Remove some occurrences of dummy in core library

Remove occurrences in comments and private fields.

ISSUE: #7565
PiperOrigin-RevId: 320606558

extensions/ima/src/test/java/com/google/android/exoplayer2/ext/ima/ImaAdsLoaderTest.java

@@ -54,7 +54,7 @@ import com.google.android.exoplayer2.Player;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.Timeline.Period;
 import com.google.android.exoplayer2.ext.ima.ImaAdsLoader.ImaFactory;
-import com.google.android.exoplayer2.source.MaskingMediaSource.DummyTimeline;
+import com.google.android.exoplayer2.source.MaskingMediaSource.PlaceholderTimeline;
 import com.google.android.exoplayer2.source.ads.AdPlaybackState;
 import com.google.android.exoplayer2.source.ads.AdsLoader;
 import com.google.android.exoplayer2.source.ads.AdsMediaSource.AdLoadException;
@@ -170,7 +170,7 @@ public final class ImaAdsLoaderTest {
 
   @Test
   public void start_withPlaceholderContent_initializedAdsLoader() {
-    Timeline placeholderTimeline = new DummyTimeline(MediaItem.fromUri(Uri.EMPTY));
+    Timeline placeholderTimeline = new PlaceholderTimeline(MediaItem.fromUri(Uri.EMPTY));
     setupPlayback(placeholderTimeline, PREROLL_CUE_POINTS_SECONDS);
     imaAdsLoader.start(adsLoaderListener, adViewProvider);
 

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImplInternal.java

@@ -983,7 +983,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
       // The seek position was valid for the timeline that it was performed into, but the
       // timeline has changed or is not ready and a suitable seek position could not be resolved.
       Pair<MediaPeriodId, Long> firstPeriodAndPosition =
-          getDummyFirstMediaPeriodPosition(playbackInfo.timeline);
+          getPlaceholderFirstMediaPeriodPosition(playbackInfo.timeline);
       periodId = firstPeriodAndPosition.first;
       periodPositionUs = firstPeriodAndPosition.second;
       requestedContentPosition = C.TIME_UNSET;
@@ -1267,7 +1267,8 @@ import java.util.concurrent.atomic.AtomicBoolean;
     boolean resetTrackInfo = clearMediaSourceList;
     if (resetPosition) {
       pendingInitialSeekPosition = null;
-      Pair<MediaPeriodId, Long> firstPeriodAndPosition = getDummyFirstMediaPeriodPosition(timeline);
+      Pair<MediaPeriodId, Long> firstPeriodAndPosition =
+          getPlaceholderFirstMediaPeriodPosition(timeline);
       mediaPeriodId = firstPeriodAndPosition.first;
       startPositionUs = firstPeriodAndPosition.second;
       requestedContentPositionUs = C.TIME_UNSET;
@@ -1300,7 +1301,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
     }
   }
 
-  private Pair<MediaPeriodId, Long> getDummyFirstMediaPeriodPosition(Timeline timeline) {
+  private Pair<MediaPeriodId, Long> getPlaceholderFirstMediaPeriodPosition(Timeline timeline) {
     if (timeline.isEmpty()) {
       return Pair.create(PlaybackInfo.getDummyPeriodForEmptyTimeline(), 0L);
     }

library/core/src/main/java/com/google/android/exoplayer2/MediaPeriodHolder.java

@@ -380,7 +380,7 @@ import org.checkerframework.checker.nullness.compatqual.NullableType;
   }
 
   /**
-   * For each renderer of type {@link C#TRACK_TYPE_NONE}, we will remove the dummy {@link
+   * For each renderer of type {@link C#TRACK_TYPE_NONE}, we will remove the {@link
    * EmptySampleStream} that was associated with it.
    */
   private void disassociateNoSampleRenderersWithEmptySampleStream(
@@ -394,7 +394,7 @@ import org.checkerframework.checker.nullness.compatqual.NullableType;
 
   /**
    * For each renderer of type {@link C#TRACK_TYPE_NONE} that was enabled, we will associate it with
-   * a dummy {@link EmptySampleStream}.
+   * an {@link EmptySampleStream}.
    */
   private void associateNoSampleRenderersWithEmptySampleStream(
       @NullableType SampleStream[] sampleStreams) {

library/core/src/main/java/com/google/android/exoplayer2/PlaybackInfo.java

@@ -28,10 +28,10 @@ import com.google.android.exoplayer2.trackselection.TrackSelectorResult;
 /* package */ final class PlaybackInfo {
 
   /**
-   * Dummy media period id used while the timeline is empty and no period id is specified. This id
-   * is used when playback infos are created with {@link #createDummy(TrackSelectorResult)}.
+   * Placeholder media period id used while the timeline is empty and no period id is specified.
+   * This id is used when playback infos are created with {@link #createDummy(TrackSelectorResult)}.
    */
-  private static final MediaPeriodId DUMMY_MEDIA_PERIOD_ID =
+  private static final MediaPeriodId PLACEHOLDER_MEDIA_PERIOD_ID =
       new MediaPeriodId(/* periodUid= */ new Object());
 
