Why the Images in a JComponent are not drawn properly at loading?

Question

Why does the initializeGameField() function not consistently load images when this program runs? Sometimes it shows no image bound to the JLabel, and sometimes it shows all 9 images correctly. I have printed the image path to verify that it is correct. How can I implement the drag and drop feature to the added images?

package game;    
import java.awt.Color;
import java.awt.Cursor;
import java.awt.Dimension;
import java.awt.Panel;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.net.URL;    
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JLayeredPane;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingConstants;
import javax.swing.event.MouseInputAdapter;

public class NMMPanel {    
    private JFrame frame;
    private int appWidth = 728;
    private int appHeigth = 828;

    private JPanel topButtonPanel, topLeftPanel, topRightPanel; // main
    private JLayeredPane centerPanel;
    private JTextArea txtLogArea;
    private JButton btnNewButton, btnQuitButton;

    private JPanel user1Panel, user2Panel; // sub panels for user1 and user2
    private JLabel chessBoardLabel, stateLabel;

    private JTextField name1TextField, name2TextField;
    private JDialog newGameDialog;
    private boolean turnOfStarter = true;

    private JLabel[] blacks = null;
    private JLabel[] whites = null;

    private Node[] nodes = new Node[24];

    /**
     * Constructor: components and variables setup.
     */
    public NMMPanel() {
        initializeWindow();
        initializeGameField();
    }

    private void initializeWindow() {
        Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
        frame = new JFrame();
        frame.setResizable(false);
        frame.setBounds((dim.width / 2 - (appWidth / 2)),
                (dim.height / 2 - (appHeigth / 2)), appWidth, appHeigth);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);

        frame.setTitle("9MM - Nine Men's Morris");

        topButtonPanel = new JPanel();
        topButtonPanel.setBounds(6, 0, 710, 36);
        btnNewButton = new JButton("New");
        btnQuitButton = new JButton("Quit");
        topButtonPanel.add(btnNewButton);
        topButtonPanel.add(btnQuitButton);
        frame.getContentPane().add(topButtonPanel);

        // Add listeners to buttons.
        ButtonListener listenToButton = new ButtonListener();
        btnNewButton.addActionListener(listenToButton);
        btnQuitButton.addActionListener(listenToButton);

        topLeftPanel = new JPanel();
        topLeftPanel.setForeground(new Color(0, 0, 0));
        topLeftPanel.setBackground(new Color(255, 255, 204));
        topLeftPanel.setBounds(6, 35, 352, 100);
        frame.getContentPane().add(topLeftPanel);
        topLeftPanel.setLayout(null);

        topRightPanel = new JPanel();
        topRightPanel.setBackground(Color.DARK_GRAY);
        topRightPanel.setBounds(364, 35, 350, 100);
        frame.getContentPane().add(topRightPanel);
        topRightPanel.setLayout(null);

        centerPanel = new JLayeredPane();
        centerPanel.setBackground(Color.ORANGE);
        centerPanel.setBounds(118, 140, 500, 500);
        frame.getContentPane().add(centerPanel);
        centerPanel.setLayout(null);

        ImageIcon field = createImageIcon("/resources/Spielfeld_roundedCorners.png");
        JLabel feld = new JLabel(field);
        feld.setBounds(0, 0, 500, 500);
        centerPanel.add(feld, 2);

        ImageIcon texture = createImageIcon("/resources/Wood.jpg");
        JLabel textureCenter = new JLabel(texture);
        textureCenter.setBounds(0, 0, 500, 500);
        centerPanel.add(textureCenter, 3);

        setupEventFields(24);

        JScrollPane scrollPane = new JScrollPane();
        scrollPane.setBounds(6, 645, 710, 149);
        frame.getContentPane().add(scrollPane);

        txtLogArea = new JTextArea();
        txtLogArea.setEditable(false);
        scrollPane.setViewportView(txtLogArea);

        if (turnOfStarter) {
            txtLogArea.append("Whites turn!\n");
        } else {
            txtLogArea.append("Blacks turn!\n");
        }
        frame.setVisible(true);
    }

    private void setupEventFields(int counter) {
        initNodes();
        for (int i = 0; i < counter; i++) {
            final JLabel interactionFields = new JLabel("FFFF");
            interactionFields.setHorizontalAlignment(SwingConstants.CENTER);
            interactionFields.setBounds(nodes[i].location.x,
                    nodes[i].location.y, 50, 50);
            interactionFields.setCursor(Cursor
                    .getPredefinedCursor(Cursor.HAND_CURSOR));

            // TODO : Remove later
            interactionFields.setForeground(new Color(255, 255, 255));

            interactionFields.addMouseListener(new MouseAdapter() {
                @Override
                public void mouseEntered(MouseEvent e) {
                    System.out.println("entered here");
                    System.out.println(interactionFields.getLocation());
                }

                @Override
                public void mouseClicked(MouseEvent e) {
                    System.out.println("Clicked here");

