Java: IconDemoApp

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Component;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.Icon;

/**
 * The "missing icon" is a white box with a black border and a red x. It's used
 * to display something when there are issues loading an icon from an external
 * location.
 *
 */
public class MissingIcon implements Icon {

    private int width = 32;
    private int height = 32;

    private BasicStroke stroke = new BasicStroke(4);

    @Override
    public void paintIcon(Component c, Graphics g, int x, int y) {
        Graphics2D g2d = (Graphics2D) g.create();

        g2d.setColor(Color.WHITE);
        g2d.fillRect(x + 1, y + 1, width - 2, height - 2);

        g2d.setColor(Color.BLACK);
        g2d.drawRect(x + 1, y + 1, width - 2, height - 2);

        g2d.setColor(Color.RED);

        g2d.setStroke(stroke);
        g2d.drawLine(x + 10, y + 10, x + width - 10, y + height - 10);
        g2d.drawLine(x + 10, y + height - 10, x + width - 10, y + 10);

        g2d.dispose();
    }

    @Override
    public int getIconWidth() {
        return width;
    }

    @Override
    public int getIconHeight() {
        return height;
    }

}

import java.awt.BorderLayout;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.image.BufferedImage;
import java.util.List;
import javax.swing.AbstractAction;
import javax.swing.BorderFactory;
import javax.swing.Box;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JToolBar;
import javax.swing.SwingUtilities;
import javax.swing.SwingWorker;

/**
 * This application is intended to demonstrate the loading of image files into
 * icons for use in a Swing user interface. It creates a toolbar with a
 * thumbnail preview of each image. Clicking on the thumbnail will show the full
 * image in the main display area.
 *
 * IconDemoApp.java requires the following files: <br>
 * The following files are copyright 2006 spriggs.net and licensed under a
 * Creative Commons License (http://creativecommons.org/licenses/by-sa/3.0/)
 * <br>
 * public/images/article/sunw01.jpg <br>
 * public/images/article/sunw02.jpg <br>
 * public/images/article/sunw03.jpg <br>
 * public/images/article/sunw04.jpg <br>
 * public/images/article/sunw05.jpg <br>
 *
 * @author Collin Fagan
 * @date 7/25/2007
 * @version 2.0
 */
public class IconDemoApp extends JFrame {

    private JLabel photographLabel = new JLabel();
    private JToolBar buttonBar = new JToolBar();

    private String imagedir = "public/images/article/";

    private MissingIcon placeholderIcon = new MissingIcon();

    /**
     * List of all the descriptions of the image files. These correspond one to
     * one with the image file names
     */
    private String[] imageCaptions = {"Original SUNW Logo", "The Clocktower",
        "Clocktower from the West", "The Mansion", "Sun Auditorium"};

    /**
     * List of all the image files to load.
     */
    private String[] imageFileNames = {"sunw01.jpg", "sunw02.jpg",
        "sunw03.jpg", "sunw04.jpg", "sunw05.jpg"};

    /**
     * Main entry point to the demo. Loads the Swing elements on the "Event
     * Dispatch Thread".
     *
     * @param args
     */
    public static void main(String args[]) {
        SwingUtilities.invokeLater(() -> {
            IconDemoApp app = new IconDemoApp();
            app.setVisible(true);
        });
    }

    /**
     * Default constructor for the demo.
     */
    public IconDemoApp() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setTitle("Icon Demo: Please Select an Image");

        // A label for displaying the pictures
        photographLabel.setVerticalTextPosition(JLabel.BOTTOM);
        photographLabel.setHorizontalTextPosition(JLabel.CENTER);
        photographLabel.setHorizontalAlignment(JLabel.CENTER);
        photographLabel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));

        // We add two glue components. Later in process() we will add thumbnail buttons
        // to the toolbar inbetween thease glue compoents. This will center the
        // buttons in the toolbar.
        buttonBar.add(Box.createGlue());
        buttonBar.add(Box.createGlue());

        add(buttonBar, BorderLayout.SOUTH);
        add(photographLabel, BorderLayout.CENTER);

        setSize(400, 300);

