how can i have a delay on my interface (java swing) using Java Swing Timer?

Question

i'm new to Java and I'm trying to add a time delay when I press a Jbutton start. I used TimeUnit.SECONDS.sleep() but it didn't work, then i researched and found out about java swing timer, but it didn't work either and I can't figure out why

btnStart.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
              Timer timer = new Timer(1000, new ActionListener() {
                 @Override
                 public void actionPerformed(ActionEvent e) {
                     System.out.println("start DONE");          
                     Object step;
                     for (int i = 1; i < n; i++) {                         
                       //code that shows on interface
                       // then i want a delay here then to carry on with the iteration of for
                       timer.start();
                       };
                 }
             });
         }
     });

Answer 1

You're almost there. But you seem to be misunderstanding what the Timer is actually doing for you.

The Timer is acting as a kind of pseudo loop, with a built in delay. That is, after each time period, it will execute. This means, that each time your ActionListener is triggered, you want to execute the next step in your logic.

For example...

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.Timer;

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

    public Main() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private JPanel contentPane = new JPanel(new GridBagLayout());

        public TestPane() {
            setLayout(new BorderLayout());
            add(new JScrollPane(contentPane));

            JButton startButton = new JButton("Start");
            startButton.addActionListener(new ActionListener() {
                private int row = 0;
                private int count = 1000;
                private DateTimeFormatter formatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
                @Override
                public void actionPerformed(ActionEvent e) {
                    row = 0;
                    GridBagConstraints gbc = new GridBagConstraints();
                    gbc.gridwidth = gbc.REMAINDER;
                    gbc.weightx = 1;
                    contentPane.removeAll();
                    contentPane.revalidate();
                    contentPane.repaint();

                    Timer timer = new Timer(100, new ActionListener() {
                        @Override
                        public void actionPerformed(ActionEvent e) {
                            row++;
                            if (row >= count) {
                                ((Timer)(e.getSource())).stop();
                                return;
                            }

                            JLabel label = new JLabel(LocalDateTime.now().format(formatter));
                            contentPane.add(label, gbc);
                            contentPane.revalidate();
                            contentPane.repaint();
                            // This is only required because the layout pass seems
                            // to be execute in different run cycle, so the label's
                            // bounds are not been updated yet.  We force the layout
                            // pass so we can scroll to the label, but otherwise
                            // isn't needed
                            contentPane.doLayout();
                            Rectangle bounds = label.getBounds();
                            bounds.y += bounds.height;
                            contentPane.scrollRectToVisible(bounds);
                        }
                    });
                    timer.start();
                }
            });
            add(startButton, BorderLayout.NORTH);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }
    }
}