public class EventQueue extends Object
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:
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.
Constructor | Description |
---|---|
EventQueue() |
Initializes a new instance of EventQueue . |
Modifier and Type | Method | Description |
---|---|---|
SecondaryLoop |
createSecondaryLoop() |
Creates a new secondary loop associated with this event queue. |
protected void |
dispatchEvent |
Dispatches an event. |
static AWTEvent |
getCurrentEvent() |
Returns the event currently being dispatched by the EventQueue associated with the calling thread. |
static long |
getMostRecentEventTime() |
Returns the timestamp of the most recent event that had a timestamp, and that was dispatched from the EventQueue associated with the calling thread. |
AWTEvent |
getNextEvent() |
Removes an event from the EventQueue and returns it. |
static void |
invokeAndWait |
|
static void |
invokeLater |
|
static boolean |
isDispatchThread() |
Returns true if the calling thread is the current AWT EventQueue 's dispatch thread. |
AWTEvent |
peekEvent() |
Returns the first event on the EventQueue without removing it. |
AWTEvent |
peekEvent |
Returns the first event with the specified id, if any. |
protected void |
pop() |
Stops dispatching events using this EventQueue . |
void |
postEvent |
Posts a 1.1-style event to the EventQueue . |
void |
push |
Replaces the existing EventQueue with the specified one. |
public EventQueue()
EventQueue
.public void postEvent(AWTEvent theEvent)
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 itNullPointerException
- if theEvent
is null
public AWTEvent getNextEvent() throws InterruptedException
EventQueue
and returns it. This method will block until an event has been posted by another thread.AWTEvent
InterruptedException
- if any thread has interrupted this threadpublic AWTEvent peekEvent()
EventQueue
without removing it.public AWTEvent peekEvent(int id)
id
- the id of the type of event desirednull
if there is no such eventprotected void dispatchEvent(AWTEvent event)
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 itNullPointerException
- if event
is null
public static long getMostRecentEventTime()
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 InputEvent
s, ActionEvent
s, and InvocationEvent
s 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.InputEvent
, ActionEvent
, or InvocationEvent
to be dispatched, or System.currentTimeMillis()
if this method is invoked on a thread other than an event dispatching threadpublic static AWTEvent getCurrentEvent()
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.public void push(EventQueue newEventQueue)
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 useNullPointerException
- if newEventQueue
is null
protected void pop() throws EmptyStackException
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.
EmptyStackException
- if no previous push was made on this EventQueue
public SecondaryLoop createSecondaryLoop()
secondary loop
associated with this event queue. Use the SecondaryLoop.enter()
and SecondaryLoop.exit()
methods to start and stop the event loop and dispatch the events from this queue.public static boolean isDispatchThread()
the 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)
or invokeAndWait(java.lang.Runnable)
methods to execute a task in the current AWT EventQueue
's dispatch thread.
the current AWT EventQueue
's dispatch threadpublic static void invokeLater(Runnable runnable)
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 asynchronously in the event dispatch thread
of the system EventQueue
public static void invokeAndWait(Runnable runnable) throws InterruptedException, InvocationTargetException
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 in the event dispatch thread
of the system EventQueue
InterruptedException
- if any thread has interrupted this threadInvocationTargetException
- if an throwable is thrown when running runnable
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
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https://docs.oracle.com/en/java/javase/21/docs/api/java.desktop/java/awt/EventQueue.html