/*
 * @(#)MediaTracker.java	1.34 01/11/29
 *
 * Copyright 2002 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.awt;

import java.awt.Component;
import java.awt.Image;
import java.awt.Graphics;
import java.awt.image.ImageObserver;

/**
 * The <code>MediaTracker</code> class is a utility class to track 
 * the status of a number of media objects. Media objects could 
 * include audio clips as well as images, though currently only 
 * images are supported. 
 * <p>
 * To use a media tracker, create an instance of  
 * <code>MediaTracker</code> and call its <code>addImage</code>  
 * method for each image to be tracked. In addition, each image can 
 * be assigned a unique identifier. This identifier controls the 
 * priority order in which the images are fetched. It can also be used 
 * to identify unique subsets of the images that can be waited on 
 * independently. Images with a lower ID are loaded in preference to 
 * those with a higher ID number. 
 * <p>
 * Here is an example: 
 * <p>
 * <hr><blockquote><pre>
 * import java.applet.Applet;
 * import java.awt.Color;
 * import java.awt.Image;
 * import java.awt.Graphics;
 * import java.awt.MediaTracker;
 *
 * public class ImageBlaster extends Applet implements Runnable {
 *	MediaTracker tracker;
 *	Image bg;
 *	Image anim[] = new Image[5];
 *	int index;
 *	Thread animator;
 *
 *	// Get the images for the background (id == 0) 
 *	// and the animation frames (id == 1) 
 *      // and add them to the MediaTracker
 *	public void init() {
 *	    tracker = new MediaTracker(this);
 *	    bg = getImage(getDocumentBase(), 
 *                  "images/background.gif");
 *	    tracker.addImage(bg, 0);
 *	    for (int i = 0; i < 5; i++) {
 *		anim[i] = getImage(getDocumentBase(), 
 *                      "images/anim"+i+".gif");
 *		tracker.addImage(anim[i], 1);
 *	    }
 *	}
 *
 *	// Start the animation thread.
 *	public void start() {
 *	    animator = new Thread(this);
 *	    animator.start();
 *	}
 *
 *	// Stop the animation thread.
 *	public void stop() {
 *	    animator = null;
 *	}
 *
 *	// Run the animation thread.
 *	// First wait for the background image to fully load 
 *      // and paint.  Then wait for all of the animation 
 *	// frames to finish loading. Finally, loop and 
 *	// increment the animation frame index.
 *	public void run() {
 *	    try {
 *		tracker.waitForID(0);
 *		tracker.waitForID(1);
 *	    } catch (InterruptedException e) {
 *		return;
 *	    }
 *	    Thread me = Thread.currentThread();
 *	    while (animator == me) {
 *		try {
 *		    Thread.sleep(100);
 *		} catch (InterruptedException e) {
 *		    break;
 *		}
 *		synchronized (this) {
 *		    index++;
 *		    if (index >= anim.length) {
 *			index = 0;
 *		    }
 *		}
 *		repaint();
 *	    }
 *	}
 *
 *	// The background image fills the frame so we 
 *	// don't need to clear the applet on repaints. 
 *      // Just call the paint method.
 *	public void update(Graphics g) {
 *	    paint(g);
 *	}
 *
 *	// Paint a large red rectangle if there are any errors 
 *	// loading the images.  Otherwise always paint the 
 *	// background so that it appears incrementally as it 
 *      // is loading.  Finally, only paint the current animation 
 *	// frame if all of the frames (id == 1) are done loading,
 *	// so that we don't get partial animations.
 *	public void paint(Graphics g) {
 *	    if ((tracker.statusAll(false) & MediaTracker.ERRORED) != 0) {
 *		g.setColor(Color.red);
 *		g.fillRect(0, 0, size().width, size().height);
 *		return;
 *	    }
 *	    g.drawImage(bg, 0, 0, this);
 *	    if (tracker.statusID(1, false) == MediaTracker.COMPLETE) {
 *		g.drawImage(anim[index], 10, 10, this);
 *	    }
 *	}
 * }
 * </pre></blockquote><hr>
 * <p>
 * @version 	1.34, 11/29/01
 * @author 	Jim Graham
 * @since       JDK1.0
 */
public class MediaTracker implements java.io.Serializable {
    