   /** The current {@link Timeline}. */
@@ -81,24 +81,24 @@ import com.google.android.exoplayer2.trackselection.TrackSelectorResult;
   public volatile long positionUs;
 
   /**
-   * Creates empty dummy playback info which can be used for masking as long as no real playback
-   * info is available.
+   * Creates an empty placeholder playback info which can be used for masking as long as no real
+   * playback info is available.
    *
    * @param emptyTrackSelectorResult An empty track selector result with null entries for each
    *     renderer.
-   * @return A dummy playback info.
+   * @return A placeholder playback info.
    */
   public static PlaybackInfo createDummy(TrackSelectorResult emptyTrackSelectorResult) {
     return new PlaybackInfo(
         Timeline.EMPTY,
-        DUMMY_MEDIA_PERIOD_ID,
+        PLACEHOLDER_MEDIA_PERIOD_ID,
         /* requestedContentPositionUs= */ C.TIME_UNSET,
         Player.STATE_IDLE,
         /* playbackError= */ null,
         /* isLoading= */ false,
         TrackGroupArray.EMPTY,
         emptyTrackSelectorResult,
-        DUMMY_MEDIA_PERIOD_ID,
+        PLACEHOLDER_MEDIA_PERIOD_ID,
         /* playWhenReady= */ false,
         Player.PLAYBACK_SUPPRESSION_REASON_NONE,
         /* bufferedPositionUs= */ 0,
@@ -152,9 +152,9 @@ import com.google.android.exoplayer2.trackselection.TrackSelectorResult;
     this.positionUs = positionUs;
   }
 
-  /** Returns dummy period id for an empty timeline. */
+  /** Returns a placeholder period id for an empty timeline. */
   public static MediaPeriodId getDummyPeriodForEmptyTimeline() {
-    return DUMMY_MEDIA_PERIOD_ID;
+    return PLACEHOLDER_MEDIA_PERIOD_ID;
   }
 
   /**

library/core/src/main/java/com/google/android/exoplayer2/Timeline.java

@@ -124,7 +124,7 @@ public abstract class Timeline {
      */
     public static final Object SINGLE_WINDOW_UID = new Object();
 
-    private static final MediaItem DUMMY_MEDIA_ITEM =
+    private static final MediaItem EMPTY_MEDIA_ITEM =
         new MediaItem.Builder()
             .setMediaId("com.google.android.exoplayer2.Timeline")
             .setUri(Uri.EMPTY)
@@ -222,7 +222,7 @@ public abstract class Timeline {
     /** Creates window. */
     public Window() {
       uid = SINGLE_WINDOW_UID;
-      mediaItem = DUMMY_MEDIA_ITEM;
+      mediaItem = EMPTY_MEDIA_ITEM;
     }
 
     /** Sets the data held by this window. */
@@ -243,7 +243,7 @@ public abstract class Timeline {
         int lastPeriodIndex,
         long positionInFirstPeriodUs) {
       this.uid = uid;
-      this.mediaItem = mediaItem != null ? mediaItem : DUMMY_MEDIA_ITEM;
+      this.mediaItem = mediaItem != null ? mediaItem : EMPTY_MEDIA_ITEM;
       this.tag =
           mediaItem != null && mediaItem.playbackProperties != null
               ? mediaItem.playbackProperties.tag

library/core/src/main/java/com/google/android/exoplayer2/analytics/PlaybackStatsListener.java

@@ -150,7 +150,7 @@ public final class PlaybackStatsListener
     // TODO: Add AnalyticsListener.onAttachedToPlayer and onDetachedFromPlayer to auto-release with
     // an actual EventTime. Should also simplify other cases where the listener needs to be released
     // separately from the player.
-    EventTime dummyEventTime =
+    sessionManager.finishAllSessions(
         new EventTime(
             SystemClock.elapsedRealtime(),
             Timeline.EMPTY,
@@ -161,8 +161,7 @@ public final class PlaybackStatsListener
             /* currentWindowIndex= */ 0,
             /* currentMediaPeriodId= */ null,
             /* currentPlaybackPositionMs= */ 0,
-            /* totalBufferedDurationMs= */ 0);
-    sessionManager.finishAllSessions(dummyEventTime);
+            /* totalBufferedDurationMs= */ 0));
   }
 
   // PlaybackSessionManager.Listener implementation.

library/core/src/main/java/com/google/android/exoplayer2/audio/AudioRendererEventListener.java

@@ -98,12 +98,12 @@ public interface AudioRendererEventListener {
     @Nullable private final AudioRendererEventListener listener;
 
     /**
-     * @param handler A handler for dispatching events, or null if creating a dummy instance.
-     * @param listener The listener to which events should be dispatched, or null if creating a
-     *     dummy instance.
+     * @param handler A handler for dispatching events, or null if events should not be dispatched.
+     * @param listener The listener to which events should be dispatched, or null if events should
+     *     not be dispatched.
      */
-    public EventDispatcher(@Nullable Handler handler,
-        @Nullable AudioRendererEventListener listener) {
+    public EventDispatcher(
+        @Nullable Handler handler, @Nullable AudioRendererEventListener listener) {
       this.handler = listener != null ? Assertions.checkNotNull(handler) : null;
       this.listener = listener;
     }

library/core/src/main/java/com/google/android/exoplayer2/drm/OfflineLicenseHelper.java

