MediaTracker (Java Platform SE 8 )
Keywords: java.awt.MediaTracker class
Date: 2020-03-26

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 `ImageObserver`s 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

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `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

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

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and 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 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 from 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)`

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