public class MediaTracker extends Object implements Serializable
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); } } }
| Modifier and Type | Field and Description | 
|---|---|
| static int | ABORTEDFlag indicating that the downloading of media was aborted. | 
| static int | COMPLETEFlag indicating that the downloading of media was completed
 successfully. | 
| static int | ERROREDFlag indicating that the downloading of media encountered
 an error. | 
| static int | LOADINGFlag indicating that media is currently being loaded. | 
| Constructor and Description | 
|---|
| MediaTracker(Component comp)Creates a media tracker to track images for a given component. | 
| Modifier and Type | Method and Description | 
|---|---|
| void | addImage(Image image,
        int id)Adds an image to the list of images being tracked by this media
 tracker. | 
| 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. | 
| boolean | checkAll()Checks to see if all images being tracked by this media tracker
 have finished loading. | 
| boolean | checkAll(boolean load)Checks to see if all images being tracked by this media tracker
 have finished loading. | 
| 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. | 
| 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. | 
| Object[] | getErrorsAny()Returns a list of all media that have encountered an error. | 
| Object[] | getErrorsID(int id)Returns a list of media with the specified ID that
 have encountered an error. | 
| boolean | isErrorAny()Checks the error status of all of the images. | 
| boolean | isErrorID(int id)Checks the error status of all of the images tracked by this
 media tracker with the specified identifier. | 
| void | removeImage(Image image)Removes the specified image from this media tracker. | 
| void | removeImage(Image image,
           int id)Removes the specified image from the specified tracking
 ID of this media tracker. | 
| 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. | 
| int | statusAll(boolean load)Calculates and returns the bitwise inclusive OR of the
 status of all media that are tracked by this media tracker. | 
| 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. | 
| void | waitForAll()Starts loading all images tracked by this media tracker. | 
| boolean | waitForAll(long ms)Starts loading all images tracked by this media tracker. | 
| void | waitForID(int id)Starts loading all images tracked by this media tracker with the
 specified identifier. | 
| boolean | waitForID(int id,
         long ms)Starts loading all images tracked by this media tracker with the
 specified identifier. | 
public static final int LOADING
public static final int ABORTED
public static final int ERRORED
public static final int COMPLETE
public MediaTracker(Component comp)
comp - the component on which the images
                     will eventually be drawnpublic void addImage(Image image, int id)
image - the image to be trackedid - an identifier used to track this imagepublic void addImage(Image image, int id, int w, int h)
image - the image to be trackedid - an identifier that can be used to track this imagew - the width at which the image is renderedh - the height at which the image is renderedpublic boolean checkAll()
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.
true if all images have finished loading,
                       have been aborted, or have encountered
                       an error; false otherwisecheckAll(boolean), 
checkID(int), 
isErrorAny(), 
isErrorID(int)public boolean checkAll(boolean load)
 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.
load - if true, start loading any
                       images that are not yet being loadedtrue if all images have finished loading,
                       have been aborted, or have encountered
                       an error; false otherwisecheckID(int), 
checkAll(), 
isErrorAny(), 
isErrorID(int)public boolean isErrorAny()
true if any of the images tracked
                  by this media tracker had an error during
                  loading; false otherwiseisErrorID(int), 
getErrorsAny()public Object[] getErrorsAny()
null if
                        there are none with errorsisErrorAny(), 
getErrorsID(int)public void waitForAll()
                throws InterruptedException
 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.
InterruptedException - if any thread has
                                     interrupted this threadwaitForID(int), 
waitForAll(long), 
isErrorAny(), 
isErrorID(int)public boolean waitForAll(long ms)
                   throws InterruptedException
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.
ms - the number of milliseconds to wait
                       for the loading to completetrue if all images were successfully
                       loaded; false otherwiseInterruptedException - if any thread has
                                     interrupted this thread.waitForID(int), 
waitForAll(long), 
isErrorAny(), 
isErrorID(int)public int statusAll(boolean load)
 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.
load - if true, start loading
                            any images that are not yet being loadedstatusID(int, boolean), 
LOADING, 
ABORTED, 
ERRORED, 
COMPLETEpublic boolean checkID(int id)
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.
id - the identifier of the images to checktrue if all images have finished loading,
                       have been aborted, or have encountered
                       an error; false otherwisecheckID(int, boolean), 
checkAll(), 
isErrorAny(), 
isErrorID(int)public boolean checkID(int id,
                       boolean load)
 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.
id - the identifier of the images to checkload - if true, start loading any
                       images that are not yet being loadedtrue if all images have finished loading,
                       have been aborted, or have encountered
                       an error; false otherwisecheckID(int, boolean), 
checkAll(), 
isErrorAny(), 
isErrorID(int)public boolean isErrorID(int id)
id - the identifier of the images to checktrue if any of the images with the
                          specified identifier had an error during
                          loading; false otherwiseisErrorAny(), 
getErrorsID(int)public Object[] getErrorsID(int id)
id - the identifier of the images to checknull if there are none with errorsisErrorID(int), 
isErrorAny(), 
getErrorsAny()public void waitForID(int id)
               throws InterruptedException
 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.
id - the identifier of the images to checkInterruptedException - if any thread has
                          interrupted this thread.waitForAll(), 
isErrorAny(), 
isErrorID(int)public boolean waitForID(int id,
                         long ms)
                  throws InterruptedException
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.
id - the identifier of the images to checkms - the length of time, in milliseconds, to wait
                           for the loading to completeInterruptedException - if any thread has
                          interrupted this thread.waitForAll(), 
waitForID(int), 
statusID(int, boolean), 
isErrorAny(), 
isErrorID(int)public int statusID(int id,
                    boolean load)
 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.
id - the identifier of the images to checkload - if true, start loading
                            any images that are not yet being loadedstatusAll(boolean), 
LOADING, 
ABORTED, 
ERRORED, 
COMPLETEpublic void removeImage(Image image)
image - the image to be removedremoveImage(java.awt.Image, int), 
removeImage(java.awt.Image, int, int, int)public void removeImage(Image image, int id)
Image being tracked
 under the specified ID are removed regardless of scale.image - the image to be removedid - the tracking ID from which to remove the imageremoveImage(java.awt.Image), 
removeImage(java.awt.Image, int, int, int)public void removeImage(Image image, int id, int width, int height)
image - the image to be removedid - the tracking ID from which to remove the imagewidth - the width to remove (-1 for unscaled)height - the height to remove (-1 for unscaled)removeImage(java.awt.Image), 
removeImage(java.awt.Image, int) Submit a bug or feature 
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