – the action event to fire
See Also:
/**
     * 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.

Params:
  • listenerType –  the type of listeners requested;
         this parameter should specify an interface
         that descends from java.util.EventListener
Throws:
  • ClassCastException – if listenerType doesn't
         specify a class or interface that implements
         java.util.EventListener
See Also:
Returns:an array of all objects registered as
         FooListeners
         on this timer,
         or an empty array if no such
         listeners have been added
Since:1.3
/**
     * Returns an array of all the objects currently registered as
     * <code><em>Foo</em>Listener</code>s
     * upon this <code>Timer</code>.
     * <code><em>Foo</em>Listener</code>s
     * are registered using the <code>add<em>Foo</em>Listener</code> method.
     * <p>
     * You can specify the <code>listenerType</code> argument
     * with a class literal, such as <code><em>Foo</em>Listener.class</code>.
     * For example, you can query a <code>Timer</code>
     * instance <code>t</code>
     * for its action listeners
     * with the following code:
     *
     * <pre>ActionListener[] als = (ActionListener[])(t.getListeners(ActionListener.class));</pre>
     *
     * If no such listeners exist,
     * this method returns an empty array.
     *
     * @param listenerType  the type of listeners requested;
     *          this parameter should specify an interface
     *          that descends from <code>java.util.EventListener</code>
     * @return an array of all objects registered as
     *          <code><em>Foo</em>Listener</code>s
     *          on this timer,
     *          or an empty array if no such
     *          listeners have been added
     * @exception ClassCastException if <code>listenerType</code> doesn't
     *          specify a class or interface that implements
     *          <code>java.util.EventListener</code>
     *
     * @see #getActionListeners
     * @see #addActionListener
     * @see #removeActionListener
     *
     * @since 1.3
     */
    public <T extends EventListener> T[] getListeners(Class<T> listenerType) {
        return listenerList.getListeners(listenerType);
    }

    
Returns the timer queue.

/**
     * Returns the timer queue.
     */
    private TimerQueue timerQueue() {
        return TimerQueue.sharedInstance();
    }


    
Enables or disables the timer log. When enabled, a message
is posted to System.out whenever the timer goes off.

Params:
  • flag –  true to enable logging
See Also:
/**
     * Enables or disables the timer log. When enabled, a message
     * is posted to <code>System.out</code> whenever the timer goes off.
     *
     * @param flag  <code>true</code> to enable logging
     * @see #getLogTimers
     */
    public static void setLogTimers(boolean flag) {
        logTimers = flag;
    }


    
Returns true if logging is enabled.

See Also:
Returns:true if logging is enabled; otherwise, false
/**
     * Returns <code>true</code> if logging is enabled.
     *
     * @return <code>true</code> 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 setInitialDelay method. 
Params:
  • delay – the delay in milliseconds
See Also:
/**
     * Sets the <code>Timer</code>'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) {
        if (delay < 0) {
            throw new IllegalArgumentException("Invalid delay: " + delay);
        }
        else {
            this.delay = delay;
        }
    }


    
Returns the delay, in milliseconds,
between firings of action events.

See Also:
/**
     * Returns 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.

Params:
  • initialDelay – the initial delay, in milliseconds
See Also:
/**
     * Sets the <code>Timer</code>'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) {
        if (initialDelay < 0) {
            throw new IllegalArgumentException("Invalid initial delay: " +
                                               initialDelay);
        }
        else {
            this.initialDelay = initialDelay;
        }
    }


    
Returns the Timer's initial delay.

See Also:
/**
     * Returns the <code>Timer</code>'s initial delay.
     *
     * @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.

Params:
  • flag – specify false to make the timer
            stop after sending its first action event
/**
     * If <code>flag</code> is <code>false</code>,
     * instructs the <code>Timer</code> to send only one
     * action event to its listeners.
     *
     * @param flag specify <code>false</code> 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.

See Also:
  • setRepeats
/**
     * Returns <code>true</code> (the default)
     * if the <code>Timer</code> 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.

Params:
  • flag – specify false to turn off coalescing
/**
     * Sets whether the <code>Timer</code> coalesces multiple pending
     * <code>ActionEvent</code> firings.
     * A busy application may not be able
     * to keep up with a <code>Timer</code>'s event generation,
     * causing multiple
     * action events to be queued.  When processed,
     * the application sends these events one after the other, causing the
     * <code>Timer</code>'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.
     * <code>Timer</code>s
     * coalesce events by default.
     *
     * @param flag specify <code>false</code> 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 true if the Timer coalesces
multiple pending action events.

See Also:
  • setCoalesce
/**
     * Returns <code>true</code> if the <code>Timer</code> 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.

Params:
  • command – the action command
Since:1.6
/**
     * Sets the string that will be delivered as the action command
     * in <code>ActionEvent</code>s fired by this timer.
     * <code>null</code> 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.

Returns:the action command used in firing events
Since:1.6
/**
     * Returns the string that will be delivered as the action command
     * in <code>ActionEvent</code>s fired by this timer. May be
     * <code>null</code>, 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 Also:
  • stop
/**
     * Starts the <code>Timer</code>,
     * causing it to start sending action events
     * to its listeners.
     *
     * @see #stop
     */
     public void start() {
        timerQueue().addTimer(this, getInitialDelay());
    }


    
Returns true if the Timer is running.

See Also:
  • start
/**
     * Returns <code>true</code> if the <code>Timer</code> is running.
     *
     * @see #start
     */
    public boolean isRunning() {
        return timerQueue().containsTimer(this);
    }


    
Stops the Timer,
causing it to stop sending action events
to its listeners.

See Also:
  • start
/**
     * Stops the <code>Timer</code>,
     * 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.

/**
     * Restarts the <code>Timer</code>,
     * 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.

/**
     * 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 <code>stop</code> for that.
     */
    void cancelEvent() {
        notify.set(false);
    }


    void post() {
        if (notify.compareAndSet(false, true) || !coalesce) {
            AccessController.doPrivileged(new PrivilegedAction<Void>() {
                public Void run() {
                    SwingUtilities.invokeLater(doPostEvent);
                    return null;
                 }
            }, getAccessControlContext());
        }
    }

    Lock getLock() {
        return lock;
    }

    /*
     * We have to use readResolve because we can not initialize final
     * fields for deserialized object otherwise
     */
    private Object readResolve() {
        Timer timer = new Timer(getDelay(), null);
        timer.listenerList = listenerList;
        timer.initialDelay = initialDelay;
        timer.delay = delay;
        timer.repeats = repeats;
        timer.coalesce = coalesce;
        timer.actionCommand = actionCommand;
        return timer;
    }

     private void readObject(ObjectInputStream in) 
        throws ClassNotFoundException, IOException
     {
        this.acc = AccessController.getContext();
        in.defaultReadObject();
     }
}