Module java.desktop
Package 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:
1.0
See Also:

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    ABORTED
    Flag indicating that the downloading of media was aborted.
    static final int
    COMPLETE
    Flag indicating that the downloading of media was completed successfully.
    static final int
    ERRORED
    Flag indicating that the downloading of media encountered an error.
    static final int
    LOADING
    Flag indicating that media is currently being loaded.

  • Constructor Summary

    Constructors
    Constructor
    Description
    MediaTracker(Component comp)
    Creates a media tracker to track images for a given component.

  • Method Summary

    Modifier and Type
    Method
    Description
    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 declared in class java.lang.Object

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

  • Field Details

  • Constructor Details

    • 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 Details

    • 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

      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:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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

      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:

    • 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:

    • 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:

    • 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:

    • 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
      Returns:
      true if the loading completed in time; otherwise false
      Throws:
      InterruptedException - if any thread has interrupted this thread.
      See Also:

    • 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:

    • 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:
      1.1
      See Also:

    • 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 from which to remove the image
      Since:
      1.1
      See Also:

    • 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:
      1.1
      See Also: