In computer programming, a utility class is a class that defines a set of methods that perform common, often re-used functions. Most utility classes define these common methods under static scope...
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
Swing is the primary Java GUI widget toolkit. It is part of Oracle's Java Foundation Classes — an API for providing a graphical user interface for Java programs....
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
The event dispatching thread is a background thread used in Java to process events from the Abstract Window Toolkit graphical user interface event queue. These events are primarily update events that cause user interface components to redraw themselves, or input events from input devices such as...
. As of Java 6, is included in the JRE.
Several incompatible, unofficial, versions of SwingWorker were produced from 1998 to 2006, and care must be taken to avoid the abundant documentation on these versions predating Java 6.
The event dispatching thread problem
SwingWorker is useful when a time-consuming task has to be performed following a user-interaction event (for example, parsing a huge XML File, on pressing a JButton). The most straightforward way to do it is :
private Document doc;
...
JButton button = new JButton("Open XML");
button.addActionListener(new ActionListener {
public void actionPerformed(ActionEvent e) {
doc = loadXML;
}
});
This will work, but unfortunately, the loadXML method will be called in the same thread
Thread (computer science)
In computer science, a thread of execution is the smallest unit of processing that can be scheduled by an operating system. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process...
The event dispatching thread is a background thread used in Java to process events from the Abstract Window Toolkit graphical user interface event queue. These events are primarily update events that cause user interface components to redraw themselves, or input events from input devices such as...
), so if the method needs time to perform, the GUI
Graphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
will freeze during this time.
SwingWorker solution
This problem is not specific to Java, but common to many GUI
Graphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
models. SwingWorker proposes a way to solve it by performing the time-consuming task on another background thread, keeping the GUI
Graphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
responsive during this time.
Creating the worker
The following code defines the SwingWorker, which encapsulates the loadXML method call :
SwingWorker worker = new SwingWorker {
public Document doInBackground {
Document intDoc = loadXML;
return intDoc;
}
};
Worker execution
Execution is started by using the
method.
Retrieving the result
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 :
The event dispatching thread is a background thread used in Java to process events from the Abstract Window Toolkit graphical user interface event queue. These events are primarily update events that cause user interface components to redraw themselves, or input events from input devices such as...
SwingWorker has only been part of JSE 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 J2SE 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 (see below) is now recommended for pre-Java 6 usage.
An example for instantiating SwingWorker 3 is shown below:
SwingWorker worker = new SwingWorker {
public Object construct {
... //add the code for the background thread
}
public void finished {
... //code that you add here will run in the UI thread
}
};
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 only needs to 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 has been available at https://swingworker.dev.java.net/ since March 2007. Apart from the package name ( org.jdesktop.swingworker ), it is compatible with the Java 6 SwingWorker.
swingLabs is a Sun open source project proposing extensions to the Java Swing GUI toolkit. Available components include:* Sorting, filtering, highlighting for tables, trees, and lists* Find/search* Auto-completion* Login/authentication framework...
The .NET Framework is a software framework that runs primarily on Microsoft Windows. It includes a large library and supports several programming languages which allows language interoperability...