@@ -34,7 +34,7 @@ import java.util.UUID;
 @RequiresApi(18)
 public final class OfflineLicenseHelper {
 
-  private static final DrmInitData DUMMY_DRM_INIT_DATA = new DrmInitData();
+  private static final DrmInitData EMPTY_DRM_INIT_DATA = new DrmInitData();
 
   private final ConditionVariable conditionVariable;
   private final DefaultDrmSessionManager drmSessionManager;
@@ -202,7 +202,7 @@ public final class OfflineLicenseHelper {
       throws DrmSessionException {
     Assertions.checkNotNull(offlineLicenseKeySetId);
     return blockingKeyRequest(
-        DefaultDrmSessionManager.MODE_DOWNLOAD, offlineLicenseKeySetId, DUMMY_DRM_INIT_DATA);
+        DefaultDrmSessionManager.MODE_DOWNLOAD, offlineLicenseKeySetId, EMPTY_DRM_INIT_DATA);
   }
 
   /**
@@ -215,7 +215,7 @@ public final class OfflineLicenseHelper {
       throws DrmSessionException {
     Assertions.checkNotNull(offlineLicenseKeySetId);
     blockingKeyRequest(
-        DefaultDrmSessionManager.MODE_RELEASE, offlineLicenseKeySetId, DUMMY_DRM_INIT_DATA);
+        DefaultDrmSessionManager.MODE_RELEASE, offlineLicenseKeySetId, EMPTY_DRM_INIT_DATA);
   }
 
   /**
@@ -231,7 +231,7 @@ public final class OfflineLicenseHelper {
     drmSessionManager.prepare();
     DrmSession drmSession =
         openBlockingKeyRequest(
-            DefaultDrmSessionManager.MODE_QUERY, offlineLicenseKeySetId, DUMMY_DRM_INIT_DATA);
+            DefaultDrmSessionManager.MODE_QUERY, offlineLicenseKeySetId, EMPTY_DRM_INIT_DATA);
     DrmSessionException error = drmSession.getError();
     Pair<Long, Long> licenseDurationRemainingSec =
         WidevineUtil.getLicenseDurationRemainingSec(drmSession);

library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadHelper.java

@@ -500,7 +500,7 @@ public final class DownloadHelper {
         new DefaultTrackSelector(trackSelectorParameters, new DownloadTrackSelection.Factory());
     this.rendererCapabilities = rendererCapabilities;
     this.scratchSet = new SparseIntArray();
-    trackSelector.init(/* listener= */ () -> {}, new DummyBandwidthMeter());
+    trackSelector.init(/* listener= */ () -> {}, new FakeBandwidthMeter());
     callbackHandler = Util.createHandlerForCurrentOrMainLooper();
     window = new Timeline.Window();
   }
@@ -1152,7 +1152,7 @@ public final class DownloadHelper {
     }
   }
 
-  private static final class DummyBandwidthMeter implements BandwidthMeter {
+  private static final class FakeBandwidthMeter implements BandwidthMeter {
 
     @Override
     public long getBitrateEstimate() {

library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java

@@ -56,7 +56,7 @@ public final class ConcatenatingMediaSource extends CompositeMediaSource<MediaSo
   private static final int MSG_UPDATE_TIMELINE = 4;
   private static final int MSG_ON_COMPLETION = 5;
 
-  private static final MediaItem DUMMY_MEDIA_ITEM =
+  private static final MediaItem EMPTY_MEDIA_ITEM =
       new MediaItem.Builder().setUri(Uri.EMPTY).build();
 
   // Accessed on any thread.
@@ -445,8 +445,8 @@ public final class ConcatenatingMediaSource extends CompositeMediaSource<MediaSo
   @Override
   public MediaItem getMediaItem() {
     // This method is actually never called because getInitialTimeline is implemented and hence the
-    // MaskingMediaSource does not need to create a dummy timeline for this media source.
-    return DUMMY_MEDIA_ITEM;
+    // MaskingMediaSource does not need to create a placeholder timeline for this media source.
+    return EMPTY_MEDIA_ITEM;
   }
 
   @Override
@@ -476,7 +476,7 @@ public final class ConcatenatingMediaSource extends CompositeMediaSource<MediaSo
     @Nullable MediaSourceHolder holder = mediaSourceByUid.get(mediaSourceHolderUid);
     if (holder == null) {
       // Stale event. The media source has already been removed.
-      holder = new MediaSourceHolder(new DummyMediaSource(), useLazyPreparation);
+      holder = new MediaSourceHolder(new FakeMediaSource(), useLazyPreparation);
       holder.isRemoved = true;
       prepareChildSource(holder, holder.mediaSource);
     }
@@ -988,8 +988,8 @@ public final class ConcatenatingMediaSource extends CompositeMediaSource<MediaSo
     }
   }
 
