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javaswingevent-dispatch-threadprintlnswingutilities

Does system.out.println have to be on edt?

I was running some code that did a printout in a swingworker. I was not getting printouts so I used SwingUtilities.invokeLater and now it works. I did not expect this result, how did this happen? I would have thought System.out.println could run outside of the EDT.

Solution

  • That would have been pretty easy to test (not to say, even typing all the code to test this is less work then posting it here):

    import java.awt.EventQueue;
public class HelloWorld {
  public static void main( String[] args ) {
    System.out.println("Hello world");
    System.out.println( EventQueue.isDispatchThread());
  }
}

    results in 

    Hello world
false

    on the console.

    So yes, System.out.println can be used outside the EDT