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java.awt
public class: MediaTracker [javadoc | source]
java.lang.Object
   java.awt.MediaTracker

All Implemented Interfaces:
    java$io$Serializable

The 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.

To use a media tracker, create an instance of 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.

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. MediaTracker treats an animated image as completely loaded when the first frame is completely loaded. At that point, the MediaTracker signals any waiters that the image is completely loaded. If no ImageObservers are observing the image when the first frame has finished loading, the image might flush itself to conserve resources (see Image#flush() ).

Here is an example of using MediaTracker:


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);
         }
     }
}

Field Summary
 Component target    A given Component that will be tracked by a media tracker where the image will eventually be drawn. 
 MediaEntry head    The head of the list of Images that is being tracked by the MediaTracker. 
public static final  int LOADING    Flag indicating that media is currently being loaded.
    Also see:
    java.awt.MediaTracker#statusAll
    java.awt.MediaTracker#statusID
 
public static final  int ABORTED    Flag indicating that the downloading of media was aborted.
    Also see:
    java.awt.MediaTracker#statusAll
    java.awt.MediaTracker#statusID
 
public static final  int ERRORED    Flag indicating that the downloading of media encountered an error.
    Also see:
    java.awt.MediaTracker#statusAll
    java.awt.MediaTracker#statusID
 
public static final  int COMPLETE    Flag indicating that the downloading of media was completed successfully.
    Also see:
    java.awt.MediaTracker#statusAll
    java.awt.MediaTracker#statusID
 
static final  int DONE     
Constructor:
 public MediaTracker(Component comp) 
    Creates a media tracker to track images for a given component.
    Parameters:
    comp - the component on which the images will eventually be drawn
Method from java.awt.MediaTracker Summary:
addImage,   addImage,   checkAll,   checkAll,   checkID,   checkID,   getErrorsAny,   getErrorsID,   isErrorAny,   isErrorID,   removeImage,   removeImage,   removeImage,   setDone,   statusAll,   statusID,   waitForAll,   waitForAll,   waitForID,   waitForID
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from java.awt.MediaTracker Detail:
 public  void addImage(Image image,
    int id) 
    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.
 public synchronized  void addImage(Image image,
    int id,
    int w,
    int h) 
    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.
 public boolean checkAll() 
    Checks to see if all images being tracked by this media tracker have finished loading.

    This method does not start loading the images if they are not already loading.

    If there is an error while loading or scaling an image, then that image is considered to have finished loading. Use the isErrorAny or isErrorID methods to check for errors.

 public boolean checkAll(boolean load) 
    Checks to see if all images being tracked by this media tracker have finished loading.

    If the value of the load flag is true, then this method starts loading any images that are not yet being loaded.

    If there is an error while loading or scaling an image, that image is considered to have finished loading. Use the isErrorAny and isErrorID methods to check for errors.

 public boolean checkID(int id) 
    Checks to see if all images tracked by this media tracker that are tagged with the specified identifier have finished loading.

    This method does not start loading the images if they are not already loading.

    If there is an error while loading or scaling an image, then that image is considered to have finished loading. Use the isErrorAny or isErrorID methods to check for errors.

 public boolean checkID(int id,
    boolean load) 
    Checks to see if all images tracked by this media tracker that are tagged with the specified identifier have finished loading.

    If the value of the load flag is true, then this method starts loading any images that are not yet being loaded.

    If there is an error while loading or scaling an image, then that image is considered to have finished loading. Use the isErrorAny or isErrorID methods to check for errors.

 public synchronized Object[] getErrorsAny() 
    Returns a list of all media that have encountered an error.
 public synchronized Object[] getErrorsID(int id) 
    Returns a list of media with the specified ID that have encountered an error.
 public synchronized boolean isErrorAny() 
    Checks the error status of all of the images.
 public synchronized boolean isErrorID(int id) 
    Checks the error status of all of the images tracked by this media tracker with the specified identifier.
 public synchronized  void removeImage(Image image) 
    Removes the specified image from this media tracker. All instances of the specified image are removed, regardless of scale or ID.
 public synchronized  void removeImage(Image image,
    int id) 
    Removes the specified image from the specified tracking ID of this media tracker. All instances of Image being tracked under the specified ID are removed regardless of scale.
 public synchronized  void removeImage(Image image,
    int id,
    int width,
    int height) 
    Removes the specified image with the specified width, height, and ID from this media tracker. Only the specified instance (with any duplicates) is removed.
 synchronized  void setDone() 
 public int statusAll(boolean load) 
    Calculates and returns the bitwise inclusive OR of the status of all media that are tracked by this media tracker.

    Possible flags defined by the MediaTracker class are LOADING, ABORTED, ERRORED, and COMPLETE. An image that hasn't started loading has zero as its status.

    If the value of load is true, then this method starts loading any images that are not yet being loaded.

 public int statusID(int id,
    boolean load) 
    Calculates and returns the bitwise inclusive OR of the status of all media with the specified identifier that are tracked by this media tracker.

    Possible flags defined by the MediaTracker class are LOADING, ABORTED, ERRORED, and COMPLETE. An image that hasn't started loading has zero as its status.

    If the value of load is true, then this method starts loading any images that are not yet being loaded.

 public  void waitForAll() throws InterruptedException 
    Starts loading all images tracked by this media tracker. This method waits until all the images being tracked have finished loading.

    If there is an error while loading or scaling an image, then that image is considered to have finished loading. Use the isErrorAny or isErrorID methods to check for errors.

 public synchronized boolean waitForAll(long ms) throws InterruptedException 
    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 ms argument has passed.

    If there is an error while loading or scaling an image, then that image is considered to have finished loading. Use the isErrorAny or isErrorID methods to check for errors.

 public  void waitForID(int id) throws InterruptedException 
    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.

    If there is an error while loading or scaling an image, then that image is considered to have finished loading. Use the isErrorAny and isErrorID methods to check for errors.

 public synchronized boolean waitForID(int id,
    long ms) throws InterruptedException 
    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 ms argument has passed.

    If there is an error while loading or scaling an image, then that image is considered to have finished loading. Use the statusID, isErrorID, and isErrorAny methods to check for errors.