java.awt
Class MediaTracker

java.lang.Object
  java.awt.MediaTracker

All Implemented Interfaces:

Serializable

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 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);
            }
        }
 }
 

Since:

JDK1.0

See Also:

Serialized Form

Field Summary

static int	ABORTED Flag indicating that the downloading of media was aborted.
static int	COMPLETE Flag indicating that the downloading of media was completed successfully.
static int	ERRORED Flag indicating that the downloading of media encountered an error.
static int	LOADING Flag indicating that 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 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.

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 that media is currently being loaded.

See Also:

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

ABORTED

public static final int ABORTED

Flag indicating that the downloading of media was aborted.

See Also:

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

ERRORED

public static final int ERRORED

Flag indicating that the downloading of media encountered an error.

See Also:

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

COMPLETE

public static final int COMPLETE

Flag indicating that the downloading of media was 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 by this media tracker. The image will eventually be rendered at its default (unscaled) size.

Parameters:

image - the image to be tracked

id - an identifier used to 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 by this media tracker. The image will eventually be rendered at the indicated width and height.

Parameters:

image - the image to be tracked

id - an identifier that can be used to track this image

w - the width at which the image is rendered

h - the height at which the image is rendered

checkAll

public boolean checkAll()

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.

Returns:

true if all images have finished loading, have been aborted, or have encountered an error; false otherwise

See Also:

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

checkAll

public boolean checkAll(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.

Parameters:

load - if true, start loading any images that are not yet being loaded

Returns:

true if all images have finished loading, have been aborted, or have encountered an error; false otherwise

See Also:

checkID(int), checkAll(), isErrorAny(), isErrorID(int)

isErrorAny

public boolean isErrorAny()

Checks the error status of all of the images.

Returns:

true if any of the images tracked by this media tracker had an error during loading; false otherwise

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 tracked by this media tracker that have encountered an error, or null if there are none with errors

See Also:

isErrorAny(), getErrorsID(int)

waitForAll

public void waitForAll()
                throws InterruptedException

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.

Throws:

InterruptedException - if any 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 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.

Parameters:

ms - the number of milliseconds to wait for the loading to complete

Returns:

true if all images were successfully loaded; false otherwise

Throws:

InterruptedException - if any thread has interrupted this thread.

See Also:

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

statusAll

public int statusAll(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.

Parameters:

load - if true, start loading any images that are not yet being loaded

Returns:

the bitwise inclusive OR of the status of all of the media being tracked

See Also:

statusID(int, boolean), LOADING, ABORTED, ERRORED, COMPLETE

checkID

public 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.

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.

Parameters:

id - the identifier of the images to check

Returns:

true if all images have finished loading, have been aborted, or have encountered an error; false otherwise

See Also:

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

checkID

public 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.

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.

Parameters:

id - the identifier of the images to check

load - if true, start loading any images that are not yet being loaded

Returns:

true if all images have finished loading, have been aborted, or have encountered an error; false otherwise

See Also:

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

isErrorID

public boolean isErrorID(int id)

Checks the error status of all of the images tracked by this media tracker with the specified identifier.

Parameters:

id - the identifier of the images to check

Returns:

true if any of the images with the specified identifier had an error during loading; false otherwise

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 of the images to check

Returns:

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 Also:

isErrorID(int), isErrorAny(), getErrorsAny()

waitForID

public void waitForID(int id)
               throws InterruptedException

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.

Parameters:

id - the identifier of the images to check

Throws:

InterruptedException - if any thread has interrupted this thread.

See Also:

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

waitForID

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

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.

Parameters:

id - the identifier of the images to check

ms - the length of time, in milliseconds, to wait for the loading to complete

Throws:

InterruptedException - if any thread has interrupted this thread.

See Also:

waitForAll(), waitForID(int), statusID(int, boolean), isErrorAny(), isErrorID(int)

statusID

public 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.

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.

Parameters:

id - the identifier of the images to check

load - if true, start loading any images that are not yet being loaded

Returns:

the bitwise inclusive OR of the status of all of the media with the specified identifier that are being tracked

See Also:

statusAll(boolean), LOADING, ABORTED, ERRORED, COMPLETE

removeImage

public void removeImage(Image image)

Removes the specified image from this media tracker. All instances of the specified image are removed, regardless of scale or ID.

Parameters:

image - the image to be removed

Since:

JDK1.1

See Also:

removeImage(java.awt.Image, int), removeImage(java.awt.Image, int, int, int)

removeImage

public void removeImage(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.

Parameters:

image - the image to be removed

id - the tracking ID frrom which to remove the image

Since:

JDK1.1

See Also:

removeImage(java.awt.Image), removeImage(java.awt.Image, int, int, int)

removeImage

public 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. Only the specified instance (with any duplicates) is removed.

Parameters:

image - the image to be removed

id - the tracking ID from which to remove the image

width - the width to remove (-1 for unscaled)

height - the height to remove (-1 for unscaled)

Since:

JDK1.1

See Also:

removeImage(java.awt.Image), removeImage(java.awt.Image, int)