                }

            });
            centerPanel.add(interactionFields, 0);
        }
    }

    private void initNodes() {
        int x = 10;
        int y = 10;
        nodes[0] = new Node("O_0", x, y);

        x = 225;
        y = 10;
        nodes[1] = new Node("O_1", x, y);

        x = 440;
        y = 10;
        nodes[2] = new Node("O_2", x, y);

        x = 74;
        y = 74;
        nodes[3] = new Node("M_0", x, y);

        x = 225;
        y = 72;
        nodes[4] = new Node("M_1", x, y);

        x = 376;
        y = 74;
        nodes[5] = new Node("M_2", x, y);

        x = 137;
        y = 135;
        nodes[6] = new Node("I_0", x, y);

        x = 225;
        y = 135;
        nodes[7] = new Node("I_1", x, y);

        x = 314;
        y = 136;
        nodes[8] = new Node("I_2", x, y);

        x = 10;
        y = 225;
        nodes[9] = new Node("O_3", x, y);

        x = 72;
        y = 225;
        nodes[10] = new Node("M_3", x, y);

        x = 135;
        y = 225;
        nodes[11] = new Node("I_3", x, y);

        x = 316;
        y = 225;
        nodes[12] = new Node("I_4", x, y);

        x = 378;
        y = 225;
        nodes[13] = new Node("M_4", x, y);

        x = 440;
        y = 225;
        nodes[14] = new Node("O_4", x, y);

        x = 137;
        y = 313;
        nodes[15] = new Node("I_5", x, y);

        x = 225;
        y = 316;
        nodes[16] = new Node("I_6", x, y);

        x = 314;
        y = 314;
        nodes[17] = new Node("I_7", x, y);

        x = 74;
        y = 375;
        nodes[18] = new Node("M_5", x, y);

        x = 225;
        y = 377;
        nodes[19] = new Node("M_6", x, y);

        x = 376;
        y = 376;
        nodes[20] = new Node("M_7", x, y);

        x = 10;
        y = 440;
        nodes[21] = new Node("O_5", x, y);

        x = 225;
        y = 440;
        nodes[22] = new Node("O_6", x, y);

        x = 440;
        y = 440;
        nodes[23] = new Node("O_7", x, y);
    }

    protected Node getNode(Point location) {
        for (int i = 0; i < nodes.length; i++) {
            if ((nodes[i].location.x == location.x)
                    && (nodes[i].location.y == location.y)) {
                return nodes[i];
            }
        }
        return null;
    }

    /** Returns an ImageIcon, or null if the path was invalid. */
    protected ImageIcon createImageIcon(String path) {
        URL imgURL = getClass().getResource(path);
        if (imgURL != null) {
            return new ImageIcon(imgURL);
        } else {
            System.err.println("Couldn't find file: " + path);
            return null;
       }
    }

    private void initializeGameField() {
        ImageIcon iconWhite = createImageIcon("/resources/White_Stone.png");
        int space = 10;
        blacks = new JLabel[9];
        whites = new JLabel[9];

        JLabel lblPlayer1 = new JLabel("PLAYER 1");
        lblPlayer1.setBounds(150, 80, 61, 16);
        topLeftPanel.add(lblPlayer1);

        for (int i = 0; i < 9; i++) {
            final JLabel lblWhite = new JLabel(iconWhite);
            lblWhite.addMouseListener(new MouseAdapter() {

                @Override
                public void mouseClicked(MouseEvent e) {
                    System.out.println("Clicked");
                }

                @Override
                public void mouseDragged(MouseEvent e) {
                    System.out.println("Dragged");
                }

                @Override
                public void mouseMoved(MouseEvent e) {
                    System.out.println("Moved");
                }

                @Override
                public void mousePressed(MouseEvent e) {
                    System.out.println("Pressed");
                }

                @Override
                public void mouseReleased(MouseEvent e) {
                    System.out.println("Released");

                }
            });

            lblWhite.setBounds(space, 25, 50, 50);
            topLeftPanel.add(lblWhite);
            space += 35;
            whites[i] = lblWhite;
        }

        JLabel lblPlayer2 = new JLabel("PLAYER 2");
        lblPlayer2.setForeground(new Color(255, 255, 255));
        lblPlayer2.setBounds(150, 80, 61, 16);
        topRightPanel.add(lblPlayer2);

        ImageIcon iconBlack = createImageIcon("/resources/Black_Stone.png");

        space = 10;
        for (int j = 0; j < 9; j++) {
            final JLabel lblBlack = new JLabel(iconBlack);
            lblBlack.addMouseListener(new MouseAdapter() {
                @Override
                public void mouseClicked(MouseEvent e) {

                }

                @Override
                public void mouseDragged(MouseEvent e) {
                    System.out.println("Dragged");
                }

                @Override
                public void mouseMoved(MouseEvent e) {
                    System.out.println("Moved");
                }

                @Override
                public void mousePressed(MouseEvent e) {
                    System.out.println("Pressed");
                }

                @Override
                public void mouseReleased(MouseEvent e) {
                    System.out.println("Released");
                    super.mouseReleased(e);
                }
            });

            lblBlack.setBounds(space, 25, 50, 50);
            topRightPanel.add(lblBlack);
            space += 35;
            blacks[j] = lblBlack;
            System.out.println(lblBlack);
        }
    }
}

Answer 1

The intermittent nature of the problem suggests a threading issue.

Are you calling the constructor new NMMPanel(); from the Swing event dispatch thread? Otherwise, you might be creating all the components from a different thread. Since Swing methods are not thread safe, you might be creating labels (with icons) while the image icon loading is part-complete.

Normally, the JLabel will set itself as the ImageIcon's ImageObserver, so that it can receive a message to repaint itself once the images are loaded. If the modifications are not on the event thread, this might not happen.

---

edit:

public static void main(String[] args) { // Set up the frame and add the panel.   
    SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        NMMPanel panel = new NMMPanel(); 
      } 
    }
 }