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Java Source Code / Java Documentation  » 6.0 JDK Core » AWT » java.awt 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


        /*
         * Copyright 1995-2007 Sun Microsystems, Inc.  All Rights Reserved.
         * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
         *
         * This code is free software; you can redistribute it and/or modify it
         * under the terms of the GNU General Public License version 2 only, as
         * published by the Free Software Foundation.  Sun designates this
         * particular file as subject to the "Classpath" exception as provided
         * by Sun in the LICENSE file that accompanied this code.
         *
         * This code is distributed in the hope that it will be useful, but WITHOUT
         * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
         * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
         * version 2 for more details (a copy is included in the LICENSE file that
         * accompanied this code).
         *
         * You should have received a copy of the GNU General Public License version
         * 2 along with this work; if not, write to the Free Software Foundation,
         * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
         *
         * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
         * CA 95054 USA or visit www.sun.com if you need additional information or
         * have any questions.
         */

        package java.awt;

        import java.awt.Component;
        import java.awt.Image;
        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>
         *
         * Tracking an animated image 
         * might not always be useful
         * due to the multi-part nature of animated image
         * loading and painting,
         * but it is supported.
         * <code>MediaTracker</code> treats an animated image
         * as completely loaded
         * when the first frame is completely loaded.
         * At that point, the <code>MediaTracker</code> 
         * signals any waiters 
         * that the image is completely loaded.
         * If no <code>ImageObserver</code>s are observing the image
         * when the first frame has finished loading,
         * the image might flush itself
         * to conserve resources
         * (see {@link Image#flush()}).
         *
         * <p>
         * Here is an example of using <code>MediaTracker</code>: 
         * <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>
         *
         * @version 	1.52, 06/05/07
         * @author 	Jim Graham
         * @since       JDK1.0
         */
        public class MediaTracker implements  java.io.Serializable {

            /**
             * A given <code>Component</code> that will be
             * tracked by a media tracker where the image will
             * eventually be drawn.
             *
             * @serial
             * @see #MediaTracker(Component)
             */
            Component target;
            /**
             * The head of the list of <code>Images</code> that is being
             * tracked by the <code>MediaTracker</code>.
             *
             * @serial
             * @see #addImage(Image, int)
             * @see #removeImage(Image)
             */
            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 that 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 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 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 any 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 any 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 any 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 any 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;
            }

            /**
             * Removes 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".
            }

            /**
             * Removes 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".
            }

            /**
             * Removes 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;

            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;

            /*
             * JDK 1.1 serialVersionUID 
             */
            private static final long serialVersionUID = 4739377000350280650L;

            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;
            }

            synchronized 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);
            }
        }
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