Java EventQueue. Why should everything be in invokelater method?

Question

in the book that i'm reading, every example of GUI with multithreading has something like that:

public static void main(String[] args) throws Exception
{
    EventQueue.invokeLater(new Runnable()
    {
        public void run()
        {
            JFrame frame = new SomeKindOfFrame();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);
        }
    });
}

(i mean EventQueue). but isn't the code automatically executed in the main (EDT) thread?

Congruence

Answer 1

Desktop GUI applications usually work in this way. There is one thread for gui and one or several threads for rest of application. Using EventQueue you specify what GUI thread should do from other threads.

Deforce

Apparently in swing this is called the "single thread rule". Swing events are proccesed from the event thread which takes these little Runnable() instances and runs them. – Concordia

@Warren P, totally agree. I just tried to explain this in the easiest way. BTW, thanks for grammar corrections. – Deforce

Answer 2

The main thread isn't the same as the EDT. If you add System.out.println(Thread.currentThread().getName() you'll see it print out main within main() and AWT-EventQueue-0 when within the run() method of the Runnable.

Here is a discussion of the history of the single threaded rule in Swing that might help make things clearer.

Pylos