    All Packages  Class Hierarchy  This Package  Previous  Next  Index

# Class java.awt.MediaTracker

    java.lang.Object
       |
       +----java.awt.MediaTracker

public class MediaTracker
extends Object
implements Serializable

A utility class to track the status of a number of media objects. Media objects could include images as well as audio clips, though currently only images are supported. To use it, simply create an instance and then call addImage() for each image to be tracked. Each image can be assigned a unique ID for indentification purposes. The IDs control the priority order in which the images are fetched as well as identifying unique subsets of the images that can be waited on independently. Here is an example:

     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.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 our 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);
    	    }
    	}
     }

##

ABORTED
  Flag indicating the download of some media was aborted.
COMPLETE
  Flag indicating the download of media completed successfully.
ERRORED
  Flag indicating the download of some media encountered an error.
LOADING
  Flag indicating some media is currently being loaded.

##

MediaTracker(Component)
  Creates a Media tracker to track images for a given Component.

##

addImage(Image, int)
  Adds an image to the list of images being tracked.
addImage(Image, int, int, int)
  Adds a scaled image to the list of images being tracked.
checkAll()
  Checks to see if all images have finished loading but does not start loading the images if they are not already loading.
checkAll(boolean)
  Checks to see if all images have finished loading.
checkID(int)
  Checks to see if all images tagged with the indicated ID have finished loading, but does not start loading the images if they are not already loading.
checkID(int, boolean)
  Checks to see if all images tagged with the indicated ID have finished loading.
getErrorsAny()
  Returns a list of all media that have encountered an error.
getErrorsID(int)
  Returns a list of media with the specified ID that have encountered an error.
isErrorAny()
  Checks the error status of all of the images.
isErrorID(int)
  Checks the error status of all of the images with the specified ID.
removeImage(Image)
  Remove the specified Image from this MediaTracker.
removeImage(Image, int)
  Remove the specified Image from the specified ID of this MediaTracker.
removeImage(Image, int, int, int)
  Remove the specified image with the specified size and ID from this MediaTracker.
statusAll(boolean)
  Returns the boolean OR of the status of all of the media being tracked.
statusID(int, boolean)
  Returns the boolean OR of the status of all of the media with a given ID.
waitForAll()
  Starts loading all images.
waitForAll(long)
  Starts loading all images.
waitForID(int)
  Starts loading all images with the specified ID and waits until they have finished loading or receive an error.
waitForID(int, long)
  Starts loading all images with the specified ID.

##

LOADING

      public final static int LOADING

  Flag indicating some media is currently being loaded.

  See Also:
    statusAll, statusID

ABORTED

      public final static int ABORTED

  Flag indicating the download of some media was aborted.

  See Also:
    statusAll, statusID

ERRORED

      public final static int ERRORED

  Flag indicating the download of some media encountered an error.

  See Also:
    statusAll, statusID

COMPLETE

      public final static int COMPLETE

  Flag indicating the download of media completed successfully.

  See Also:
    statusAll, statusID

##

MediaTracker

      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

##

addImage

      public void addImage(Image image,
                           int id)

  Adds an image to the list of images being tracked. The image will eventually be rendered at its default (unscaled) size.

  Parameters:
    image - the image to be tracked
    id - the identifier used to later track this image

addImage

      public synchronized void addImage(Image image,
                                        int id,
                                        int w,
                                        int h)

  Adds a scaled image to the list of images being tracked. The image will eventually be rendered at the indicated size.

  Parameters:
    image - the image to be tracked
    id - the identifier used to later track this image
    w - the width that the image will be rendered at
    h - the height that the image will be rendered at

checkAll

      public boolean checkAll()

  Checks to see if all images have finished loading but 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 "complete." Use isErrorAny() or isErrorID() to check for errors.

  Returns:
    true if all images have finished loading, were aborted or encountered an error
  See Also:
    checkAll, checkID, isErrorAny, isErrorID

checkAll

      public synchronized boolean checkAll(boolean load)

  Checks to see if all images have finished loading. If load is true, 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 "complete." Use isErrorAny() or isErrorID() to check for errors.

  Parameters:
    load - start loading the images if this parameter is true
  Returns:
    true if all images have finished loading, were aborted or encountered an error
  See Also:
    isErrorAny, isErrorID, checkID, checkAll

isErrorAny

      public synchronized boolean isErrorAny()

  Checks the error status of all of the images.

  Returns:
    true if any of the images had an error during loading
  See Also:
    isErrorID, getErrorsAny

getErrorsAny

      public synchronized Object[] getErrorsAny()

  Returns a list of all media that have encountered an error.

  Returns:
    an array of media objects or null if there are no errors
  See Also:
    isErrorAny, getErrorsID

waitForAll

      public void waitForAll() throws InterruptedException

  Starts loading all images. Waits until they have finished loading, are aborted, or it receives an error. If there is an error while loading or scaling an image then that image is considered "complete." Use isErrorAny() or statusAll() to check for errors.

