Java: I can't run JTextArea multiple times?

Question

Hello and welcome everyone, this is my first question so I hope that it is a good one. I was exploring the swing API and I came across a question that popped in my head. I b

Answer 1

Welcome to blocking the Event Dispatching Thread.

The EDT is responsible, for among other things, processing repainting requests. You should never performing any operations that block the EDT, instead, you should using something like a SwingWorker

Take a look at Concurrency in Swing for more details

Updated with example

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingWorker;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestTextArea03 {

    public static void main(String[] args) {
        new TestTextArea03();
    }

    public TestTextArea03() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        });
    }

    public class TestPane extends JPanel {

        private JTextArea textArea;

        private TestPane() {
            setLayout(new BorderLayout());
            textArea = new JTextArea(10, 10);
            add(new JScrollPane(textArea));

            new TextWorker().execute();
        }

        public class TextWorker extends SwingWorker<Void, String> {

            @Override
            protected void process(List<String> chunks) {
                for (String text : chunks) {
                    textArea.append(text + "\n");
                }
            }

            @Override
            protected Void doInBackground() throws Exception {
                Thread.sleep(1000);
                for (int x = 0; x < 10; x++) {
                    publish(String.valueOf(x));
                    Thread.sleep(250);
                }
                return null;
            }

        }

    }

}

Or a Swing Timer

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingWorker;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestTextArea03 {

    public static void main(String[] args) {
        new TestTextArea03();
    }

    public TestTextArea03() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        });
    }

    public class TestPane extends JPanel {

        private JTextArea textArea;
        private int x;

        private TestPane() {
            setLayout(new BorderLayout());
            textArea = new JTextArea(10, 10);
            add(new JScrollPane(textArea));

            Timer timer = new Timer(250, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    x++;
                    textArea.append(String.valueOf(x) + "\n");
                }
            });
            timer.setRepeats(true);
            timer.setCoalesce(true);
            timer.start();
        }        
    }    
}