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The '''event dispatching thread''' (EDT) is a background [[Thread (computer science)|thread]] used in [[Java programming language|Java]] to process events from the [[Abstract Windowing Toolkit]] (AWT) [[graphical user interface]] [[event queue]]. These events are primarily update events that cause user interface [[Software componentry|components]] to redraw themselves, or input events from [[input device]]s such as the mouse or keyboard. The AWT uses a single-threaded painting [[Model (abstract)|model]] in which all screen updates must be performed from a single thread. The event dispatching thread is the only valid thread to update the visual state of visible user interface components. Updating visible components from other threads is the source of many common [[Software bug|bugs]] in Java [[Computer program|programs]] that use [[Swing (Java)|Swing]].
== Executing code in the EDT ==
Other application threads can execute code in the event dispatching thread by defining the code in a {{Javadoc:SE|java/lang|Runnable}} object and pass it to the {{Javadoc:SE|javax/swing|SwingUtilities}} helper class or to the {{Javadoc:SE|java/awt|EventQueue}}. Two methods of these classes allow synchronous ({{Javadoc:SE|member=invokeAndWait(Runnable)|javax/swing|SwingUtilities|invokeAndWait(java.lang.Runnable)}} or {{Javadoc:SE|member=invokeAndWait(Runnable)|java/awt|EventQueue|invokeAndWait(java.lang.Runnable)}}) and asynchronous ({{Javadoc:SE|member=invokeLater(Runnable)|javax/swing|SwingUtilities|invokeLater(java.lang.Runnable)}} or {{Javadoc:SE|member=invokeLater(Runnable)|java/awt|EventQueue|invokeLater(java.lang.Runnable)}}) code execution from the EDT. The method <code>invokeAndWait()</code> should never be called from the event dispatching thread—it will throw an [[Exception handling|exception]]. The method {{Javadoc:SE|javax/swing|SwingUtilities|isEventDispatchThread()}} or {{Javadoc:SE|java/awt|EventQueue|isEventDispatchThread()}} can be called to determine if the current thread is the event dispatching thread.
Another solution for executing code in the EDT is using the ''[[Worker pattern|worker design pattern]]''. The <code>[[SwingWorker]]</code> class, developed by [[Sun Microsystems]], is an implementation of the worker design pattern, but is not a part of standard Swing distribution. The open source project [http://foxtrot.sourceforge.net/ Foxtrot] provides another synchronous execution solution similar to <code>SwingWorker</code>.
== See also ==
* [[Abstract Windowing Toolkit]]
* [[Swing (Java)]]
== External links ==
* {{Javadoc:SE|package=javax.swing|javax/swing}} (Swing API [[Javadoc]] documentation)
* {{Javadoc:SE|package=java.awt|java/awt}} (AWT API [[Javadoc]] documentation)
* {{Javadoc:SE-guide|swing|Swing API documentation}}
* {{Javadoc:SE-guide|awt|AWT API documentation}}
* [http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html#EDT The Event-Dispatching Thread]
* [http://java.sun.com/docs/books/tutorial/uiswing/misc/example-1dot4/SwingWorker.java SwingWorker] class source code
* [http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html#SwingWorker SwingWorker] description from the Swing tutorial
* [http://foxtrot.sourceforge.net/ Foxtrot project home page]
* [http://www.swingwiki.org/other:swing_threading Swing multithreading issues] article on SwingWiki.org, containing descriptions and workarounds for several problems caused by EDT misuse
* [http://www.swingwiki.org/best:use_worker_thread_for_long_operations Use worker thread for long operations] article on SwingWiki.org, containing code examples for SwingWorker and Foxtrot
[[Category:Java programming language]]
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