Question

I’m trying to write a Java applet that will display a user-inputted String, it should then flash the string by switching between that and another one. I’m trying to use a thread to do this, but I’m new to those and Applets, I don’t know what to do from here on out.

here’s what I have so far:

public class FlashingLabel extends JApplet implements Runnable
{
String blank;
String input;
JLabel label; 
Thread t;



public void init() 
{
    input = JOptionPane.showInputDialog(null, "Enter String", "Flashing Label",   JOptionPane.QUESTION_MESSAGE);
    blank=" ";

    t=new Thread(this);
    t.start();
}

public void run() 
{
    while(true)
    {
        label=new JLabel(blank);
        add(label);
        this.repaint();
        label=new JLabel(input);
        add(label);
        this.repaint();
    }
}
}

Answer 1

• Never do anything within the Event Dispatching Thread that will block it (long running tasks or IO), it will make your application look like it’s hung.
• Never create or update any UI component from any thread other then the Event Dispatching Thread
• There’s no need create new JLabels each time you want to update the message, simple use JLabel#setText. You’re code is currently adding two new labels on each loop through

For you’re needs, a simple javax.swing.Timer will perform the task you are trying to achieve.

public class FlashApplet extends JApplet {

    @Override
    public void init() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                setLayout(new BorderLayout());
                add(new FlashPane());

            }
        });
    }

    @Override
    public void start() {
    }

    public static class FlashPane extends JPanel {

        protected static final String[] MESSAGES = {"Bad Boys", "What you gonna do"};

        private Timer flashTimer;
        private JLabel label;
        private int messageIndex = -1;

        public FlashPane() {
            setLayout(new BorderLayout());
            add((label = new JLabel()));
            label.setHorizontalAlignment(JLabel.CENTER);

            flashTimer = new Timer(500, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    messageIndex++;
                    if (messageIndex >= MESSAGES.length) {
                        messageIndex = 0;
                    }
                    label.setText(MESSAGES[messageIndex]);
                }
            });
            flashTimer.setRepeats(true);
            flashTimer.setCoalesce(true);
            flashTimer.setInitialDelay(0);
            flashTimer.start();
        }

    }

}

You might like to have a read through Concurrency in Swing