java.awt.EventQueue

public class java.awt

EventQueue

Java SE 6

EventQueue is a platform-independent class that queues events, both from the underlying peer classes and from trusted application classes.

It encapsulates asynchronous event dispatch machinery which extracts events from the queue and dispatches them by calling dispatchEvent(AWTEvent) method on this EventQueue with the event to be dispatched as an argument. The particular behavior of this machinery is implementation-dependent. The only requirements are that events which were actually enqueued to this queue (note that events being posted to the EventQueue can be coalesced) are dispatched:

Sequentially.: That is, it is not permitted that several events from this queue are dispatched simultaneously.
In the same order as they are enqueued.: That is, if AWTEvent A is enqueued to the EventQueue before AWTEvent B then event B will not be dispatched before event A.

Some browsers partition applets in different code bases into separate contexts, and establish walls between these contexts. In such a scenario, there will be one EventQueue per context. Other browsers place all applets into the same context, implying that there will be only a single, global EventQueue for all applets. This behavior is implementation-dependent. Consult your browser's documentation for more information.

For information on the threading issues of the event dispatch machinery, see AWT Threading Issues.

version 1.105, 07/11/06

since 1.1

Constructors

public

EventQueue()

Methods

protected void

dispatchEvent(AWTEvent event) Details

Dispatches an event. The manner in which the event is dispatched depends upon the type of the event and the type of the event's source object:

Event Type	Source Type	Dispatched To
ActiveEvent	Any	event.dispatch()
Other	Component	source.dispatchEvent(AWTEvent)
Other	MenuComponent	source.dispatchEvent(AWTEvent)
Other	Other	No action (ignored)

event	an instance of `java.awt.AWTEvent`, or a subclass of it
Throws	NullPointerException: if `event` is `null`
since	1.2

public static void

invokeAndWait(Runnable runnable) throws InterruptedException, InvocationTargetException Details

Causes runnable to have its run method called in the dispatch thread of the system EventQueue. This will happen after all pending events are processed. The call blocks until this has happened. This method will throw an Error if called from the event dispatcher thread.

runnable	the `Runnable` whose `run` method should be executed synchronously on the `EventQueue`
Throws	InterruptedException: if any thread has interrupted this thread
Throws	InvocationTargetException: if an throwable is thrown when running `runnable`
since	1.2
See also	invokeLater

public static void

invokeLater(Runnable runnable) Details

Causes runnable to have its run method called in the dispatch thread of the system EventQueue. This will happen after all pending events are processed.

runnable	the `Runnable` whose `run` method should be executed synchronously on the `EventQueue`
since	1.2
See also	invokeAndWait

public AWTEvent

peekEvent() Details

Returns the first event on the EventQueue without removing it.

return

the first event

public AWTEvent

peekEvent(int id) Details

Returns the first event with the specified id, if any.

id	the id of the type of event desired
return	the first event of the specified id or `null` if there is no such event

protected void

pop() throws EmptyStackException Details

Stops dispatching events using this EventQueue. Any pending events are transferred to the previous EventQueue for processing.

Warning: To avoid deadlock, do not declare this method synchronized in a subclass.

Throws EmptyStackException: if no previous push was made on this EventQueue

since 1.2

See also push

public void

postEvent(AWTEvent theEvent) Details

Posts a 1.1-style event to the EventQueue. If there is an existing event on the queue with the same ID and event source, the source Component's coalesceEvents method will be called.

theEvent	an instance of `java.awt.AWTEvent`, or a subclass of it
Throws	NullPointerException: if `theEvent` is `null`

public void

push(EventQueue newEventQueue) Details

Replaces the existing EventQueue with the specified one. Any pending events are transferred to the new EventQueue for processing by it.

newEventQueue	an `EventQueue` (or subclass thereof) instance to be use
Throws	NullPointerException: if `newEventQueue` is `null`
since	1.2
See also	pop

Properties

public static AWTEvent

getCurrentEvent() Details

Returns the the event currently being dispatched by the EventQueue associated with the calling thread. This is useful if a method needs access to the event, but was not designed to receive a reference to it as an argument. Note that this method should only be invoked from an application's event dispatching thread. If this method is invoked from another thread, null will be returned.

return	the event currently being dispatched, or null if this method is invoked on a thread other than an event dispatching thread
since	1.4

public static boolean

isDispatchThread() Details

Returns true if the calling thread is the current AWT EventQueue's dispatch thread. Use this call the ensure that a given task is being executed (or not being) on the current AWT EventDispatchThread.

return	true if running on the current AWT `EventQueue`'s dispatch thread
since	1.2

public static long

getMostRecentEventTime() Details

Returns the timestamp of the most recent event that had a timestamp, and that was dispatched from the EventQueue associated with the calling thread. If an event with a timestamp is currently being dispatched, its timestamp will be returned. If no events have yet been dispatched, the EventQueue's initialization time will be returned instead.In the current version of the JDK, only InputEvents, ActionEvents, and InvocationEvents have timestamps; however, future versions of the JDK may add timestamps to additional event types. Note that this method should only be invoked from an application's event dispatching thread. If this method is invoked from another thread, the current system time (as reported by System.currentTimeMillis()) will be returned instead.

return	the timestamp of the last `InputEvent`, `ActionEvent`, or `InvocationEvent` to be dispatched, or `System.currentTimeMillis()` if this method is invoked on a thread other than an event dispatching thread
since	1.4
See also	getWhen, getWhen, getWhen

public AWTEvent

getNextEvent() throws InterruptedException Details

Removes an event from the EventQueue and returns it. This method will block until an event has been posted by another thread.

return	the next `AWTEvent`
Throws	InterruptedException: if any thread has interrupted this thread

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Java SE 6

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