Worker Threads and SwingWorker

When a Swing program needs to execute a long-running task, it usually uses one of the worker threads, also known as the background threads. Each task running on a worker thread is represented by an instance of javax.swing.SwingWorker. SwingWorker itself is an abstract class; you must define a subclass in order to create a SwingWorker object; anonymous inner classes are often useful for creating very simple SwingWorker objects.

SwingWorker provides a number of communication and control features:

  • The SwingWorker subclass can define a method, done , which is automatically invoked on the event dispatch thread when the background task is finished.

  • SwingWorker implements java.util.concurrent.Future. This interface allows the background task to provide a return value to the other thread. Other methods in this interface allow cancellation of the background task and discovering whether the background task has finished or been cancelled.

  • The background task can provide intermediate results by invoking SwingWorker.publish , causing SwingWorker.process to be invoked from the event dispatch thread.

  • The background task can define bound properties. Changes to these properties trigger events, causing event-handling methods to be invoked on the event dispatch thread.

These features are discussed in the following subsections.

Note:

The javax.swing.SwingWorker class was added to the Java platform in Java SE 6. Prior to this, another class, also called SwingWorker , was widely used for some of the same purposes. The old SwingWorker was not part of the Java platform specification, and was not provided as part of the JDK.

The new javax.swing.SwingWorker is a completely new class. Its functionality is not a strict superset of the old SwingWorker . Methods in the two classes that have the same function do not have the same names. Also, instances of the old SwingWorker class were reusable, while a new instance of javax.swing.SwingWorker is needed for each new background task.

Throughout the Java Tutorials, any mention of SwingWorker now refers to javax.swing.SwingWorker .