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Java™ Platform Standard Ed. 6 |
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java.lang.Objectjava.awt.EventQueue
public class EventQueue
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 Summary | |
|---|---|
EventQueue()
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| Method Summary | |
|---|---|
protected void |
dispatchEvent(AWTEvent event)
Dispatches an event. |
static AWTEvent |
getCurrentEvent()
Returns the 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(Runnable runnable)
Causes runnable to have its run
method called in the dispatch thread of
the system EventQueue. |
static void |
invokeLater(Runnable runnable)
Causes runnable to have its run
method called in the dispatch thread of
the system EventQueue. |
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(int id)
Returns the first event with the specified id, if any. |
protected void |
pop()
Stops dispatching events using this EventQueue. |
void |
postEvent(AWTEvent theEvent)
Posts a 1.1-style event to the EventQueue. |
void |
push(EventQueue newEventQueue)
Replaces the existing EventQueue with the specified one. |
| Methods inherited from class java.lang.Object |
|---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Constructor Detail |
|---|
public EventQueue()
| Method Detail |
|---|
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 it
NullPointerException - 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 desired
null
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 it
NullPointerException - if event is nullpublic 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 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.
InputEvent,
ActionEvent, or InvocationEvent to be
dispatched, or System.currentTimeMillis() if this
method is invoked on a thread other than an event dispatching
threadInputEvent.getWhen(),
ActionEvent.getWhen(),
InvocationEvent.getWhen()public 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 use
NullPointerException - if newEventQueue is nullpop()
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 EventQueuepush(java.awt.EventQueue)public static boolean isDispatchThread()
EventQueue's dispatch thread. Use this
call the ensure that a given
task is being executed (or not being) on the current AWT
EventDispatchThread.
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
synchronously on the EventQueueinvokeAndWait(java.lang.Runnable)
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 on the EventQueue
InterruptedException - if any thread has
interrupted this thread
InvocationTargetException - if an throwable is thrown
when running runnableinvokeLater(java.lang.Runnable)
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Java™ Platform Standard Ed. 6 |
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