    /**
     * A given Component that will be
     * tracked by a media tracker where the image will
     * eventually be drawn.
     *
     * @serial
     * @see MediaTracker()
     */
    Component target;
    /**
     * The head of the list of Images that is being
     * tracked by the MediaTracker.
     *
     * @serial
     * @see addImage()
     * @see removeImage()
     */
    MediaEntry head;

    /*
     * JDK 1.1 serialVersionUID 
     */
    private static final long serialVersionUID = -483174189758638095L;

    /**
     * Creates a media tracker to track images for a given component.
     * @param     comp the component on which the images 
     *                     will eventually be drawn.
     */
    public MediaTracker(Component comp) {
	target = comp;
    }

    /**
     * Adds an image to the list of images being tracked by this media 
     * tracker. The image will eventually be rendered at its default 
     * (unscaled) size. 
     * @param     image   the image to be tracked.
     * @param     id      an identifier used to track this image.
     */
    public void addImage(Image image, int id) {
	addImage(image, id, -1, -1);
    }

    /**
     * Adds a scaled image to the list of images being tracked  
     * by this media tracker. The image will eventually be 
     * rendered at the indicated width and height.
     * @param     image   the image to be tracked.
     * @param     id   an identifier that can be used to track this image.
     * @param     w    the width at which the image is rendered.
     * @param     h    the height at which the image is rendered.
     */
    public synchronized void addImage(Image image, int id, int w, int h) {
	head = MediaEntry.insert(head,
				 new ImageMediaEntry(this, image, id, w, h));
    }

    /**
     * Flag indicating some media is currently being loaded.
     * @see         java.awt.MediaTracker#statusAll
     * @see         java.awt.MediaTracker#statusID
     */
    public static final int LOADING = 1;

    /**
     * Flag indicating that the downloading of some media was aborted.
     * @see         java.awt.MediaTracker#statusAll
     * @see         java.awt.MediaTracker#statusID
     */
    public static final int ABORTED = 2;

    /**
     * Flag indicating that the downloading of some media encountered 
     * an error.
     * @see         java.awt.MediaTracker#statusAll
     * @see         java.awt.MediaTracker#statusID
     */
    public static final int ERRORED = 4;

    /**
     * Flag indicating that the downloading of media was completed 
     * successfully.
     * @see         java.awt.MediaTracker#statusAll
     * @see         java.awt.MediaTracker#statusID
     */
    public static final int COMPLETE = 8;

    static final int DONE = (ABORTED | ERRORED | COMPLETE);

    /**
     * Checks to see if all images being tracked by this media tracker 
     * have finished loading. 
     * <p>
     * This method does not start loading the images if they are not 
     * already loading. 
     * <p>
     * If there is an error while loading or scaling an image, then that 
     * image is considered to have finished loading. Use the 
     * <code>isErrorAny</code> or <code>isErrorID</code> methods to 
     * check for errors. 
     * @return      <code>true</code> if all images have finished loading, 
     *                       have been aborted, or have encountered 
     *                       an error; <code>false</code> otherwise.
     * @see         java.awt.MediaTracker#checkAll(boolean)
     * @see         java.awt.MediaTracker#checkID
     * @see         java.awt.MediaTracker#isErrorAny
     * @see         java.awt.MediaTracker#isErrorID
     */
    public boolean checkAll() {
	return checkAll(false, true);
    }

    /**
     * Checks to see if all images being tracked by this media tracker 
     * have finished loading. 
     * <p>
     * If the value of the <code>load</code> flag is <code>true</code>, 
     * then this method starts loading any images that are not yet 
     * being loaded. 
     * <p>
     * If there is an error while loading or scaling an image, that 
     * image is considered to have finished loading. Use the 
     * <code>isErrorAny</code> and <code>isErrorID</code> methods to 
     * check for errors. 
     * @param       load   if <code>true</code>, start loading any 
     *                       images that are not yet being loaded.
     * @return      <code>true</code> if all images have finished loading, 
     *                       have been aborted, or have encountered 
     *                       an error; <code>false</code> otherwise.
     * @see         java.awt.MediaTracker#checkID
     * @see         java.awt.MediaTracker#checkAll()
     * @see         java.awt.MediaTracker#isErrorAny()
     * @see         java.awt.MediaTracker#isErrorID(int)
     */
    public boolean checkAll(boolean load) {
	return checkAll(load, true);
    }

