Class java.awt.MediaTracker 
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Class java.awt.MediaTracker 

java.lang.Object
|
   +----java.awt.MediaTracker
public class MediaTracker
extends Object
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);
	    }
	}
}

Variable Index

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

Constructor Index

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

Method Index

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

Variables

o LOADING 
public final static int LOADING
Flag indicating some media is currently being loaded.
See Also:
statusAll, statusID
o ABORTED 
public final static int ABORTED
Flag indicating the download of some media was aborted.
See Also:
statusAll, statusID
o ERRORED 
public final static int ERRORED
Flag indicating the download of some media encountered an error.
See Also:
statusAll, statusID
o COMPLETE 
public final static int COMPLETE
Flag indicating the download of media completed successfully.
See Also:
statusAll, statusID

Constructors

o 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

Methods

o 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
o 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
o 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
o 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
o 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
o 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
o 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
o 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
o statusAll 
public 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
o 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
o 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
o 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
o 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
o 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
o 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
o statusID 
public 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 
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