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Unfreeze Your Applications with the New SwingWorker
by Dan Andrews
Poorly-written Swing applications can appear to freeze when time-consuming code is executing. These applications frequently fail to provide their users with feedback on the code's execution state. In the worst case, end users will wonder if the application is working correctly.
This unresponsiveness happens because all Swing applications handle events on the event dispatch thread. This means painting, layout updates, button presses, rollover effects, and Swing component interactions. When this kind of time-consuming code is executed on the event dispatch thread, all other-event driven activity waits and the application appears frozen.
A Possible Solution
A solution to the frozen application problem usually begins by moving time-consuming code to a background thread. Both synchronous and asynchronous communication can be used to inform the event dispatch thread of the code's execution state (see Listing 1).
The code in Listing 1 is not complex, but it is error prone. You might type thread.run() instead of thread.start(). In that case, your application would continue to exhibit the frozen behavior—and possibly other unexpected behaviors. Typing thread.run() in this case would be an easy error to detect, but only because it is a serious error to use invokeAndWait on the event dispatch thread. So this solution isn't really all that effective. Additionally, the code in Listing 1 is several lines long and there is no way to easily reuse it.
A Reusable Solution
The original SwingWorker, which was never included in the JDK, was written as reusable way to move time-consuming code to a background thread. In May of 1998, SwingWorker was posted in a Sun Microsystems' article about threads and Swing. For eight years SwingWorker existed in this limbo state. An Internet search for the terms "SwingWorker" and "Direct Known SubClasses" locates many publicly documented versions of SwingWorker. The original has been widely adopted. It has also been modified and incorporated into various corporate infrastructures.
On December 11, 2006, the Java SE 6 platform was officially released and with it, a complete rewrite of the javax.swing.SwingWorker became available to Java developers. Including the SwingWorker in a JDK has been a huge improvement. You can now refer to the SwingWorker class and everyone can be sure the reference is to the javax.swing.SwingWorker. Hopefully, usage examples of the SwingWorker in Java SE 6 platform will begin to be more consistent and familiar to programmers and its usage will increase.
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