-  /** Dummy media source which does nothing and does not support creating periods. */
-  private static final class DummyMediaSource extends BaseMediaSource {
+  /** A media source which does nothing and does not support creating periods. */
+  private static final class FakeMediaSource extends BaseMediaSource {
 
     @Override
     protected void prepareSourceInternal(@Nullable TransferListener mediaTransferListener) {
@@ -998,7 +998,7 @@ public final class ConcatenatingMediaSource extends CompositeMediaSource<MediaSo
 
     @Override
     public MediaItem getMediaItem() {
-      return DUMMY_MEDIA_ITEM;
+      return EMPTY_MEDIA_ITEM;
     }
 
     @Override

library/core/src/main/java/com/google/android/exoplayer2/source/MaskingMediaSource.java

@@ -67,7 +67,7 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
               initialTimeline, /* firstWindowUid= */ null, /* firstPeriodUid= */ null);
       hasRealTimeline = true;
     } else {
-      timeline = MaskingTimeline.createWithDummyTimeline(mediaSource.getMediaItem());
+      timeline = MaskingTimeline.createWithPlaceholderTimeline(mediaSource.getMediaItem());
     }
   }
 
@@ -165,7 +165,9 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
           hasRealTimeline
               ? timeline.cloneWithUpdatedTimeline(newTimeline)
               : MaskingTimeline.createWithRealTimeline(
-                  newTimeline, Window.SINGLE_WINDOW_UID, MaskingTimeline.DUMMY_EXTERNAL_PERIOD_UID);
+                  newTimeline,
+                  Window.SINGLE_WINDOW_UID,
+                  MaskingTimeline.MASKING_EXTERNAL_PERIOD_UID);
     } else {
       // Determine first period and the start position.
       // This will be:
@@ -174,7 +176,7 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
       //     a non-zero initial seek position in the window.
       //  3. The default window start position if the deferred period has a prepare position of zero
       //     under the assumption that the prepare position of zero was used because it's the
-      //     default position of the DummyTimeline window. Note that this will override an
+      //     default position of the PlaceholderTimeline window. Note that this will override an
       //     intentional seek to zero for a window with a non-zero default position. This is
       //     unlikely to be a problem as a non-zero default position usually only occurs for live
       //     playbacks and seeking to zero in a live window would cause BehindLiveWindowExceptions
@@ -230,7 +232,7 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
 
   private Object getInternalPeriodUid(Object externalPeriodUid) {
     return timeline.replacedInternalPeriodUid != null
-            && externalPeriodUid.equals(MaskingTimeline.DUMMY_EXTERNAL_PERIOD_UID)
+            && externalPeriodUid.equals(MaskingTimeline.MASKING_EXTERNAL_PERIOD_UID)
         ? timeline.replacedInternalPeriodUid
         : externalPeriodUid;
   }
@@ -238,7 +240,7 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
   private Object getExternalPeriodUid(Object internalPeriodUid) {
     return timeline.replacedInternalPeriodUid != null
             && timeline.replacedInternalPeriodUid.equals(internalPeriodUid)
-        ? MaskingTimeline.DUMMY_EXTERNAL_PERIOD_UID
+        ? MaskingTimeline.MASKING_EXTERNAL_PERIOD_UID
         : internalPeriodUid;
   }
 
@@ -265,34 +267,36 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
 
   /**
    * Timeline used as placeholder for an unprepared media source. After preparation, a
-   * MaskingTimeline is used to keep the originally assigned dummy period ID.
+   * MaskingTimeline is used to keep the originally assigned masking period ID.
    */
   private static final class MaskingTimeline extends ForwardingTimeline {
 
-    public static final Object DUMMY_EXTERNAL_PERIOD_UID = new Object();
+    public static final Object MASKING_EXTERNAL_PERIOD_UID = new Object();
 
     @Nullable private final Object replacedInternalWindowUid;
     @Nullable private final Object replacedInternalPeriodUid;
 
     /**
-     * Returns an instance with a dummy timeline using the provided {@link MediaItem}.
+     * Returns an instance with a placeholder timeline using the provided {@link MediaItem}.
      *
      * @param mediaItem A {@link MediaItem}.
      */
-    public static MaskingTimeline createWithDummyTimeline(MediaItem mediaItem) {
+    public static MaskingTimeline createWithPlaceholderTimeline(MediaItem mediaItem) {
       return new MaskingTimeline(
-          new DummyTimeline(mediaItem), Window.SINGLE_WINDOW_UID, DUMMY_EXTERNAL_PERIOD_UID);
+          new PlaceholderTimeline(mediaItem),
+          Window.SINGLE_WINDOW_UID,
+          MASKING_EXTERNAL_PERIOD_UID);
     }
 