  Throws: InterruptedException
    Another thread has interrupted this thread.
  See Also:
    waitForID, waitForAll, isErrorAny, isErrorID

waitForAll

      public synchronized boolean waitForAll(long ms) throws InterruptedException

  Starts loading all images. Waits until they have finished loading, are aborted, it receives an error, or until the specified timeout has elapsed. If there is an error while loading or scaling an image then that image is considered "complete." Use isErrorAny() or statusAll() to check for errors.

  Parameters:
    ms - the length of time to wait for the loading to complete
  Returns:
    true if all images were successfully loaded
  Throws: InterruptedException
    Another thread has interrupted this thread.
  See Also:
    waitForID, waitForAll, isErrorAny, isErrorID

statusAll

      public synchronized int statusAll(boolean load)

  Returns the boolean OR of the status of all of the media being tracked.

  Parameters:
    load - specifies whether to start the media loading
  See Also:
    statusID, LOADING, ABORTED, ERRORED, COMPLETE

checkID

      public boolean checkID(int id)

  Checks to see if all images tagged with the indicated ID have finished loading, but 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 "complete." Use isErrorAny() or isErrorID() to check for errors.

  Parameters:
    id - the identifier used to determine which images to check
  Returns:
    true if all tagged images have finished loading, were aborted, or an error occurred.
  See Also:
    checkID, checkAll, isErrorAny, isErrorID

checkID

      public synchronized boolean checkID(int id,
                                          boolean load)

  Checks to see if all images tagged with the indicated ID have finished loading. If load is true, starts loading any images with that ID that are not yet being loaded. If there is an error while loading or scaling an image then that image is considered "complete." Use isErrorAny() or isErrorID() to check for errors.

  Parameters:
    id - the identifier used to determine which images to check
    load - start loading the images if this parameter is true
  Returns:
    true if all tagged images have finished loading, were aborted, or an error occurred
  See Also:
    checkID, checkAll, isErrorAny, isErrorID

isErrorID

      public synchronized boolean isErrorID(int id)

  Checks the error status of all of the images with the specified ID.

  Parameters:
    id - the identifier used to determine which images to check
  Returns:
    true if any of the tagged images had an error during loading
  See Also:
    isErrorAny, getErrorsID

getErrorsID

      public synchronized Object[] getErrorsID(int id)

  Returns a list of media with the specified ID that have encountered an error.

  Parameters:
    id - the identifier used to determine which images to return
  Returns:
    an array of media objects or null if there are no errors
  See Also:
    isErrorID, getErrorsAny

waitForID

      public void waitForID(int id) throws InterruptedException

  Starts loading all images with the specified ID and waits until they have finished loading or receive an error. If there is an error while loading or scaling an image then that image is considered "complete." Use statusID() or isErrorID() to check for errors.

  Parameters:
    id - the identifier used to determine which images to wait for
  Throws: InterruptedException
    Another thread has interrupted this thread.
  See Also:
    waitForAll, waitForID, isErrorAny, isErrorID

waitForID

      public synchronized boolean waitForID(int id,
                                            long ms) throws InterruptedException

  Starts loading all images with the specified ID. Waits until they have finished loading, an error occurs, or the specified timeout has elapsed. If there is an error while loading or scaling an image then that image is considered "complete." Use statusID or isErrorID to check for errors.

  Parameters:
    id - the identifier used to determine which images to wait for
    ms - the length of time to wait for the loading to complete
  Throws: InterruptedException
    Another thread has interrupted this thread.
  See Also:
    waitForAll, waitForID, isErrorAny, isErrorID

statusID

      public synchronized int statusID(int id,
                                       boolean load)

  Returns the boolean OR of the status of all of the media with a given ID.

  Parameters:
    id - the identifier used to determine which images to check
    load - specifies whether to start the media loading
  See Also:
    statusAll, LOADING, ABORTED, ERRORED, COMPLETE

removeImage

      public synchronized void removeImage(Image image)

  Remove the specified Image from this MediaTracker. All instances of the image are removed regardless of scale or ID.

  Parameters:
    image - the image to be removed
  See Also:
    removeImage, removeImage

removeImage

      public synchronized void removeImage(Image image,
                                           int id)

  Remove the specified Image from the specified ID of this MediaTracker. All instances of the image being tracked under the given ID are removed regardless of scale.

  Parameters:
    image - the image to be removed
    id - the tracking ID to remove the image from
  See Also:
    removeImage, removeImage

removeImage

      public synchronized void removeImage(Image image,
                                           int id,
                                           int width,
                                           int height)

  Remove the specified image with the specified size and ID from this MediaTracker. Only the specific instance (with any duplicates) is removed.

  Parameters:
    image - the image to be removed
    id - the tracking ID to remove the image from
    width - the width to remove (-1 for unscaled)
    height - the height to remove (-1 for unscaled)
  See Also:
    removeImage, removeImage

    All Packages  Class Hierarchy  This Package  Previous  Next  Index