    private synchronized boolean checkAll(boolean load, boolean verify) {
	MediaEntry cur = head;
	boolean done = true;
	while (cur != null) {
	    if ((cur.getStatus(load, verify) & DONE) == 0) {
		done = false;
	    }
	    cur = cur.next;
	}
	return done;
    }

    /**
     * Checks the error status of all of the images.
     * @return   <code>true</code> if any of the images tracked
     *                  by this media tracker had an error during 
     *                  loading; <code>false</code> otherwise.
     * @see      java.awt.MediaTracker#isErrorID
     * @see      java.awt.MediaTracker#getErrorsAny
     */
    public synchronized boolean isErrorAny() {
	MediaEntry cur = head;
	while (cur != null) {
	    if ((cur.getStatus(false, true) & ERRORED) != 0) {
		return true;
	    }
	    cur = cur.next;
	}
	return false;
    }

    /**
     * Returns a list of all media that have encountered an error.
     * @return       an array of media objects tracked by this 
     *                        media tracker that have encountered 
     *                        an error, or <code>null</code> if 
     *                        there are none with errors.
     * @see          java.awt.MediaTracker#isErrorAny
     * @see          java.awt.MediaTracker#getErrorsID
     */
    public synchronized Object[] getErrorsAny() {
	MediaEntry cur = head;
	int numerrors = 0;
	while (cur != null) {
	    if ((cur.getStatus(false, true) & ERRORED) != 0) {
		numerrors++;
	    }
	    cur = cur.next;
	}
	if (numerrors == 0) {
	    return null;
	}
	Object errors[] = new Object[numerrors];
	cur = head;
	numerrors = 0;
	while (cur != null) {
	    if ((cur.getStatus(false, false) & ERRORED) != 0) {
		errors[numerrors++] = cur.getMedia();
	    }
	    cur = cur.next;
	}
	return errors;
    }

    /**
     * Starts loading all images tracked by this media tracker. This 
     * method waits until all the images being tracked have finished 
     * loading. 
     * <p>
     * If there is an error while loading or scaling an image, then that 
     * image is considered to have finished loading. Use the 
     * <code>isErrorAny</code> or <code>isErrorID</code> methods to 
     * check for errors. 
     * @see         java.awt.MediaTracker#waitForID(int)
     * @see         java.awt.MediaTracker#waitForAll(long)
     * @see         java.awt.MediaTracker#isErrorAny
     * @see         java.awt.MediaTracker#isErrorID
     * @exception   InterruptedException  if another thread has 
     *                                     interrupted this thread.
     */
    public void waitForAll() throws InterruptedException {
	waitForAll(0);
    }

    /**
     * Starts loading all images tracked by this media tracker. This 
     * method waits until all the images being tracked have finished 
     * loading, or until the length of time specified in milliseconds  
     * by the <code>ms</code> argument has passed. 
     * <p>
     * If there is an error while loading or scaling an image, then  
     * that image is considered to have finished loading. Use the 
     * <code>isErrorAny</code> or <code>isErrorID</code> methods to 
     * check for errors. 
     * @param       ms       the number of milliseconds to wait 
     *                       for the loading to complete.
     * @return      <code>true</code> if all images were successfully 
     *                       loaded; <code>false</code> otherwise.
     * @see         java.awt.MediaTracker#waitForID(int)
     * @see         java.awt.MediaTracker#waitForAll(long)
     * @see         java.awt.MediaTracker#isErrorAny
     * @see         java.awt.MediaTracker#isErrorID
     * @exception   InterruptedException  if another thread has 
     *                                     interrupted this thread.
     */
    public synchronized boolean waitForAll(long ms)
	throws InterruptedException
    {
	long end = System.currentTimeMillis() + ms;
	boolean first = true;
	while (true) {
	    int status = statusAll(first, first);
	    if ((status & LOADING) == 0) {
		return (status == COMPLETE);
	    }
	    first = false;
	    long timeout;
	    if (ms == 0) {
		timeout = 0;
	    } else {
		timeout = end - System.currentTimeMillis();
		if (timeout <= 0) {
		    return false;
		}
	    }
	    wait(timeout);
	}
    }