        // this centers the frame on the screen
        setLocationRelativeTo(null);

        // start the image loading SwingWorker in a background thread
        loadpublic/images/article.execute();
    }

    /**
     * SwingWorker class that loads the public/images/article a background thread and calls
     * publish when a new one is ready to be displayed.
     *
     * We use Void as the first SwingWroker param as we do not need to return
     * anything from doInBackground().
     */
    private SwingWorker<Void, ThumbnailAction> loadpublic/images/article = new SwingWorker<Void, ThumbnailAction>() {

        /**
         * Creates full size and thumbnail versions of the target image files.
         */
        @Override
        protected Void doInBackground() throws Exception {
            for (int i = 0; i < imageCaptions.length; i++) {
                ImageIcon icon;
                icon = createImageIcon(imagedir + imageFileNames[i], imageCaptions[i]);

                ThumbnailAction thumbAction;
                if (icon != null) {

                    ImageIcon thumbnailIcon = new ImageIcon(getScaledImage(icon.getImage(), 32, 32));

                    thumbAction = new ThumbnailAction(icon, thumbnailIcon, imageCaptions[i]);

                } else {
                    // the image failed to load for some reason
                    // so load a placeholder instead
                    thumbAction = new ThumbnailAction(placeholderIcon, placeholderIcon, imageCaptions[i]);
                }
                publish(thumbAction);
            }
            // unfortunately we must return something, and only null is valid to
            // return when the return type is void.
            return null;
        }

        /**
         * Process all loaded public/images/article.
         */
        @Override
        protected void process(List<ThumbnailAction> chunks) {
            for (ThumbnailAction thumbAction : chunks) {
                JButton thumbButton = new JButton(thumbAction);
                // add the new button BEFORE the last glue
                // this centers the buttons in the toolbar
                buttonBar.add(thumbButton, buttonBar.getComponentCount() - 1);
            }
        }
    };

    /**
     * Creates an ImageIcon if the path is valid.
     *
     * @param String - resource path
     * @param String - description of the file
     */
    protected ImageIcon createImageIcon(String path,
            String description) {
        java.net.URL imgURL = getClass().getResource(path);
        if (imgURL != null) {
            return new ImageIcon(imgURL, description);
        } else {
            System.err.println("Couldn't find file: " + path);
            return null;
        }
    }

    /**
     * Resizes an image using a Graphics2D object backed by a BufferedImage.
     *
     * @param srcImg - source image to scale
     * @param w - desired width
     * @param h - desired height
     * @return - the new resized image
     */
    private Image getScaledImage(Image srcImg, int w, int h) {
        BufferedImage resizedImg = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = resizedImg.createGraphics();
        g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
        g2.drawImage(srcImg, 0, 0, w, h, null);
        g2.dispose();
        return resizedImg;
    }

    /**
     * Action class that shows the image specified in it's constructor.
     */
    private class ThumbnailAction extends AbstractAction {

        /**
         * The icon if the full image we want to display.
         */
        private Icon displayPhoto;

        /**
         * @param Icon - The full size photo to show in the button.
         * @param Icon - The thumbnail to show in the button.
         * @param String - The descriptioon of the icon.
         */
        public ThumbnailAction(Icon photo, Icon thumb, String desc) {
            displayPhoto = photo;

            // The short description becomes the tooltip of a button.
            putValue(SHORT_DESCRIPTION, desc);

            // The LARGE_ICON_KEY is the key for setting the
            // icon when an Action is applied to a button.
            putValue(LARGE_ICON_KEY, thumb);
        }

        /**
         * Shows the full image in the main area and sets the application title.
         */
        @Override
        public void actionPerformed(ActionEvent e) {
            photographLabel.setIcon(displayPhoto);
            setTitle("Icon Demo: " + getValue(SHORT_DESCRIPTION).toString());
        }
    }
}