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§1.28 Class MediaTracker
public class java.awt.MediaTracker
extends java.lang.Object (I-§1.12)
{
// Fields
public final static int ABORTED; §1.28.1
public final static int COMPLETE; §1.28.2
public final static int ERRORED; §1.28.3
public final static int LOADING; §1.28.4
// Constructors
public MediaTracker(Component comp); §1.28.5
// Methods
public void addImage(Image image, int id); §1.28.6
public void addImage(Image image, int id, int w, int h); §1.28.7
public boolean checkAll(); §1.28.8
public boolean checkAll(boolean load); §1.28.9
public boolean checkID(int id); §1.28.10
public boolean checkID(int id, boolean load); §1.28.11
public Object[] getErrorsAny(); §1.28.12
public Object[] getErrorsID(int id); §1.28.13
public boolean isErrorAny(); §1.28.14
public boolean isErrorID(int id); §1.28.15
public int statusAll(boolean load); §1.28.16
public int statusID(int id, boolean load); §1.28.17
public void waitForAll(); §1.28.18
public boolean waitForAll(long ms); §1.28.19
public void waitForID(int id); §1.28.20
public boolean waitForID(int id, long ms); §1.28.21
}
The MediaTracker class is a utility class to trace 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 the media tracker, create an instance of the MediaTracker class and then call the
addImage method (II-§1.28.6) for each image to be tracked. In addition each image can be
assigned a unique identifier. The identifier controls both the priority order in which the
images are fetched as well as identifying 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.
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
// Media Tracker
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 point. 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() &&
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) &&
MediaTracker.COMPLETE) != 0) {
g.drawImage(anim[index], 10, 10, this);
}
}
}
ABORTED
public final static int ABORTED = 2
- Flag indicating the download of some media was aborted.
- See Also:
- statusAll (II-§1.28.16)
statusID (II-§1.28.17).
COMPLETE
public final static int COMPLETE = 8
- Flag indicating the download of media completed successfully.
- See Also:
- statusAll (II-§1.28.16)
statusID (II-§1.28.17).
ERRORED
public final static int ERRORED = 4
- Flag indicating the download of some media encountered an error.
- See Also:
- statusAll (II-§1.28.16)
statusID (II-§1.28.17).
LOADING
public final static int LOADING = 1
- Flag indicating some media is currently being loaded.
- See Also:
- statusAll (II-§1.28.16)
statusID (II-§1.28.17).
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 by this media tracker.
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 by this media
tracker. The image will eventually be rendered at the indicated width and
height.
- Parameters:
image
-
the image to be tracked
id
-
the identifier used to later track this image
w
-
the width at which the image will be rendered
h
-
the height at which the image will be 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 method
(II-§1.28.14) or isErrorID method (II-§1.28.15) to check for errors.
- Returns:
- true if all images have finished loading, were aborted or encountered
an error; false otherwise.
- See Also:
- checkID (II-§1.28.10) .
checkAll
public boolean checkAll(boolean load)
- Checks to see if all images being tracked by this media tracker have finished loading.
- If the load flag is true, then start 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 method
(II-§1.28.14) or isErrorID method (II-§1.28.15) 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, were aborted or encountered
an error; false otherwise.
- See Also:
- checkID (II-§1.28.11).
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 method
(II-§1.28.14) or isErrorID method (II-§1.28.15) to check for errors.
- Parameters:
id
-
the identifier of the images to check.
- Returns:
- true if all images have finished loading, were aborted or encountered
an error; false otherwise.
- See Also:
- checkAll (II-§1.28.8).
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 load flag is true, then start 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 tohave finished loading. Use the isErrorAny method
(II-§1.28.14) or isErrorID method (II-§1.28.15) 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, were aborted or encountered
an error; false otherwise.
- See Also:
- checkAll (II-§1.28.8).
getErrorsAny
public Object[] getErrorsAny()
- 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 (II-§1.28.14)
getErrorsID (II-§1.28.13).
getErrorsID
public Object[] getErrorsID(int id)
- Parameters:
id
-
the identifier of the images to check
- Returns:
- an array of media objects tracked by this media tracker with the specified identifer that have encountered an error, or null if there are none
with errors.
- See Also:
- isErrorID (II-§1.28.15)
getErrorsAny (II-§1.28.12).
isErrorAny
public boolean isErrorAny()
- Returns:
- true if any of the images tracked by this media tracker had an error during loading; false otherwise.
- See Also:
- isErrorID (II-§1.28.15)
getErrorsAny (II-§1.28.12).
isErrorID
public boolean isErrorID(int id)
- Checks the error status of all of the images tracked by this media tracker
with the specified ID.
- 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 (II-§1.28.14)
getErrorsID (II-§1.28.13).
statusAll
public int statusAll(boolean load)
- Calculates and returns the bitwise inclusive OR of the status of all the
media being tracked by this media tracker. The possible flags are specified
by the following four constants:
- An image that hasn't started loading has zero as its status.
- If the load flag is true, then start 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 (II-§1.28.17).
statusID
public int statusID(int id, boolean load)
- Calculates and returns the bitwise inclusive OR of the status of all the
media tracked by this media tracker with the specified identifier. The possible flags are as above in the statusAll method (II-§1.28.16). An image that
hasn't started loading has zero as its status.
- If the load flag is true, then start 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 being
tracked.
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 finished loading. Use the isErrorAny method (II-§1.28.14) or
isErrorID method (II-§1.28.15) to check for errors.
- Throws
- InterruptedException (I-§1.37)
- If another thread has interrupted this thread.
- See Also:
- waitForID (II-§1.28.20).
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 have passed.
- If there is an error while loading or scaling an image then that image is
considered finished loading. Use the isErrorAny method (II-§1.28.14) or
isErrorID method (II-§1.28.15) 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 (I-§1.37)
- If another thread has interrupted this thread.
- See Also:
- waitForID (II-§1.28.21).
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 finished loading. Use the isErrorAny method (II-§1.28.14) or
isErrorID method (II-§1.28.15) to check for errors.
- Parameters:
id
-
the identifier of the images to check
- Throws
- InterruptedException (I-§1.37)
- If another thread has interrupted this thread.
- See Also:
- waitForAll (II-§1.28.18).
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 have passed
- If there is an error while loading or scaling an image then that image is
considered finished loading. Use the isErrorAny method (II-§1.28.14) or
isErrorID method (II-§1.28.15) to check for errors.
- Parameters:
id
-
the identifier of the images to check
ms
-
the number of milliseconds to wait for the loading to complete
- Returns:
- true if all images were successfully loaded; false otherwise.
- Throws
- InterruptedException (I-§1.37)
- If another thread has interrupted this thread.
- See Also:
- waitForAll (II-§1.28.19).
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Java API Document (HTML generated by dkramer on April 22, 1996)
Copyright © 1996 Sun Microsystems, Inc.
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Please send any comments or corrections to doug.kramer@sun.com