Swingworker do in background method does not caught and print exceptions?

David Holmes David.Holmes at oracle.com
Mon Sep 27 22:26:38 UTC 2010


Paulo Levi said the following on 09/28/10 04:23:
> In in linux 64 bits.
> java version "1.6.0_20"
> OpenJDK Runtime Environment (IcedTea6 1.9) (6b20-1.9-0ubuntu1)
> OpenJDK 64-Bit Server VM (build 17.0-b16, mixed mode)
> from ubuntu repositories.
> A very simple swingworker started from the EDT:
>         new SwingWorker<Object, Object>() {
>             @Override
>             protected Object doInBackground() throws Exception {
>                 System.out.println("SW Ran");
>                 throw new NullPointerException();
>             }
>         }.run();
> Only prints SW Ran.
> It's surprising this was not noticed.

SwingWorker is a RunnableFuture. The exception will be caught and stored 
for retrieval via the Future methods. Trying add a get() to the above 
and it will throw the ExecutionException:

Exception in thread "main" java.util.concurrent.ExecutionException: 
         at java.util.concurrent.FutureTask.get(FutureTask.java:111)
         at javax.swing.SwingWorker.get(SwingWorker.java:601)
         at SW.main(SW.java:16)
Caused by: java.lang.NullPointerException
         at SW$1.doInBackground(SW.java:11)
         at javax.swing.SwingWorker$1.call(SwingWorker.java:296)
         at java.util.concurrent.FutureTask.run(FutureTask.java:166)
         at javax.swing.SwingWorker.run(SwingWorker.java:335)
         at SW.main(SW.java:14)

David Holmes

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