javax.swing
Class Timer

java.lang.Object
  javax.swing.Timer

All Implemented Interfaces:

Serializable

public class Timer

extends Object

implements Serializable

Fires one or more action events after a specified delay. For example, an animation object can use 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();

Each Timer has one or more action listeners and a delay (the time between action events). When delay milliseconds have passed, the Timer fires an action event to its listeners. By default, this cycle repeats until the stop method is called. If you want the timer to fire only once, invoke setRepeats(false) on the timer. To make the delay before the first action event different from the delay between events, use the setInitialDelay method.

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 JavaBeans^TM has been added to the java.beans package. Please see XMLEncoder.

See Also:

java.util.Timer

listenerList

protected EventListenerList listenerList

Timer

public Timer(int delay,
             ActionListener listener)

Creates a Timer that will notify its listeners every delay milliseconds. If delay is less than or equal to zero the timer will fire as soon as it is started. If listener is not null, it's registered as an action listener on the timer.

Parameters:

delay - the number of milliseconds between action events

listener - an initial listener; can be null

See Also:

addActionListener(java.awt.event.ActionListener), setInitialDelay(int), setRepeats(boolean)

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 ActionListeners 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 EventListener[] getListeners(Class listenerType)

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.

Parameters:

listenerType - the type of listeners requested; this parameter should specify an interface that descends from java.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 - if listenerType doesn't specify a class or interface that implements java.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 delay, the number of milliseconds between successive action events.

Parameters:

delay - the delay in milliseconds

See Also:

setInitialDelay(int)

getDelay

public int getDelay()

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, which by default is the same as the between-event delay. This is used only for the first action event. Subsequent action events are spaced using the delay property.

Parameters:

initialDelay - the delay, in milliseconds, between the invocation of the start method and the first action event fired by this timer

See Also:

setDelay(int)

getInitialDelay

public int getInitialDelay()

Returns the Timer's initial delay.

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 - specify false 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.

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. Timers coalesce events by default.

Parameters:

flag - specify false to turn off coalescing

isCoalesce

public boolean isCoalesce()

Returns true if the Timer coalesces multiple pending action events.

See Also:

setCoalesce(boolean)

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.

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.