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MediaTracker.javaAPI DocJava SE 5 API30121Fri Aug 26 14:56:46 BST 2005java.awt

MediaTracker

public class MediaTracker extends Object implements 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 {@link 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);
}
}
}

version
1.42, 12/19/03
author
Jim Graham
since
JDK1.0

Fields 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.
private static final long
serialVersionUID
public static final int
LOADING
Flag indicating that media is currently being loaded.
public static final int
ABORTED
Flag indicating that the downloading of media was aborted.
public static final int
ERRORED
Flag indicating that the downloading of media encountered an error.
public static final int
COMPLETE
Flag indicating that the downloading of media was completed successfully.
static final int
DONE
Constructors Summary
public MediaTracker(Component comp)
Creates a media tracker to track images for a given component.

param
comp the component on which the images will eventually be drawn


                                                         
       
	target = comp;
    
Methods Summary
public voidaddImage(java.awt.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.

param
image the image to be tracked
param
id an identifier used to track this image

	addImage(image, id, -1, -1);
    
public synchronized voidaddImage(java.awt.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.

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

	head = MediaEntry.insert(head,
				 new ImageMediaEntry(this, image, id, w, h));
    
public booleancheckAll()
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.

return
true if all images have finished loading, have been aborted, or have encountered an error; false otherwise
see
java.awt.MediaTracker#checkAll(boolean)
see
java.awt.MediaTracker#checkID
see
java.awt.MediaTracker#isErrorAny
see
java.awt.MediaTracker#isErrorID


                                                                                                                                                                                           
       
	return checkAll(false, true);
    
public booleancheckAll(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.

param
load if true, start loading any images that are not yet being loaded
return
true if all images have finished loading, have been aborted, or have encountered an error; false otherwise
see
java.awt.MediaTracker#checkID
see
java.awt.MediaTracker#checkAll()
see
java.awt.MediaTracker#isErrorAny()
see
java.awt.MediaTracker#isErrorID(int)

	return checkAll(load, true);
    
private synchronized booleancheckAll(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;
    
public booleancheckID(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.

param
id the identifier of the images to check
return
true if all images have finished loading, have been aborted, or have encountered an error; 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)

	return checkID(id, false, true);
    
public booleancheckID(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.

param
id the identifier of the images to check
param
load if true, start loading any images that are not yet being loaded
return
true if all images have finished loading, have been aborted, or have encountered an error; 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)

	return checkID(id, load, true);
    
private synchronized booleancheckID(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;
    
public synchronized java.lang.Object[]getErrorsAny()
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 null if there are none with errors
see
java.awt.MediaTracker#isErrorAny
see
java.awt.MediaTracker#getErrorsID

	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;
    
public synchronized java.lang.Object[]getErrorsID(int id)
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 null if there are none with errors
see
java.awt.MediaTracker#isErrorID
see
java.awt.MediaTracker#isErrorAny
see
java.awt.MediaTracker#getErrorsAny

	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;
    
public synchronized booleanisErrorAny()
Checks the error status of all of the images.

return
true if any of the images tracked by this media tracker had an error during loading; false otherwise
see
java.awt.MediaTracker#isErrorID
see
java.awt.MediaTracker#getErrorsAny

	MediaEntry cur = head;
	while (cur != null) {
	    if ((cur.getStatus(false, true) & ERRORED) != 0) {
		return true;
	    }
	    cur = cur.next;
	}
	return false;
    
public synchronized booleanisErrorID(int id)
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
true if any of the images with the specified identifier had an error during loading; false otherwise
see
java.awt.MediaTracker#isErrorAny
see
java.awt.MediaTracker#getErrorsID

	MediaEntry cur = head;
	while (cur != null) {
	    if (cur.getID() == id
		&& (cur.getStatus(false, true) & ERRORED) != 0)
	    {
		return true;
	    }
	    cur = cur.next;
	}
	return false;
    
public synchronized voidremoveImage(java.awt.Image image)
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

	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".
    
public synchronized voidremoveImage(java.awt.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.

param
image the image to be removed
param
id the tracking ID frrom 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

	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".
    
public synchronized voidremoveImage(java.awt.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.

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

	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 voidsetDone()

	notifyAll();
    
public intstatusAll(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.

param
load if true, start loading any images that are not yet being loaded
return
the bitwise inclusive 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

	return statusAll(load, true);
    
private synchronized intstatusAll(boolean load, boolean verify)

	MediaEntry cur = head;
	int status = 0;
	while (cur != null) {
	    status = status | cur.getStatus(load, verify);
	    cur = cur.next;
	}
	return status;
    
public intstatusID(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.

param
id the identifier of the images to check
param
load if true, start loading any images that are not yet being loaded
return
the bitwise inclusive 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

	return statusID(id, load, true);
    
private synchronized intstatusID(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;
    
public synchronized booleanwaitForAll(long ms)
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.

param
ms the number of milliseconds to wait for the loading to complete
return
true if all images were successfully loaded; 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 another thread has interrupted this thread.

	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);
	}
    
public voidwaitForAll()
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.

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 another thread has interrupted this thread

	waitForAll(0);
    
public voidwaitForID(int id)
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.

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 another thread has interrupted this thread.

	waitForID(id, 0);
    
public synchronized booleanwaitForID(int id, long ms)
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.

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 another thread has interrupted this thread.

	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);
	}