java.awt
Class 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);
	    }
	}
 }

 

Field Summary

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

Constructor Summary

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

Method Summary

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

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

LOADING

public static final int LOADING

Flag indicating some media is currently being loaded.

See Also:

statusAll(boolean), statusID(int, boolean), Constant Field Values

ABORTED

public static final int ABORTED

Flag indicating the download of some media was aborted.

See Also:

statusAll(boolean), statusID(int, boolean), Constant Field Values

ERRORED

public static final int ERRORED

Flag indicating the download of some media encountered an error.

See Also:

statusAll(boolean), statusID(int, boolean), Constant Field Values

COMPLETE

public static final int COMPLETE

Flag indicating the download of media completed successfully.

See Also:

statusAll(boolean), statusID(int, boolean), Constant Field Values

Constructor Detail

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

Method Detail

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 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(boolean), checkID(int), isErrorAny(), isErrorID(int)

checkAll

public 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(int), checkID(int, boolean), checkAll()

isErrorAny

public 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(int), getErrorsAny()

getErrorsAny

public 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(int)

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(int), waitForAll(long), isErrorAny(), isErrorID(int)

waitForAll

public 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(int), waitForAll(), isErrorAny(), isErrorID(int)

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(int, boolean), 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(int, boolean), checkAll(), isErrorAny(), isErrorID(int)

checkID

public 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(int), checkAll(), isErrorAny(), isErrorID(int)

isErrorID

public 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(int)

getErrorsID

public 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(int), 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(int, long), isErrorAny(), isErrorID(int)

waitForID

public 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(int), isErrorAny(), isErrorID(int)

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(boolean), LOADING, ABORTED, ERRORED, COMPLETE