    /**
     * Calculates and returns the bitwise inclusive <b>OR</b> of the 
     * status of all media that are tracked by this media tracker. 
     * <p>
     * Possible flags defined by the 
     * <code>MediaTracker</code> class are <code>LOADING</code>, 
     * <code>ABORTED</code>, <code>ERRORED</code>, and 
     * <code>COMPLETE</code>. An image that hasn't started 
     * loading has zero as its status. 
     * <p>
     * If the value of <code>load</code> is <code>true</code>, then
     * this method starts loading any images that are not yet being loaded. 
     * @param        load   if <code>true</code>, start loading 
     *                            any images that are not yet being loaded.
     * @return       the bitwise inclusive <b>OR</b> of the status of 
     *                            all of the media being tracked.
     * @see          java.awt.MediaTracker#statusID(int, boolean)
     * @see          java.awt.MediaTracker#LOADING
     * @see          java.awt.MediaTracker#ABORTED
     * @see          java.awt.MediaTracker#ERRORED
     * @see          java.awt.MediaTracker#COMPLETE
     */
    public int statusAll(boolean load) {
	return statusAll(load, true);
    }

    private synchronized int statusAll(boolean load, boolean verify) {
	MediaEntry cur = head;
	int status = 0;
	while (cur != null) {
	    status = status | cur.getStatus(load, verify);
	    cur = cur.next;
	}
	return status;
    }

    /**
     * Checks to see if all images tracked by this media tracker that 
     * are tagged with the specified identifier have finished loading. 
     * <p>
     * This method does not start loading the images if they are not 
     * already loading. 
     * <p>
     * If there is an error while loading or scaling an image, then that 
     * image is considered to have finished loading. Use the 
     * <code>isErrorAny</code> or <code>isErrorID</code> methods to 
     * check for errors. 
     * @param       id   the identifier of the images to check.
     * @return      <code>true</code> if all images have finished loading, 
     *                       have been aborted, or have encountered 
     *                       an error; <code>false</code> otherwise.
     * @see         java.awt.MediaTracker#checkID(int, boolean)
     * @see         java.awt.MediaTracker#checkAll()
     * @see         java.awt.MediaTracker#isErrorAny()
     * @see         java.awt.MediaTracker#isErrorID(int)
     */
    public boolean checkID(int id) {
	return checkID(id, false, true);
    }

    /**
     * Checks to see if all images tracked by this media tracker that 
     * are tagged with the specified identifier have finished loading. 
     * <p>
     * If the value of the <code>load</code> flag is <code>true</code>, 
     * then this method starts loading any images that are not yet 
     * being loaded. 
     * <p>
     * If there is an error while loading or scaling an image, then that 
     * image is considered to have finished loading. Use the 
     * <code>isErrorAny</code> or <code>isErrorID</code> methods to 
     * check for errors. 
     * @param       id       the identifier of the images to check.
     * @param       load     if <code>true</code>, start loading any 
     *                       images that are not yet being loaded.
     * @return      <code>true</code> if all images have finished loading, 
     *                       have been aborted, or have encountered 
     *                       an error; <code>false</code> otherwise.
     * @see         java.awt.MediaTracker#checkID(int, boolean)
     * @see         java.awt.MediaTracker#checkAll()
     * @see         java.awt.MediaTracker#isErrorAny()
     * @see         java.awt.MediaTracker#isErrorID(int)
     */
    public boolean checkID(int id, boolean load) {
	return checkID(id, load, true);
    }

    private synchronized boolean checkID(int id, boolean load, boolean verify)
    {
	MediaEntry cur = head;
	boolean done = true;
	while (cur != null) {
	    if (cur.getID() == id
		&& (cur.getStatus(load, verify) & DONE) == 0)
	    {
		done = false;
	    }
	    cur = cur.next;
	}
	return done;
    }

