Java: CustomComboBoxDemo

package components;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

/*
 * CustomComboBoxDemo.java uses the following files:
 *   images/Bird.gif
 *   images/Cat.gif
 *   images/Dog.gif
 *   images/Rabbit.gif
 *   images/Pig.gif
 */
public class CustomComboBoxDemo extends JPanel {
  ImageIcon[] images;
  String[] petStrings = {"Bird", "Cat", "Dog", "Rabbit", "Pig"};

  /*
   * Despite its use of EmptyBorder, this panel makes a fine content
   * pane because the empty border just increases the panel's size
   * and is "painted" on top of the panel's normal background.  In
   * other words, the JPanel fills its entire background if it's
   * opaque (which it is by default); adding a border doesn't change
   * that.
   */
  public CustomComboBoxDemo() {
    super(new BorderLayout());

    //Load the pet images and create an array of indexes.
    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]);
      }
    }

    //Create the combo box.
    JComboBox petList = new JComboBox(intArray);
    ComboBoxRenderer renderer= new ComboBoxRenderer();
    renderer.setPreferredSize(new Dimension(200, 130));
    petList.setRenderer(renderer);
    petList.setMaximumRowCount(3);

    //Lay out the demo.
    add(petList, BorderLayout.PAGE_START);
    setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
  }

  /** Returns an ImageIcon, or null if the path was invalid. */
  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;
    }
  }

  /**
   * Create the GUI and show it.  For thread safety,
   * this method should be invoked from the
   * event-dispatching thread.
   */
  private static void createAndShowGUI() {
    //Create and set up the window.
    JFrame frame = new JFrame("CustomComboBoxDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Create and set up the content pane.
    JComponent newContentPane = new CustomComboBoxDemo();
    newContentPane.setOpaque(true); //content panes must be opaque
    frame.setContentPane(newContentPane);

    //Display the window.
    frame.pack();
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    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);
    }

    /*
     * This method finds the image and text corresponding
     * to the selected value and returns the label, set up
     * to display the text and image.
     */
    public Component getListCellRendererComponent(
      JList list,
      Object value,
      int index,
      boolean isSelected,
      boolean cellHasFocus) {
      //Get the selected index. (The index param isn't
      //always valid, so just use the value.)
      int selectedIndex = ((Integer)value).intValue();

      if (isSelected) {
        setBackground(list.getSelectionBackground());
        setForeground(list.getSelectionForeground());
      } else {
        setBackground(list.getBackground());
        setForeground(list.getForeground());
      }

      //Set the icon and text.  If icon was null, say so.
      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;
    }

    //Set the font and text when no image was found.
    protected void setUhOhText(String uhOhText, Font normalFont) {
      if (uhOhFont == null) { //lazily create this font
        uhOhFont = normalFont.deriveFont(Font.ITALIC);
      }
      setFont(uhOhFont);
      setText(uhOhText);
    }
  }
}