+ * Adds an album to this album.
+ *
+ * @param album
+ * The album to add
+ */
+ public void addAlbum(Album album) {
+ checkNotNull(album, "album must not be null");
+ checkArgument(album.getSone().equals(sone), "album must belong to the same Sone as this album");
+ checkState((this.parent == null) || (this.parent.equals(album.parent)), "album must not already be set to some other Sone");
+ album.setParent(this);
+ if (!albums.contains(album)) {
+ albums.add(album);
+ }
+ }
+
+ /**
+ * Removes an album from this album.
+ *
+ * @param album
+ * The album to remove
+ */
+ public void removeAlbum(Album album) {
+ checkNotNull(album, "album must not be null");
+ checkArgument(album.sone.equals(sone), "album must belong this album’s Sone");
+ checkArgument(equals(album.parent), "album must belong to this album");
+ albums.remove(album);
+ album.removeParent();
+ }
+
+ /**
+ * Moves the given album up in this album’s albums. If the album is already
+ * the first album, nothing happens.
+ *
+ * @param album
+ * The album to move up
+ * @return The album that the given album swapped the place with, or
+ * <code>null</code> if the album did not change its place
+ */
+ public Album moveAlbumUp(Album album) {
+ checkNotNull(album, "album must not be null");
+ checkArgument(album.sone.equals(sone), "album must belong to the same Sone as this album");
+ checkArgument(equals(album.parent), "album must belong to this album");
+ int oldIndex = albums.indexOf(album);
+ if (oldIndex <= 0) {
+ return null;
+ }
+ albums.remove(oldIndex);
+ albums.add(oldIndex - 1, album);
+ return albums.get(oldIndex);
+ }
+
+ /**
+ * Moves the given album down in this album’s albums. If the album is
+ * already the last album, nothing happens.
+ *
+ * @param album
+ * The album to move down
+ * @return The album that the given album swapped the place with, or
+ * <code>null</code> if the album did not change its place
+ */
+ public Album moveAlbumDown(Album album) {
+ checkNotNull(album, "album must not be null");
+ checkArgument(album.sone.equals(sone), "album must belong to the same Sone as this album");
+ checkArgument(equals(album.parent), "album must belong to this album");
+ int oldIndex = albums.indexOf(album);
+ if ((oldIndex < 0) || (oldIndex >= (albums.size() - 1))) {
+ return null;
+ }
+ albums.remove(oldIndex);
+ albums.add(oldIndex + 1, album);
+ return albums.get(oldIndex);
+ }
+
+ /**