     /**
      * Returns an instance with a real timeline, replacing the provided period ID with the already
-     * assigned dummy period ID.
+     * assigned masking period ID.
      *
      * @param timeline The real timeline.
      * @param firstWindowUid The window UID in the timeline which will be replaced by the already
      *     assigned {@link Window#SINGLE_WINDOW_UID}.
      * @param firstPeriodUid The period UID in the timeline which will be replaced by the already
-     *     assigned {@link #DUMMY_EXTERNAL_PERIOD_UID}.
+     *     assigned {@link #MASKING_EXTERNAL_PERIOD_UID}.
      */
     public static MaskingTimeline createWithRealTimeline(
         Timeline timeline, @Nullable Object firstWindowUid, @Nullable Object firstPeriodUid) {
@@ -335,7 +339,7 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
     public Period getPeriod(int periodIndex, Period period, boolean setIds) {
       timeline.getPeriod(periodIndex, period, setIds);
       if (Util.areEqual(period.uid, replacedInternalPeriodUid) && setIds) {
-        period.uid = DUMMY_EXTERNAL_PERIOD_UID;
+        period.uid = MASKING_EXTERNAL_PERIOD_UID;
       }
       return period;
     }
@@ -343,7 +347,7 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
     @Override
     public int getIndexOfPeriod(Object uid) {
       return timeline.getIndexOfPeriod(
-          DUMMY_EXTERNAL_PERIOD_UID.equals(uid) && replacedInternalPeriodUid != null
+          MASKING_EXTERNAL_PERIOD_UID.equals(uid) && replacedInternalPeriodUid != null
               ? replacedInternalPeriodUid
               : uid);
     }
@@ -351,18 +355,18 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
     @Override
     public Object getUidOfPeriod(int periodIndex) {
       Object uid = timeline.getUidOfPeriod(periodIndex);
-      return Util.areEqual(uid, replacedInternalPeriodUid) ? DUMMY_EXTERNAL_PERIOD_UID : uid;
+      return Util.areEqual(uid, replacedInternalPeriodUid) ? MASKING_EXTERNAL_PERIOD_UID : uid;
     }
   }
 
-  /** Dummy placeholder timeline with one dynamic window with a period of indeterminate duration. */
+  /** A timeline with one dynamic window with a period of indeterminate duration. */
   @VisibleForTesting
-  public static final class DummyTimeline extends Timeline {
+  public static final class PlaceholderTimeline extends Timeline {
 
     private final MediaItem mediaItem;
 
     /** Creates a new instance with the given media item. */
-    public DummyTimeline(MediaItem mediaItem) {
+    public PlaceholderTimeline(MediaItem mediaItem) {
       this.mediaItem = mediaItem;
     }
 
@@ -402,7 +406,7 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
     public Period getPeriod(int periodIndex, Period period, boolean setIds) {
       return period.set(
           /* id= */ setIds ? 0 : null,
-          /* uid= */ setIds ? MaskingTimeline.DUMMY_EXTERNAL_PERIOD_UID : null,
+          /* uid= */ setIds ? MaskingTimeline.MASKING_EXTERNAL_PERIOD_UID : null,
           /* windowIndex= */ 0,
           /* durationUs = */ C.TIME_UNSET,
           /* positionInWindowUs= */ 0);
@@ -410,12 +414,12 @@ public final class MaskingMediaSource extends CompositeMediaSource<Void> {
 
     @Override
     public int getIndexOfPeriod(Object uid) {
-      return uid == MaskingTimeline.DUMMY_EXTERNAL_PERIOD_UID ? 0 : C.INDEX_UNSET;
+      return uid == MaskingTimeline.MASKING_EXTERNAL_PERIOD_UID ? 0 : C.INDEX_UNSET;
     }
 
     @Override
     public Object getUidOfPeriod(int periodIndex) {
-      return MaskingTimeline.DUMMY_EXTERNAL_PERIOD_UID;
+      return MaskingTimeline.MASKING_EXTERNAL_PERIOD_UID;
     }
   }
 }

library/core/src/main/java/com/google/android/exoplayer2/source/MediaSource.java

@@ -93,8 +93,8 @@ public interface MediaSource {
     public final int nextAdGroupIndex;
 
     /**
-     * Creates a media period identifier for a dummy period which is not part of a buffered sequence
-     * of windows.
+     * Creates a media period identifier for a period which is not part of a buffered sequence of
+     * windows.
      *
      * @param periodUid The unique id of the timeline period.
      */
@@ -248,8 +248,8 @@ public interface MediaSource {
   void removeDrmEventListener(DrmSessionEventListener eventListener);
 
   /**
-   * Returns the initial dummy timeline that is returned immediately when the real timeline is not
-   * yet known, or null to let the player create an initial timeline.
+   * Returns the initial placeholder timeline that is returned immediately when the real timeline is
+   * not yet known, or null to let the player create an initial timeline.
    *
    * <p>The initial timeline must use the same uids for windows and periods that the real timeline
    * will use. It also must provide windows which are marked as dynamic to indicate that the window

library/core/src/main/java/com/google/android/exoplayer2/source/MergingMediaSource.java

@@ -66,7 +66,7 @@ public final class MergingMediaSource extends CompositeMediaSource<Integer> {
   }
 
   private static final int PERIOD_COUNT_UNSET = -1;
-  private static final MediaItem DUMMY_MEDIA_ITEM =
+  private static final MediaItem EMPTY_MEDIA_ITEM =
       new MediaItem.Builder().setMediaId("MergingMediaSource").build();
 
   private final boolean adjustPeriodTimeOffsets;
@@ -137,7 +137,7 @@ public final class MergingMediaSource extends CompositeMediaSource<Integer> {
 
