updating JFrame again

Question

The following code shown below will add 3 JLabels to a JFrame and then remove the 3 JLabels. After 2 seconds it will repaint back the 3 JLabels.

import javax.swi         


        

Answer 1

1. Simpy use a CardLayout to swap views in and out.
2. Use a Swing Timer rather than your current background Thread as your current code is not Swing thread safe and carries risk of pernicious unpredictable thread exceptions.
3. I would give the main JPanel the CardLayout, and then add a JLabel holding JPanel with a suitable String constant.
4. I'd then add to the main CardLayout using JPanel, an empty JLabel using another String constant in the add method. i.e., add(new JLabel(), BLANK_COMPONENT);
5. I'd then in my Swing Timer simply call next() on my CardLayout object, passing in the main CardLayout-using component: cardLayout.next(myMainJPanel);

---

For example,

import java.awt.CardLayout;
import java.awt.Dimension;
import java.awt.event.*;

import javax.swing.*;

public class RepaintTest extends JPanel {
   private static final int PREF_W = 400;
   private static final int PREF_H = PREF_W;
   private static final int LABEL_COUNT = 3;
   private static final String LABEL_PANEL = "label panel";
   private static final Object BLANK_COMPONENT = "blank component";
   private static final int TIMER_DELAY = 2000;
   private CardLayout cardLayout = new CardLayout();

   public RepaintTest() {
      JPanel labelPanel = new JPanel();
      for (int i = 0; i < LABEL_COUNT; i++) {
         labelPanel.add(new JLabel("Label " + (i + 1)));
      }

      setLayout(cardLayout);
      add(labelPanel, LABEL_PANEL);
      add(new JLabel(), BLANK_COMPONENT);

      new Timer(TIMER_DELAY, new TimerListener()).start();

   }

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

   private class TimerListener implements ActionListener {
      @Override
      public void actionPerformed(ActionEvent e) {
         cardLayout.next(RepaintTest.this);
      }
   }

   private static void createAndShowGui() {
      RepaintTest mainPanel = new RepaintTest();

      JFrame frame = new JFrame("RepaintTest");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}