multithreading - Java/Swing Print text from a child thread

Question

I have a swing Frame displayed, with a button to start a thread :

public class Frame extends JFrame {
    private static Frame frame= null;
    public static Frame getFrame(){
        return frame== null? frame= new Frame(): frame;
    }

    Thread worker;
    JTextArea  textarea = new JTextArea();
    JButton b = new JButton();

    Frame(){
        frameinstance = this;
        b.addActionListener(actionEvent -> {
            worker = new Thread(new myWorker());
            worker.start();
        });
        //...
    }
}

The thread looks like :

public class myWorker implements Runnable {
    public void run(){
        //Do some work
        Frame.getFrame().textArea.append("Some work has been done");
        //Do some work
       Frame.getFrame().textArea.append("Some work has been done");
        //etc...
    }

}

But the text actually does not appears as work progress.

Answer 1

Swing components should only be updated on the event dispatch thread. Most Swing components are not thread-safe and updating them in other threads can have unpredictable behavior.

You can use SwingUtilities.invokeLater (to schedule the update and continue) or SwingUtilities.invokeAndWait (to block until the event is processed) to update the UI.

For example:

 SwingUtilities.invokeLater(()->Frame.getFrame().textArea.append("Some work has been done"));