    /**
     * Checks the error status of all of the images tracked by this 
     * media tracker with the specified identifier. 
     * @param        id   the identifier of the images to check.
     * @return       <code>true</code> if any of the images with the 
     *                          specified identifier had an error during 
     *                          loading; <code>false</code> otherwise.
     * @see          java.awt.MediaTracker#isErrorAny
     * @see          java.awt.MediaTracker#getErrorsID
     */
    public synchronized boolean isErrorID(int id) {
	MediaEntry cur = head;
	while (cur != null) {
	    if (cur.getID() == id
		&& (cur.getStatus(false, true) & ERRORED) != 0)
	    {
		return true;
	    }
	    cur = cur.next;
	}
	return false;
    }

    /**
     * Returns a list of media with the specified ID that 
     * have encountered an error.
     * @param       id   the identifier of the images to check.
     * @return      an array of media objects tracked by this media 
     *                       tracker with the specified identifier 
     *                       that have encountered an error, or 
     *                       <code>null</code> if there are none with errors.
     * @see         java.awt.MediaTracker#isErrorID
     * @see         java.awt.MediaTracker#isErrorAny
     * @see         java.awt.MediaTracker#getErrorsAny
     */
    public synchronized Object[] getErrorsID(int id) {
	MediaEntry cur = head;
	int numerrors = 0;
	while (cur != null) {
	    if (cur.getID() == id
		&& (cur.getStatus(false, true) & ERRORED) != 0)
	    {
		numerrors++;
	    }
	    cur = cur.next;
	}
	if (numerrors == 0) {
	    return null;
	}
	Object errors[] = new Object[numerrors];
	cur = head;
	numerrors = 0;
	while (cur != null) {
	    if (cur.getID() == id
		&& (cur.getStatus(false, false) & ERRORED) != 0)
	    {
		errors[numerrors++] = cur.getMedia();
	    }
	    cur = cur.next;
	}
	return errors;
    }

    /**
     * Starts loading all images tracked by this media tracker with the 
     * specified identifier. This method waits until all the images with 
     * the specified identifier have finished loading. 
     * <p>
     * If there is an error while loading or scaling an image, then that 
     * image is considered to have finished loading. Use the 
     * <code>isErrorAny</code> and <code>isErrorID</code> methods to 
     * check for errors. 
     * @param         id   the identifier of the images to check.
     * @see           java.awt.MediaTracker#waitForAll
     * @see           java.awt.MediaTracker#isErrorAny()
     * @see           java.awt.MediaTracker#isErrorID(int)
     * @exception     InterruptedException  if another thread has 
     *                          interrupted this thread.
     */
    public void waitForID(int id) throws InterruptedException {
	waitForID(id, 0);
    }

    /**
     * Starts loading all images tracked by this media tracker with the 
     * specified identifier. This method waits until all the images with 
     * the specified identifier have finished loading, or until the 
     * length of time specified in milliseconds by the <code>ms</code> 
     * argument has passed. 
     * <p>
     * If there is an error while loading or scaling an image, then that 
     * image is considered to have finished loading. Use the 
     * <code>statusID</code>, <code>isErrorID</code>, and
     * <code>isErrorAny</code> methods to check for errors. 
     * @param         id   the identifier of the images to check.
     * @param         ms   the length of time, in milliseconds, to wait 
     *                           for the loading to complete.
     * @see           java.awt.MediaTracker#waitForAll
     * @see           java.awt.MediaTracker#waitForID(int)
     * @see           java.awt.MediaTracker#statusID
     * @see           java.awt.MediaTracker#isErrorAny()
     * @see           java.awt.MediaTracker#isErrorID(int)
     * @exception     InterruptedException  if another thread has 
     *                          interrupted this thread.
     */
    public synchronized boolean waitForID(int id, long ms)
	throws InterruptedException
    {
	long end = System.currentTimeMillis() + ms;
	boolean first = true;
	while (true) {
	    int status = statusID(id, first, first);
	    if ((status & LOADING) == 0) {
		return (status == COMPLETE);
	    }
	    first = false;
	    long timeout;
	    if (ms == 0) {
		timeout = 0;
	    } else {
		timeout = end - System.currentTimeMillis();
		if (timeout <= 0) {
		    return false;
		}
	    }
	    wait(timeout);
	}
    }

