Tutorials : Unfreeze Your Applications with the New SwingWorker :

Important Method Signatures

• The cancel Method: This takes a boolean parameter. If you want to kill your time-consuming code, invoking cancel(true) is SwingWorker object's equivalent of a kill -9. If you would prefer to have your time-consuming code cancel more gracefully, use cancel(false). The return value will be true if cancel was successful; however, a false value may indicate the time-consuming code has already completed or been canceled.

  public boolean cancel(boolean mayInterruptIfRunning);
  

• The isCancelled Method: Use this method if you are using the graceful form of cancel. It is left up to your time-consuming code to periodically check if it should cancel gracefully (e.g. while(!done && !isCancelled){...} where done is local to your implementation).

  public boolean isCancelled();
  

• The Get Methods: If your time-consuming code is returning a result then you will need to retrieve it using one of the SwingWorker object's get methods. ]
  • If you invoke get before your time-consuming code is done, then get will block it, so don't do that if you are on the event dispatch thread.

    public final T get() throws InterruptedException, ExecutionException;
    
    public final T get(long timeout, TimeUnit unit) throws 
      InterruptedException, ExecutionException, TimeoutException;(also a bullet) 
    

  • The second form of the get method allows you to specify a timeout and would be useful if your time-consuming code is permanently waiting on a failed resource. Being able to invoke get on a background thread and having it block until the time-consuming code has completed is another demonstration of the SwingWorker object's flexibility, but most of the time you will invoke get after the SwingWorker is done and there is one thing you need to know.

• The done Method: When you are informed that the SwingWorker is done via a property change or via the SwingWorker object's done method, you need to be aware that the get methods can throw a CancellationException. A CancellationException is a RuntimeException, which means you do not need to declare it thrown and you do not need to catch it. Instead, you should test the SwingWorker using the isCancelled method before you use the get method.

Built for the Future

Dan Andrews is the President of Ansir Development Limited. He has been a Sun Certified Programmer for the Java(tm) 2 Platform since 1999. Prior to founding Ansir Development Limited in 2005, Dan worked at SED Systems as a programmer analyst. At SED, he worked on building large Swing applications which help control some of the world's largest satellite networks and deep space antennas.

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