SwingWorker is useful when a time-consuming task has to be performed following a user-interaction event. The most straightforward way to do it is : private Document doc; ... JButton button = new JButton; button.addActionListener;
This will work, but unfortunately, the loadXML method will be called in the same thread as the main Swing thread, so if the method needs time to perform, the GUI will freeze during this time.
SwingWorker solution
This problem is not specific to Java, but common to many GUI models. SwingWorker proposes a way to solve it by performing the time-consuming task on another background thread, keeping the GUI responsive during this time.
Creating the worker
The following code defines the SwingWorker, which encapsulates the loadXMLmethod call : SwingWorker worker = new SwingWorker ;
The result can be retrieved by using the ' method. As calling ' on the Event Dispatch Thread blocks all events, including repaints, from being processed until the task completes, one must avoid calling it before the lengthy operation has finished. There are two ways to retrieve the result after the task completion :
override the ' method. This method is called on the main event dispatching thread.
private Document doc; ... SwingWorker worker = new SwingWorker
register a listener by using the worker ' method. The listener will be notified of changes in the worker state.
Complete Worker example
private Document doc; ... JButton button = new JButton; button.addActionListener;
History: Usage before Java 6.0
SwingWorker has been part of Java SE only since Java 6.0. Sun has released versions to be used with earlier JDKs, although they were unofficial versions which were not part of the Java SE and were not mentioned in the standard library documentation. The most recent of these versions dates from 2003 and is often referred to as SwingWorker version 3. Unfortunately, the JDK 6.0 SwingWorker and the Version 3 SwingWorker use different method names and are not compatible. The backport version is now recommended for pre-Java 6 usage. An example for instantiating SwingWorker 3 is shown below: SwingWorker worker = new SwingWorker ; worker.start; //Start the background thread
The start method executes the code added in the construct method in a separate thread. To be alerted when the background thread finishes, one need only override the finished method. The construct method can return a result which can later be retrieved using SwingWorker's get method.
Backport of the Java 6 SwingWorker
A backport of the Java 6 SwingWorker to Java 5 is available at http://swingworker.java.net/. Apart from the package name, it is compatible with the Java 6 SwingWorker.
