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Concurrency in Swing
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 completly 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.