    /**
     * Calculates and returns the bitwise inclusive <b>OR</b> of the 
     * status of all media with the specified identifier that are 
     * tracked by this media tracker. 
     * <p>
     * Possible flags defined by the 
     * <code>MediaTracker</code> class are <code>LOADING</code>, 
     * <code>ABORTED</code>, <code>ERRORED</code>, and 
     * <code>COMPLETE</code>. An image that hasn't started 
     * loading has zero as its status. 
     * <p>
     * If the value of <code>load</code> is <code>true</code>, then
     * this method starts loading any images that are not yet being loaded. 
     * @param        id   the identifier of the images to check.
     * @param        load   if <code>true</code>, start loading 
     *                            any images that are not yet being loaded.
     * @return       the bitwise inclusive <b>OR</b> of the status of 
     *                            all of the media with the specified
     *                            identifier that are being tracked.
     * @see          java.awt.MediaTracker#statusAll(boolean)
     * @see          java.awt.MediaTracker#LOADING
     * @see          java.awt.MediaTracker#ABORTED
     * @see          java.awt.MediaTracker#ERRORED
     * @see          java.awt.MediaTracker#COMPLETE
     */
    public int statusID(int id, boolean load) {
	return statusID(id, load, true);
    }

    private synchronized int statusID(int id, boolean load, boolean verify) {
	MediaEntry cur = head;
	int status = 0;
	while (cur != null) {
	    if (cur.getID() == id) {
		status = status | cur.getStatus(load, verify);
	    }
	    cur = cur.next;
	}
	return status;
    }

    /**
     * Remove the specified image from this media tracker.
     * All instances of the specified image are removed, 
     * regardless of scale or ID.
     * @param   image     the image to be removed
     * @see     java.awt.MediaTracker#removeImage(java.awt.Image, int)
     * @see     java.awt.MediaTracker#removeImage(java.awt.Image, int, int, int)
     * @since   JDK1.1
     */
    public synchronized void removeImage(Image image) {
	MediaEntry cur = head;
	MediaEntry prev = null;
	while (cur != null) {
	    MediaEntry next = cur.next;
	    if (cur.getMedia() == image) {
		if (prev == null) {
		    head = next;
		} else {
		    prev.next = next;
		}
		cur.cancel();
	    } else {
		prev = cur;
	    }
	    cur = next;
	}
	notifyAll();	// Notify in case remaining images are "done".
    }

    /**
     * Remove the specified image from the specified tracking 
     * ID of this media tracker.
     * All instances of <code>Image</code> being tracked 
     * under the specified ID are removed regardless of scale.
     * @param      image the image to be removed.
     * @param      id the tracking ID frrom which to remove the image.
     * @see        java.awt.MediaTracker#removeImage(java.awt.Image)
     * @see        java.awt.MediaTracker#removeImage(java.awt.Image, int, int, int)
     * @since      JDK1.1
     */
    public synchronized void removeImage(Image image, int id) {
	MediaEntry cur = head;
	MediaEntry prev = null;
	while (cur != null) {
	    MediaEntry next = cur.next;
	    if (cur.getID() == id && cur.getMedia() == image) {
		if (prev == null) {
		    head = next;
		} else {
		    prev.next = next;
		}
		cur.cancel();
	    } else {
		prev = cur;
	    }
	    cur = next;
	}
	notifyAll();	// Notify in case remaining images are "done".
    }