   @Override
   public MediaItem getMediaItem() {
-    return mediaSources.length > 0 ? mediaSources[0].getMediaItem() : DUMMY_MEDIA_ITEM;
+    return mediaSources.length > 0 ? mediaSources[0].getMediaItem() : EMPTY_MEDIA_ITEM;
   }
 
   @Override

library/core/src/main/java/com/google/android/exoplayer2/source/ads/AdsMediaSource.java

@@ -121,7 +121,7 @@ public final class AdsMediaSource extends CompositeMediaSource<MediaPeriodId> {
   }
 
   // Used to identify the content "child" source for CompositeMediaSource.
-  private static final MediaPeriodId DUMMY_CONTENT_MEDIA_PERIOD_ID =
+  private static final MediaPeriodId CHILD_SOURCE_MEDIA_PERIOD_ID =
       new MediaPeriodId(/* periodUid= */ new Object());
 
   private final MediaSource contentMediaSource;
@@ -203,7 +203,7 @@ public final class AdsMediaSource extends CompositeMediaSource<MediaPeriodId> {
     super.prepareSourceInternal(mediaTransferListener);
     ComponentListener componentListener = new ComponentListener();
     this.componentListener = componentListener;
-    prepareChildSource(DUMMY_CONTENT_MEDIA_PERIOD_ID, contentMediaSource);
+    prepareChildSource(CHILD_SOURCE_MEDIA_PERIOD_ID, contentMediaSource);
     mainHandler.post(() -> adsLoader.start(componentListener, adViewProvider));
   }
 
@@ -284,8 +284,8 @@ public final class AdsMediaSource extends CompositeMediaSource<MediaPeriodId> {
   @Override
   protected MediaPeriodId getMediaPeriodIdForChildMediaPeriodId(
       MediaPeriodId childId, MediaPeriodId mediaPeriodId) {
-    // The child id for the content period is just DUMMY_CONTENT_MEDIA_PERIOD_ID. That's why we need
-    // to forward the reported mediaPeriodId in this case.
+    // The child id for the content period is just CHILD_SOURCE_MEDIA_PERIOD_ID. That's why
+    // we need to forward the reported mediaPeriodId in this case.
     return childId.isAd() ? childId : mediaPeriodId;
   }
 

library/core/src/main/java/com/google/android/exoplayer2/source/chunk/BundledChunkExtractor.java

@@ -41,7 +41,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
  */
 public final class BundledChunkExtractor implements ExtractorOutput, ChunkExtractor {
 
-  private static final PositionHolder DUMMY_POSITION_HOLDER = new PositionHolder();
+  private static final PositionHolder POSITION_HOLDER = new PositionHolder();
 
   private final Extractor extractor;
   private final int primaryTrackType;
@@ -106,7 +106,7 @@ public final class BundledChunkExtractor implements ExtractorOutput, ChunkExtrac
 
   @Override
   public boolean read(ExtractorInput input) throws IOException {
-    int result = extractor.read(input, DUMMY_POSITION_HOLDER);
+    int result = extractor.read(input, POSITION_HOLDER);
     Assertions.checkState(result != Extractor.RESULT_SEEK);
     return result == Extractor.RESULT_CONTINUE;
   }
@@ -149,7 +149,7 @@ public final class BundledChunkExtractor implements ExtractorOutput, ChunkExtrac
     private final int id;
     private final int type;
     @Nullable private final Format manifestFormat;
-    private final DummyTrackOutput dummyTrackOutput;
+    private final DummyTrackOutput fakeTrackOutput;
 
     public @MonotonicNonNull Format sampleFormat;
     private @MonotonicNonNull TrackOutput trackOutput;
@@ -159,12 +159,12 @@ public final class BundledChunkExtractor implements ExtractorOutput, ChunkExtrac
       this.id = id;
       this.type = type;
       this.manifestFormat = manifestFormat;
-      dummyTrackOutput = new DummyTrackOutput();
+      fakeTrackOutput = new DummyTrackOutput();
     }
 
     public void bind(@Nullable TrackOutputProvider trackOutputProvider, long endTimeUs) {
       if (trackOutputProvider == null) {
-        trackOutput = dummyTrackOutput;
+        trackOutput = fakeTrackOutput;
         return;
       }
       this.endTimeUs = endTimeUs;
@@ -201,7 +201,7 @@ public final class BundledChunkExtractor implements ExtractorOutput, ChunkExtrac
         int offset,
         @Nullable CryptoData cryptoData) {
       if (endTimeUs != C.TIME_UNSET && timeUs >= endTimeUs) {
-        trackOutput = dummyTrackOutput;
+        trackOutput = fakeTrackOutput;
       }
       castNonNull(trackOutput).sampleMetadata(timeUs, flags, size, offset, cryptoData);
     }

library/core/src/main/java/com/google/android/exoplayer2/upstream/DummyDataSource.java

@@ -19,9 +19,7 @@ import android.net.Uri;
 import androidx.annotation.Nullable;
 import java.io.IOException;
 
