How to force calling paintComponent?

Question

I have a JLabel with the paintComponent() overriden.I want it to be forcefully called since the code that updates my Label UI is this event.How can I force its calling and updating of UI? (by the way,repaint does not work!)

here is my code :

BufferedImage background;
String Uri;

public CustomClockLabel(String Uri){
    init(Uri);
    this.Uri = Uri;
}

public void init(String Uri){
    try {
        URL inp = CustomClockLabel.class.getResource(Uri);
        background = ImageIO.read(inp);
    } catch (IOException e) {
        e.printStackTrace();
    }
}

@Override
protected void paintComponent(Graphics g){
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

    if(background != null){
        g2.drawImage(background, 0, 0,getWidth(),getHeight(), this);
    }
    g2.dispose();
    super.paintComponent(g);
}

here is the code that updates labels and it is called recursively :

lblHour1 = new CustomClockLabel("/icons/noa_en/"+Hour.charAt(0)+".png");
lblHour1.repaint();
lblHour2 = new CustomClockLabel("/icons/noa_en/"+Hour.charAt(1)+".png");
lblHour2.repaint();
lblMin1 = new CustomClockLabel("/icons/noa_en/"+Minute.charAt(0)+".png");
lblMin1.repaint();
lblMin2 = new CustomClockLabel("/icons/noa_en/"+Minute.charAt(1)+".png");
lblMin1.repaint();

Answer 1

You may be under the false impression that creating new labels will update what's on the screen, doing this...

lblHour1 = new CustomClockLabel("/icons/noa_en/"+Hour.charAt(0)+".png");
lblHour2 = new CustomClockLabel("/icons/noa_en/"+Hour.charAt(1)+".png");
lblMin1 = new CustomClockLabel("/icons/noa_en/"+Minute.charAt(0)+".png");
lblMin2 = new CustomClockLabel("/icons/noa_en/"+Minute.charAt(1)+".png");

Will change the reference of the variables, so they will no longer be the same variables as those you added to the screen.

Assuming that the above variables have being added to the screen already, you could simply update them by using something like...

lblHour1.init(new ImageIcon("/icons/noa_en/"+Hour.charAt(0)+".png"));
lblHour2.init(new ImageIcon("/icons/noa_en/"+Hour.charAt(1)+".png"));
lblMin1.init(new ImageIcon("/icons/noa_en/"+Minute.charAt(0)+".png"));
lblMin2.init(new ImageIcon("/icons/noa_en/"+Minute.charAt(1)+".png"));
revalidate();
repaint();

If that fails, you should try setting one the labels border's properties so you can see if it's actually been added to the screen.

Updated

After some experimentation with what little you code you have made available, here are some more recommendations...

1. As has already being mentioned, make sure you are calling super.paintComponent first, as one of the jobs of this method is to clear the graphics ready for painting...
2. Make sure you provide a suitable sizing hint to the component, so the layout managers have some kind of idea of how big you might like the component to be. This ensures that the component is not sized to 0x0

The following example is very simple, but takes (what little) code you supplied and builds a runnable example from it...

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class PaintComponentTest {

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

    private int time = 0;

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

                final CustomClockLabel counter = new CustomClockLabel("/icons/0.png");
                Timer timer = new Timer(1000, new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        time++;
                        if (time > 9) {
                            time = 0;
                        }
                        counter.init("/icons/" + Integer.toString(time) + ".png");
                        counter.repaint();
                    }
                });
                timer.start();

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(counter);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class CustomClockLabel extends JPanel {

        BufferedImage background;
        String Uri;

        public CustomClockLabel(String Uri) {
            init(Uri);
            this.Uri = Uri;
        }

        public void init(String Uri) {
            try {
                URL inp = getClass().getResource(Uri);
                background = ImageIO.read(inp);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(100, 100);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D) g.create();
            g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

            if (background != null) {
                g2.drawImage(background, 0, 0, getWidth(), getHeight(), this);
            }
            g2.dispose();
        }
    }

}