this.header = new AvlNode<>();
    successor(header, header);
    this.rootReference = new Reference<>();
  }

  /** A function which can be summed across a subtree. */
  private enum Aggregate {
    SIZE {
      @Override
      int nodeAggregate(AvlNode<?> node) {
        return node.elemCount;
      }

      @Override
      long treeAggregate(@Nullable AvlNode<?> root) {

   * double[])}.
   *
   * @since 2.0
   */
  public static Comparator<double[]> lexicographicalComparator() {
    return LexicographicalComparator.INSTANCE;
  }

  private enum LexicographicalComparator implements Comparator<double[]> {
    INSTANCE;

    @Override
    public int compare(double[] left, double[] right) {
      int minLength = Math.min(left.length, right.length);

      /*
       * The result has the same type argument we started with. We just couldn't express EnumSet<E>
       * or ImmutableEnumSet<E> along the way because our own <E> isn't <E extends Enum<E>>.
       *
       * We are also performing a safe covariant cast to change <? extends E> to <E>.
       */
      @SuppressWarnings("unchecked")
      ImmutableSet<E> result = (ImmutableSet<E>) untypedResult;

   * Returns a predicate that returns the result of {@link File#isFile} on input files.
   *
   * @since 15.0
   */
  public static Predicate<File> isFile() {
    return FilePredicate.IS_FILE;
  }

  private enum FilePredicate implements Predicate<File> {
    IS_DIRECTORY {
      @Override
      public boolean apply(File file) {
        return file.isDirectory();
      }

      @Override

          queueIterator.remove();
        }
      }
      assertThat(remaining).isEqualTo(0);
      assertIntact(queue);
      assertThat(queue).containsExactlyElementsIn(elements);
    }
  }

  private enum Element {
    ONE,
    TWO,
    THREE,
    FOUR,
    FIVE;
  }

  public void testRandomAddsAndRemoves_duplicateElements() {
    Random random = new Random(0);

          protected void verify(List<Integer> elements) {
            assertEquals(new HashSet<>(elements), multimap.get("foo"));
          }
        };

    tester.test();
  }

  private enum Color {
    BLUE,
    RED,
    YELLOW,
    GREEN
  }

  private abstract static class CountingSupplier<E> implements Supplier<E>, Serializable {
    int count;

    abstract E getImpl();

    assertThat(
      requestAfter.exchangeIndex == 0 ||
        server.requestCount == 3 &&
        server.takeRequest().exchangeIndex == 0,
    ).isTrue()
  }

  internal enum class WriteKind {
    BYTE_BY_BYTE,
    SMALL_BUFFERS,
    LARGE_BUFFERS,
  }

  @Test
  fun chunkedUpload_byteByByte() {
    doUpload(TransferKind.CHUNKED, WriteKind.BYTE_BY_BYTE)
  }

   * long[])}.
   *
   * @since 2.0
   */
  public static Comparator<long[]> lexicographicalComparator() {
    return LexicographicalComparator.INSTANCE;
  }

  private enum LexicographicalComparator implements Comparator<long[]> {
    INSTANCE;

    @Override
    public int compare(long[] left, long[] right) {
      int minLength = Math.min(left.length, right.length);

  }

  boolean usesKeyReferences() {
    return keyStrength != Strength.STRONG;
  }

  boolean usesValueReferences() {
    return valueStrength != Strength.STRONG;
  }

  enum Strength {
    /*
     * TODO(kevinb): If we strongly reference the value and aren't loading, we needn't wrap the
     * value. This could save ~8 bytes per entry.
     */

    STRONG {
      @Override

    try {
      return state.closeables.whenClosedCountDown();
    } finally {
      reachabilityFence(this);
    }
  }

  /** The status of a {@link CloseableList}. */
  enum Status {
    /** The {@link CloseableList} has not been subsumed or closed. */
    OPEN,

    /**
     * The {@link CloseableList} has been subsumed into another. It may not be closed or subsumed