-/**
- * A dummy DataSource which provides no data. {@link #open(DataSpec)} throws {@link IOException}.
- */
+/** A DataSource which provides no data. {@link #open(DataSpec)} throws {@link IOException}. */
 public final class DummyDataSource implements DataSource {
 
   public static final DummyDataSource INSTANCE = new DummyDataSource();
@@ -38,7 +36,7 @@ public final class DummyDataSource implements DataSource {
 
   @Override
   public long open(DataSpec dataSpec) throws IOException {
-    throw new IOException("Dummy source");
+    throw new IOException("DummyDataSource cannot be opened");
   }
 
   @Override

library/core/src/main/java/com/google/android/exoplayer2/video/DummySurface.java

@@ -22,7 +22,6 @@ import static com.google.android.exoplayer2.util.EGLSurfaceTexture.SECURE_MODE_S
 import android.content.Context;
 import android.graphics.SurfaceTexture;
 import android.os.Handler;
-import android.os.Handler.Callback;
 import android.os.HandlerThread;
 import android.os.Message;
 import android.view.Surface;
@@ -70,14 +69,14 @@ public final class DummySurface extends Surface {
   /**
    * Returns a newly created dummy surface. The surface must be released by calling {@link #release}
    * when it's no longer required.
-   * <p>
-   * Must only be called if {@link Util#SDK_INT} is 17 or higher.
+   *
+   * <p>Must only be called if {@link Util#SDK_INT} is 17 or higher.
    *
    * @param context Any {@link Context}.
-   * @param secure Whether a secure surface is required. Must only be requested if
-   *     {@link #isSecureSupported(Context)} returns {@code true}.
-   * @throws IllegalStateException If a secure surface is requested on a device for which
-   *     {@link #isSecureSupported(Context)} returns {@code false}.
+   * @param secure Whether a secure surface is required. Must only be requested if {@link
+   *     #isSecureSupported(Context)} returns {@code true}.
+   * @throws IllegalStateException If a secure surface is requested on a device for which {@link
+   *     #isSecureSupported(Context)} returns {@code false}.
    */
   public static DummySurface newInstanceV17(Context context, boolean secure) {
     Assertions.checkState(!secure || isSecureSupported(context));
@@ -123,7 +122,7 @@ public final class DummySurface extends Surface {
     }
   }
 
-  private static class DummySurfaceThread extends HandlerThread implements Callback {
+  private static class DummySurfaceThread extends HandlerThread implements Handler.Callback {
 
     private static final int MSG_INIT = 1;
     private static final int MSG_RELEASE = 2;

library/core/src/main/java/com/google/android/exoplayer2/video/VideoRendererEventListener.java

@@ -138,12 +138,12 @@ public interface VideoRendererEventListener {
     @Nullable private final VideoRendererEventListener listener;
 
     /**
-     * @param handler A handler for dispatching events, or null if creating a dummy instance.
-     * @param listener The listener to which events should be dispatched, or null if creating a
-     *     dummy instance.
+     * @param handler A handler for dispatching events, or null if events should not be dispatched.
+     * @param listener The listener to which events should be dispatched, or null if events should
+     *     not be dispatched.
      */
-    public EventDispatcher(@Nullable Handler handler,
-        @Nullable VideoRendererEventListener listener) {
+    public EventDispatcher(
+        @Nullable Handler handler, @Nullable VideoRendererEventListener listener) {
       this.handler = listener != null ? Assertions.checkNotNull(handler) : null;
       this.listener = listener;
     }

library/core/src/test/java/com/google/android/exoplayer2/analytics/AnalyticsCollectorTest.java

@@ -786,7 +786,7 @@ public final class AnalyticsCollectorTest {
     assertThat(listener.getEvents(EVENT_TIMELINE_CHANGED))
         .containsExactly(
             WINDOW_0 /* PLAYLIST_CHANGED */,
-            window0Period1Seq0 /* SOURCE_UPDATE (concatenated timeline replaces dummy) */,
+            window0Period1Seq0 /* SOURCE_UPDATE (concatenated timeline replaces placeholder) */,
             period1Seq0 /* SOURCE_UPDATE (child sources in concatenating source moved) */)
         .inOrder();
     assertThat(listener.getEvents(EVENT_LOADING_CHANGED))

library/core/src/test/java/com/google/android/exoplayer2/database/VersionTableTest.java

@@ -94,7 +94,7 @@ public class VersionTableTest {
   @Test
   public void doesTableExist_existingTable_returnsTrue() {
     String table = "TestTable";
-    databaseProvider.getWritableDatabase().execSQL("CREATE TABLE " + table + " (dummy INTEGER)");
+    databaseProvider.getWritableDatabase().execSQL("CREATE TABLE " + table + " (test INTEGER)");
     assertThat(VersionTable.tableExists(database, table)).isTrue();
   }
 }

library/core/src/test/java/com/google/android/exoplayer2/offline/DownloadManagerTest.java

