EventQueue (Java 2 Platform SE v1.4.1)

java.awt
Class EventQueue
java.lang.Object
  |
  +--java.awt.EventQueue
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:

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.

Since:

1.1

Constructor Summary
EventQueue()


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 EventQueue.
static void invokeLater(Runnable runnable)
    Causes runnable to have its run method called in the dispatch thread of the 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

EventQueue
public EventQueue()
Method Detail

postEvent
public void postEvent(AWTEvent theEvent)
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.

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

getNextEvent
public AWTEvent getNextEvent()
                      throws InterruptedException
Removes an event from the EventQueue and returns it. This method will block until an event has been posted by another thread.

Returns:
the next AWTEvent
Throws:
InterruptedException - if another thread has interrupted this thread

peekEvent
public AWTEvent peekEvent()
Returns the first event on the EventQueue without removing it.

Returns:
the first event

peekEvent
public 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 null if there is no such event

dispatchEvent
protected 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 Type Source Type Dispatched To

ActiveEvent Any event.dispatch()

Other Component source.dispatchEvent(AWTEvent)

Other MenuComponent source.dispatchEvent(AWTEvent)

Other Other No action (ignored)

Throws:
NullPointerException - if event is null

getMostRecentEventTime
public 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. 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 Java platform SDK, only InputEvents, ActionEvents, and InvocationEvents have timestamps; however, future versions of the SDK 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.

Returns:
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:
InputEvent.getWhen(), ActionEvent.getWhen(), InvocationEvent.getWhen()

getCurrentEvent
public static AWTEvent getCurrentEvent()
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.

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

push
public void push(EventQueue newEventQueue)
Replaces the existing EventQueue with the specified one. Any pending events are transferred to the new EventQueue for processing by it.

Parameters:
newEventQueue - an EventQueue (or subclass thereof) instance to be use
Throws:
NullPointerException - if newEventQueue is null
See Also:
pop()

pop
protected void pop()
            throws EmptyStackException
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
See Also:
push(java.awt.EventQueue)

isDispatchThread
public static boolean isDispatchThread()
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.

Returns:
true if running on the current AWT EventQueue's dispatch thread

invokeLater
public static void invokeLater(Runnable runnable)
Causes runnable to have its run method called in the dispatch thread of the EventQueue. This will happen after all pending events are processed.

Parameters:
runnable - the Runnable whose run method should be executed synchronously on the EventQueue
Since:

1.2

See Also:
invokeAndWait(java.lang.Runnable)

invokeAndWait
public static void invokeAndWait(Runnable runnable)
                          throws InterruptedException,
                                 InvocationTargetException
Causes runnable to have its run method called in the dispatch thread of the 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.

Parameters:
runnable - the Runnable whose run method should be executed synchronously on the EventQueue
Throws:
InterruptedException - if another thread has interrupted this thread
InvocationTargetException - if an exception is thrown when running runnable
Since:

1.2

See Also:
invokeLater(java.lang.Runnable)

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 EventQueue.
static void	invokeLater(Runnable runnable) Causes runnable to have its run method called in the dispatch thread of the 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.

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)

java.awt Class EventQueue

Constructor Summary

Method Summary

Constructor Detail

EventQueue

Method Detail

postEvent

getNextEvent

peekEvent

peekEvent

dispatchEvent

getMostRecentEventTime

getCurrentEvent

push

pop

isDispatchThread

invokeLater

invokeAndWait

java.awt
Class EventQueue