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

public class AnimatedJList extends JList 
    implements ListSelectionListener {

    static java.util.Random rand = new java.util.Random();

    static Color listForeground, listBackground,
        listSelectionForeground, listSelectionBackground;
    static float[] foregroundComps, backgroundComps,
        foregroundSelectionComps, backgroundSelectionComps;

    static {
        UIDefaults uid = UIManager.getLookAndFeel().getDefaults();
        listForeground =  uid.getColor ("List.foreground");
        listBackground =  uid.getColor ("List.background");
        listSelectionForeground =  uid.getColor ("List.selectionForeground");
        listSelectionBackground =  uid.getColor ("List.selectionBackground");
        foregroundComps =
            listForeground.getRGBColorComponents(null);
        foregroundSelectionComps = 
            listSelectionForeground.getRGBColorComponents(null);
        backgroundComps =
            listBackground.getRGBColorComponents(null);
        backgroundSelectionComps =
            listSelectionBackground.getRGBColorComponents(null);
    }
    public Color colorizedSelectionForeground,
        colorizedSelectionBackground;

    public static final int ANIMATION_DURATION = 500;
    public static final int ANIMATION_REFRESH = 50;

    public AnimatedJList() {
        super();
        addListSelectionListener (this);
        setCellRenderer (new AnimatedCellRenderer());
    }

    public void valueChanged (ListSelectionEvent lse) {
        if (! lse.getValueIsAdjusting()) {
            HashSet selections = new HashSet();
            // System.out.println ("got last lse");
            for (int i=0; i < getModel().getSize(); i++) {
                if (getSelectionModel().isSelectedIndex(i))
                    selections.add (new Integer(i));
            }
            CellAnimator animator = new CellAnimator (selections.toArray());
            animator.start();
        }
    }

    public static void main (String[] args) {
        JList list = new AnimatedJList ();
        DefaultListModel defModel = new DefaultListModel();
        list.setModel (defModel);
        String[] listItems = {
            "Chris", "Joshua", "Daniel", "Michael",
            "Don", "Kimi", "Kelly", "Keagan"
        };
        Iterator it = Arrays.asList(listItems).iterator();
        while (it.hasNext())
            defModel.addElement (it.next());
        // show list
        JScrollPane scroller =
            new JScrollPane (list,
                            ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,
                            ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
        JFrame frame = new JFrame ("Checkbox JList");
        frame.getContentPane().add (scroller);
        frame.pack();
        frame.setVisible(true);
    }

    class CellAnimator extends Thread {
        Object[] selections;
        long startTime;
        long stopTime;
        public CellAnimator (Object[] s) {
            selections = s;
        }
        public void run() {
            startTime = System.currentTimeMillis();
            stopTime = startTime + ANIMATION_DURATION;
            while (System.currentTimeMillis() < stopTime) {
                colorizeSelections();
                repaint();
                try { Thread.sleep (ANIMATION_REFRESH); } 
                catch (InterruptedException ie) {}
            }
            // one more, at 100% selected color
            colorizeSelections();
            repaint();
        }
        public void colorizeSelections() {
            // calculate % completion relative to start/stop times
            float elapsed = (float) (System.currentTimeMillis() - startTime);
            float completeness = Math.min ((elapsed/ANIMATION_DURATION), 1.0f);
            // System.out.println ("completeness = " + completeness);
            // calculate scaled color
            float colorizedForeComps[] = new float[3];
            float colorizedBackComps[] = new float[3];
            for (int i=0; i<3; i++) {
                colorizedForeComps[i] =
                    foregroundComps[i] +
                    (completeness * 
                     (foregroundSelectionComps[i] - foregroundComps[i]));
                colorizedBackComps[i] =
                    backgroundComps[i] +
                    (completeness * 
                     (backgroundSelectionComps[i] - backgroundComps[i]));
            }
            colorizedSelectionForeground =
                new Color (colorizedForeComps[0],
                           colorizedForeComps[1],
                           colorizedForeComps[2]);
            colorizedSelectionBackground =
                new Color (colorizedBackComps[0],
                           colorizedBackComps[1],
                           colorizedBackComps[2]);
            // System.out.println ("fore = " +colorizedSelectionForeground);
            // System.out.println ("back = " +colorizedSelectionBackground);
        }
    }

    class AnimatedCellRenderer extends DefaultListCellRenderer {
        public Component getListCellRendererComponent(JList list,
                                                      Object value,
                                                      int index,
                                                      boolean isSelected,
                                                      boolean hasFocus) {
            Component returnMe =
                super.getListCellRendererComponent (list, value, index,
                                                    isSelected, hasFocus);
            if (isSelected) {
                returnMe.setForeground (colorizedSelectionForeground);
                returnMe.setBackground (colorizedSelectionBackground);
                /* this might be necessary if you have more
                   elaborate cells
                if (returnMe instanceof Container) {
                    Component[] children =
                        ((Container)returnMe).getComponents ();
                    System.out.println (children.length + " children");
                    for (int i=0;
                         (children != null ) && (i<children.length);
                         i++) {
                        children[i].setForeground (colorizedSelectionForeground);
                    children[i].setBackground (colorizedSelectionBackground);
                    }
                }
                */
                if (returnMe instanceof JComponent)
                    ((JComponent) returnMe).setOpaque(true);
            }
            return returnMe;
        }
    }
}