Question

Activity:

1. Build a simple GUI application using a JCombo box and images.
2. Use of a GUI Builder is prohibited.
3. Download the image file, it provides images and a framework of the code (incomplete code).
4. The lab requires two classes
   1. ComboBoxTest - provided
   2. ComboBoxFrame - partially provided
      1. Constructor -
         1. set the Frame layout type - FlowLayout is fine, but any layout type is acceptable
         2. Creates JComboBox from array of image names
         3. Creates an inner class
            1. handles the JComboBox events
            2. Displays correct image in the classes JLabel
            3. NOTE: get and image use new ImageIcon( getClass().getResource( selection ), where selection is the image file's name.
      2. You may break this into methods if you like or do all the work in the constructor.
      3. See examples ComboBoxWindow and MyCatImage in the additional example downloads as need.
5. This lab can be completed using the standard ActionListeners however, it can also be completed using the ItemListener class. If you feel adventurous, explore the API and/or other resources and use the ItemListener class.
6. Make sure you Javadoc your classes.

Answer 1

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Font;

import javax.swing.BorderFactory;
import javax.swing.ImageIcon;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.ListCellRenderer;
class CustomComboBoxDemo extends JPanel {
    ImageIcon[] images;
    String[] petStrings = {"Bird", "Cat", "Dog", "Rabbit", "Pig"};
    public CustomComboBoxDemo() {
        super(new BorderLayout());
        images = new ImageIcon[petStrings.length];
        Integer[] intArray = new Integer[petStrings.length];
        for (int i = 0; i < petStrings.length; i++) {
            intArray[i] = new Integer(i);
            images[i] = createImageIcon("images/" + petStrings[i] + ".gif");
            if (images[i] != null) {
                images[i].setDescription(petStrings[i]);
            }
        }

        JComboBox petList = new JComboBox(intArray);
        ComboBoxRenderer renderer= new ComboBoxRenderer();
        renderer.setPreferredSize(new Dimension(200, 130));
        petList.setRenderer(renderer);
        petList.setMaximumRowCount(3);
        add(petList, BorderLayout.PAGE_START);
        setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
    }
    protected static ImageIcon createImageIcon(String path) {
        java.net.URL imgURL = CustomComboBoxDemo.class.getResource(path);
        if (imgURL != null) {
            return new ImageIcon(imgURL);
        } else {
            System.err.println("Couldn't find file: " + path);
                return null;
        }
    }

    private static void createAndShowGUI() {
        JFrame.setDefaultLookAndFeelDecorated(true);
        JFrame frame = new JFrame("CustomComboBoxDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JComponent newContentPane = new CustomComboBoxDemo();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);
        frame.pack();
        frame.setVisible(true);
    }

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

    class ComboBoxRenderer extends JLabel
                           implements ListCellRenderer {
        private Font uhOhFont;

        public ComboBoxRenderer() {
            setOpaque(true);
            setHorizontalAlignment(CENTER);
            setVerticalAlignment(CENTER);
        }
        public Component getListCellRendererComponent(
                                           JList list,
                                           Object value,
                                           int index,
                                           boolean isSelected,
                                           boolean cellHasFocus) {
            int selectedIndex = ((Integer)value).intValue();

            if (isSelected) {
                setBackground(list.getSelectionBackground());
                setForeground(list.getSelectionForeground());
            } else {
                setBackground(list.getBackground());
                setForeground(list.getForeground());
            }
            ImageIcon icon = images[selectedIndex];
            String pet = petStrings[selectedIndex];
            setIcon(icon);
            if (icon != null) {
                setText(pet);
                setFont(list.getFont());
            } else {
                setUhOhText(pet + " (no image available)",
                            list.getFont());
            }

            return this;
        }
        protected void setUhOhText(String uhOhText, Font normalFont) {
            if (uhOhFont == null) { //lazily create this font
                uhOhFont = normalFont.deriveFont(Font.ITALIC);
            }
            setFont(uhOhFont);
            setText(uhOhText);
        }
    }
}