    /**
     * Remove the specified image with the specified 
     * width, height, and ID from this media tracker.
     * Only the specified instance (with any duplicates) is removed.
     * @param   image the image to be removed
     * @param   id the tracking ID from which to remove the image.
     * @param   width the width to remove (-1 for unscaled).
     * @param   height the height to remove (-1 for unscaled).
     * @see     java.awt.MediaTracker#removeImage(java.awt.Image)
     * @see     java.awt.MediaTracker#removeImage(java.awt.Image, int)
     * @since   JDK1.1
     */
    public synchronized void removeImage(Image image, int id,
					 int width, int height) {
	MediaEntry cur = head;
	MediaEntry prev = null;
	while (cur != null) {
	    MediaEntry next = cur.next;
	    if (cur.getID() == id && cur instanceof ImageMediaEntry
		&& ((ImageMediaEntry) cur).matches(image, width, height))
	    {
		if (prev == null) {
		    head = next;
		} else {
		    prev.next = next;
		}
		cur.cancel();
	    } else {
		prev = cur;
	    }
	    cur = next;
	}
	notifyAll();	// Notify in case remaining images are "done".
    }

    synchronized void setDone() {
	notifyAll();
    }
}

abstract class MediaEntry {
    MediaTracker tracker;
    int ID;
    MediaEntry next;

    int status;
    boolean cancelled;

    /*
     * JDK 1.1 serialVersionUID 
     */
    private static final long serialVersionUID = -2924957284304726459L;

    MediaEntry(MediaTracker mt, int id) {
	tracker = mt;
	ID = id;
    }

    abstract Object getMedia();

    static MediaEntry insert(MediaEntry head, MediaEntry me) {
	MediaEntry cur = head;
	MediaEntry prev = null;
	while (cur != null) {
	    if (cur.ID > me.ID) {
		break;
	    }
	    prev = cur;
	    cur = cur.next;
	}
	me.next = cur;
	if (prev == null) {
	    head = me;
	} else {
	    prev.next = me;
	}
	return head;
    }

    int getID() {
	return ID;
    }

    abstract void startLoad();

    void cancel() {
	cancelled = true;
    }

    static final int LOADING = MediaTracker.LOADING;
    static final int ABORTED = MediaTracker.ABORTED;
    static final int ERRORED = MediaTracker.ERRORED;
    static final int COMPLETE = MediaTracker.COMPLETE;

    static final int LOADSTARTED = (LOADING | ERRORED | COMPLETE);
    static final int DONE = (ABORTED | ERRORED | COMPLETE);

    synchronized int getStatus(boolean doLoad, boolean doVerify) {
	if (doLoad && ((status & LOADSTARTED) == 0)) {
	    status = (status & ~ABORTED) | LOADING;
	    startLoad();
	}
	return status;
    }

    void setStatus(int flag) {
	synchronized (this) {
	    status = flag;
	}
	tracker.setDone();
    }
}

class ImageMediaEntry extends MediaEntry implements ImageObserver, 
java.io.Serializable {
    Image image;
    int width;
    int height;

    ImageMediaEntry(MediaTracker mt, Image img, int c, int w, int h) {
	super(mt, c);
	image = img;
	width = w;
	height = h;
    }

    boolean matches(Image img, int w, int h) {
	return (image == img && width == w && height == h);
    }

    Object getMedia() {
	return image;
    }

    int getStatus(boolean doLoad, boolean doVerify) {
	if (doVerify) {
	    int flags = tracker.target.checkImage(image, width, height, null);
	    int s = parseflags(flags);
	    if (s == 0) {
		if ((status & (ERRORED | COMPLETE)) != 0) {
		    setStatus(ABORTED);
		}
	    } else if (s != status) {
		setStatus(s);
	    }
	}
	return super.getStatus(doLoad, doVerify);
    }

    void startLoad() {
	if (tracker.target.prepareImage(image, width, height, this)) {
	    setStatus(COMPLETE);
	}
    }

    int parseflags(int infoflags) {
	if ((infoflags & ERROR) != 0) {
	    return ERRORED;
	} else if ((infoflags & ABORT) != 0) {
	    return ABORTED;
	} else if ((infoflags & (ALLBITS | FRAMEBITS)) != 0) {
	    return COMPLETE;
	}
	return 0;
    }

    public boolean imageUpdate(Image img, int infoflags,
			       int x, int y, int w, int h) {
	if (cancelled) {
	    return false;
	}
	int s = parseflags(infoflags);
	if (s != 0 && s != status) {
	    setStatus(s);
	}
	return ((status & LOADING) != 0);
    }
}