Timer (Java Platform SE 8 )
Keywords: javax.swing.Timer class
Date: 2020-03-26

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 `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`.

  See Also:
    ``java.util.Timer``

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected EventListenerList` | `listenerList`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `Timer(int delay, ActionListener listener)` Creates a `Timer` and initializes both the initial delay and between-event delay to `delay` milliseconds.

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    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 `ActionEvent`s 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> T[]` | `getListeners(Class<T> listenerType)` Returns an array of all the objects currently registered as `FooListener`s 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 `ActionEvent`s 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.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### listenerList

          protected EventListenerList listenerList

  - ### 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 be `null`
      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.
      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 `FooListener`s 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 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.
      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.
      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. `Timer`s 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)`

    - #### 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.
      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.

Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
Copyright © 1993, 2020, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.