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Java example source code file (MediaTracker.java)

This example Java source code file (MediaTracker.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

aborted, awt, complete, done, errored, image, imagemediaentry, imageobserver, interruptedexception, loading, loadstarted, mediaentry, mediatracker, notify, object

The MediaTracker.java Java example source code

/*
 * Copyright (c) 1995, 2013, Oracle and/or its affiliates. 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.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 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 and call its addImage
 * 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 treats an animated image
 * as completely loaded
 * when the first frame is completely loaded.
 * At that point, the <code>MediaTracker
 * signals any waiters
 * that the image is completely loaded.
 * If no <code>ImageObservers 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:
 * <p>
 * <hr>
{@code
 * 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>

* * @author Jim Graham * @since JDK1.0 */ public class MediaTracker implements java.io.Serializable { /** * A given <code>Component 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 that is being * tracked by the <code>MediaTracker. * * @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 or isErrorID methods to * check for errors. * @return <code>true if all images have finished loading, * have been aborted, or have encountered * an error; <code>false 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 flag is true, * 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 and isErrorID methods to * check for errors. * @param load if <code>true, start loading any * images that are not yet being loaded * @return <code>true if all images have finished loading, * have been aborted, or have encountered * an error; <code>false 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 if any of the images tracked * by this media tracker had an error during * loading; <code>false 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 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 or isErrorID 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 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 or isErrorID methods to * check for errors. * @param ms the number of milliseconds to wait * for the loading to complete * @return <code>true if all images were successfully * loaded; <code>false 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 of the * status of all media that are tracked by this media tracker. * <p> * Possible flags defined by the * <code>MediaTracker class are LOADING, * <code>ABORTED, ERRORED, and * <code>COMPLETE. An image that hasn't started * loading has zero as its status. * <p> * If the value of <code>load is true, then * this method starts loading any images that are not yet being loaded. * * @param load if <code>true, start loading * any images that are not yet being loaded * @return the bitwise inclusive <b>OR 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 or isErrorID methods to * check for errors. * @param id the identifier of the images to check * @return <code>true if all images have finished loading, * have been aborted, or have encountered * an error; <code>false 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 flag is true, * 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 or isErrorID methods to * check for errors. * @param id the identifier of the images to check * @param load if <code>true, start loading any * images that are not yet being loaded * @return <code>true if all images have finished loading, * have been aborted, or have encountered * an error; <code>false 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 if any of the images with the * specified identifier had an error during * loading; <code>false 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 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 and isErrorID 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 * 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, isErrorID, and * <code>isErrorAny 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 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 class are LOADING, * <code>ABORTED, ERRORED, and * <code>COMPLETE. An image that hasn't started * loading has zero as its status. * <p> * If the value of <code>load is true, 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, start loading * any images that are not yet being loaded * @return the bitwise inclusive <b>OR 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 being tracked * under the specified ID are removed regardless of scale. * @param image the image to be removed * @param id the tracking ID from 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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