@@ -56,7 +56,7 @@ public class DownloadManagerTest {
   private static final int APP_STOP_REASON = 1;
   /** The minimum number of times a download must be retried before failing. */
   private static final int MIN_RETRY_COUNT = 3;
-  /** Dummy value for the current time. */
+  /** Test value for the current time. */
   private static final long NOW_MS = 1234;
 
   private static final String ID1 = "id1";
@@ -68,19 +68,19 @@ public class DownloadManagerTest {
 
   private DownloadManager downloadManager;
   private TestDownloadManagerListener downloadManagerListener;
-  private DummyMainThread dummyMainThread;
+  private DummyMainThread testThread;
 
   @Before
   public void setUp() throws Exception {
     ShadowLog.stream = System.out;
-    dummyMainThread = new DummyMainThread();
+    testThread = new DummyMainThread();
     setupDownloadManager(/* maxParallelDownloads= */ 100);
   }
 
   @After
   public void tearDown() throws Exception {
     releaseDownloadManager();
-    dummyMainThread.release();
+    testThread.release();
   }
 
   @Test
@@ -728,7 +728,7 @@ public class DownloadManagerTest {
   }
 
   private void runOnMainThread(TestRunnable r) {
-    dummyMainThread.runTestOnMainThread(r);
+    testThread.runTestOnMainThread(r);
   }
 
   private FakeDownloader getDownloaderAt(int index) throws InterruptedException {

library/core/src/test/java/com/google/android/exoplayer2/source/ClippingMediaSourceTest.java

@@ -30,7 +30,7 @@ import com.google.android.exoplayer2.Timeline.Window;
 import com.google.android.exoplayer2.drm.DrmSessionEventListener;
 import com.google.android.exoplayer2.drm.DrmSessionManager;
 import com.google.android.exoplayer2.source.ClippingMediaSource.IllegalClippingException;
-import com.google.android.exoplayer2.source.MaskingMediaSource.DummyTimeline;
+import com.google.android.exoplayer2.source.MaskingMediaSource.PlaceholderTimeline;
 import com.google.android.exoplayer2.source.MediaSource.MediaPeriodId;
 import com.google.android.exoplayer2.testutil.FakeMediaPeriod;
 import com.google.android.exoplayer2.testutil.FakeMediaSource;
@@ -173,7 +173,7 @@ public final class ClippingMediaSourceTest {
     // Timeline that's dynamic and not seekable. A child source might report such a timeline prior
     // to it having loaded sufficient data to establish its duration and seekability. Such timelines
     // should not result in clipping failure.
-    Timeline timeline = new DummyTimeline(MediaItem.fromUri(Uri.EMPTY));
+    Timeline timeline = new PlaceholderTimeline(MediaItem.fromUri(Uri.EMPTY));
 
     Timeline clippedTimeline =
         getClippedTimeline(

library/core/src/test/java/com/google/android/exoplayer2/source/SampleQueueTest.java

@@ -123,7 +123,7 @@ public final class SampleQueueTest {
   private static final int[] ENCRYPTED_SAMPLE_OFFSETS = new int[] {7, 4, 3, 0};
   private static final byte[] ENCRYPTED_SAMPLE_DATA = new byte[] {1, 1, 1, 1, 1, 1, 1, 1};
 
-  private static final TrackOutput.CryptoData DUMMY_CRYPTO_DATA =
+  private static final TrackOutput.CryptoData CRYPTO_DATA =
       new TrackOutput.CryptoData(C.CRYPTO_MODE_AES_CTR, new byte[16], 0, 0);
 
   private Allocator allocator;
@@ -1205,7 +1205,7 @@ public final class SampleQueueTest {
           sampleFlags[i],
           sampleSizes[i],
           sampleOffsets[i],
-          (sampleFlags[i] & C.BUFFER_FLAG_ENCRYPTED) != 0 ? DUMMY_CRYPTO_DATA : null);
+          (sampleFlags[i] & C.BUFFER_FLAG_ENCRYPTED) != 0 ? CRYPTO_DATA : null);
     }
   }
 
@@ -1222,7 +1222,7 @@ public final class SampleQueueTest {
         sampleFlags,
         data.length,
         /* offset= */ 0,
-        (sampleFlags & C.BUFFER_FLAG_ENCRYPTED) != 0 ? DUMMY_CRYPTO_DATA : null);
+        (sampleFlags & C.BUFFER_FLAG_ENCRYPTED) != 0 ? CRYPTO_DATA : null);
   }
 
   /**

library/core/src/test/java/com/google/android/exoplayer2/upstream/DefaultBandwidthMeterTest.java

@@ -569,7 +569,7 @@ public final class DefaultBandwidthMeterTest {
     long[] bitrateEstimates = new long[SIMULATED_TRANSFER_COUNT];
     Random random = new Random(/* seed= */ 0);
     DataSource dataSource = new FakeDataSource();
-    DataSpec dataSpec = new DataSpec(Uri.parse("https://dummy.com"));
+    DataSpec dataSpec = new DataSpec(Uri.parse("https://test.com"));
     for (int i = 0; i < SIMULATED_TRANSFER_COUNT; i++) {
       bandwidthMeter.onTransferStart(dataSource, dataSpec, /* isNetwork= */ true);
       clock.advanceTime(random.nextInt(/* bound= */ 5000));