- java.lang.Object
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- java.awt.EventQueue
 
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 public class EventQueue extends Object EventQueueis 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 thisEventQueuewith 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 theEventQueuecan 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 AWTEventA is enqueued to theEventQueuebeforeAWTEventB 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 EventQueueper context. Other browsers place all applets into the same context, implying that there will be only a single, globalEventQueuefor 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. - Since:
- 1.1
 
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Constructor SummaryConstructors Constructor Description EventQueue()Initializes a new instance ofEventQueue.
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Method SummaryAll Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description SecondaryLoopcreateSecondaryLoop()Creates a newsecondary loopassociated with this event queue.protected voiddispatchEvent(AWTEvent event)Dispatches an event.static AWTEventgetCurrentEvent()Returns the event currently being dispatched by theEventQueueassociated with the calling thread.static longgetMostRecentEventTime()Returns the timestamp of the most recent event that had a timestamp, and that was dispatched from theEventQueueassociated with the calling thread.AWTEventgetNextEvent()Removes an event from theEventQueueand returns it.static voidinvokeAndWait(Runnable runnable)static voidinvokeLater(Runnable runnable)static booleanisDispatchThread()Returns true if the calling thread isthe current AWT EventQueue's dispatch thread.AWTEventpeekEvent()Returns the first event on theEventQueuewithout removing it.AWTEventpeekEvent(int id)Returns the first event with the specified id, if any.protected voidpop()Stops dispatching events using thisEventQueue.voidpostEvent(AWTEvent theEvent)Posts a 1.1-style event to theEventQueue.voidpush(EventQueue newEventQueue)Replaces the existingEventQueuewith the specified one.
 
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Method Detail- 
postEventpublic void postEvent(AWTEvent theEvent) Posts a 1.1-style event to theEventQueue. If there is an existing event on the queue with the same ID and event source, the sourceComponent'scoalesceEventsmethod will be called.- Parameters:
- theEvent- an instance of- java.awt.AWTEvent, or a subclass of it
- Throws:
- NullPointerException- if- theEventis- null
 
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getNextEventpublic AWTEvent getNextEvent() throws InterruptedException Removes an event from theEventQueueand returns it. This method will block until an event has been posted by another thread.- Returns:
- the next AWTEvent
- Throws:
- InterruptedException- if any thread has interrupted this thread
 
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peekEventpublic AWTEvent peekEvent() Returns the first event on theEventQueuewithout removing it.- Returns:
- the first event
 
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peekEventpublic AWTEvent peekEvent(int id) Returns the first event with the specified id, if any.- Parameters:
- id- the id of the type of event desired
- Returns:
- the first event of the specified id or nullif there is no such event
 
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dispatchEventprotected void dispatchEvent(AWTEvent event) 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 types, source types, and dispatch methods 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) - Parameters:
- event- an instance of- java.awt.AWTEvent, or a subclass of it
- Throws:
- NullPointerException- if- eventis- null
- Since:
- 1.2
 
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getMostRecentEventTimepublic static long getMostRecentEventTime() Returns the timestamp of the most recent event that had a timestamp, and that was dispatched from theEventQueueassociated 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, onlyInputEvents,ActionEvents, andInvocationEvents 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'sevent dispatching thread. If this method is invoked from another thread, the current system time (as reported bySystem.currentTimeMillis()) will be returned instead.- Returns:
- the timestamp of the last InputEvent,ActionEvent, orInvocationEventto be dispatched, orSystem.currentTimeMillis()if this method is invoked on a thread other than an event dispatching thread
- Since:
- 1.4
- See Also:
- InputEvent.getWhen(),- ActionEvent.getWhen(),- InvocationEvent.getWhen(),- isDispatchThread()
 
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getCurrentEventpublic static AWTEvent getCurrentEvent() Returns the event currently being dispatched by theEventQueueassociated 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.- Returns:
- the event currently being dispatched, or null if this method is invoked on a thread other than an event dispatching thread
- Since:
- 1.4
 
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pushpublic void push(EventQueue newEventQueue) Replaces the existingEventQueuewith the specified one. Any pending events are transferred to the newEventQueuefor processing by it.- Parameters:
- newEventQueue- an- EventQueue(or subclass thereof) instance to be use
- Throws:
- NullPointerException- if- newEventQueueis- null
- Since:
- 1.2
- See Also:
- pop()
 
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popprotected void pop() throws EmptyStackExceptionStops dispatching events using thisEventQueue. Any pending events are transferred to the previousEventQueuefor 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(java.awt.EventQueue)
 
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createSecondaryLooppublic SecondaryLoop createSecondaryLoop() Creates a newsecondary loopassociated with this event queue. Use theSecondaryLoop.enter()andSecondaryLoop.exit()methods to start and stop the event loop and dispatch the events from this queue.- Returns:
- secondaryLoop A new secondary loop object, which can be used to launch a new nested event loop and dispatch events from this queue
- Since:
- 1.7
- See Also:
- SecondaryLoop.enter(),- SecondaryLoop.exit()
 
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isDispatchThreadpublic static boolean isDispatchThread() Returns true if the calling thread isthe current AWT EventQueue's dispatch thread. Use this method to ensure that a particular task is being executed (or not being) there.Note: use the invokeLater(java.lang.Runnable)orinvokeAndWait(java.lang.Runnable)methods to execute a task inthe current AWT EventQueue's dispatch thread.- Returns:
- true if running in
 the current AWT EventQueue's dispatch thread
- Since:
- 1.2
- See Also:
- invokeLater(java.lang.Runnable),- invokeAndWait(java.lang.Runnable),- Toolkit.getSystemEventQueue()
 
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invokeLaterpublic static void invokeLater(Runnable runnable) Causesrunnableto have itsrunmethod called in thedispatch threadofthe system EventQueue. This will happen after all pending events are processed.- Parameters:
- runnable- the- Runnablewhose- runmethod should be executed asynchronously in the- event dispatch threadof- the system EventQueue
- Since:
- 1.2
- See Also:
- invokeAndWait(java.lang.Runnable),- Toolkit.getSystemEventQueue(),- isDispatchThread()
 
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invokeAndWaitpublic static void invokeAndWait(Runnable runnable) throws InterruptedException, InvocationTargetException Causesrunnableto have itsrunmethod called in thedispatch threadofthe 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 theevent dispatcher thread.- Parameters:
- runnable- the- Runnablewhose- runmethod should be executed synchronously in the- event dispatch threadof- the system EventQueue
- Throws:
- InterruptedException- if any thread has interrupted this thread
- InvocationTargetException- if an throwable is thrown when running- runnable
- Since:
- 1.2
- See Also:
- invokeLater(java.lang.Runnable),- Toolkit.getSystemEventQueue(),- isDispatchThread()
 
 
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