* class was added for Java 8. The two classes are extremely similar, but incompatible (they cannot
 * share a common supertype). <i>All</i> known differences are listed either here or with the
 * relevant methods below.
 *
 * <ul>
 *   <li>This class is serializable; {@code java.util.Optional} is not.
 *   <li>{@code java.util.Optional} has the additional methods {@code ifPresent}, {@code filter},

      // will be resized. That threshold is ceilingPowerOfTwo(capacity*loadFactor), where
      // loadFactor is 0.75 by default. So with the calculation here we ensure that the
      // threshold is equal to ceilingPowerOfTwo(expectedSize). There is a separate code
      // path when the first operation on the new map is putAll(otherMap). There, prior to

      // will be resized. That threshold is ceilingPowerOfTwo(capacity*loadFactor), where
      // loadFactor is 0.75 by default. So with the calculation here we ensure that the
      // threshold is equal to ceilingPowerOfTwo(expectedSize). There is a separate code
      // path when the first operation on the new map is putAll(otherMap). There, prior to

    assertEquals(a, b);
  }

  @SuppressWarnings("TestExceptionChecker") // see comment below
  public <T> void testVariableTypeTokenNotAllowed() {
    /*
     * We'd use assertThrows here, but that causes no exception to be thrown under Java 8,
     * presumably because the ThrowingRunnable lambda triggers some kind of bug in Java 8's
     * reflection implementation.
     */
    try {

  }

  /*
   * Tests that we workaround GWT bug #3621 (or that it is already fixed).
   *
   * A call to of() with a parameter that is not a plain Object[] (here,
   * Interface[]) creates a RegularImmutableSortedSet backed by an array of that
   * type. Later, RegularImmutableSortedSet.toArray() calls System.arraycopy()

  private static <E extends @Nullable Object> boolean addAllImpl(
      Multiset<E> self, Multiset<? extends E> elements) {
    // It'd be nice if we could specialize for ImmutableMultiset here without also retaining
    // its code when it's not in scope...
    if (elements instanceof AbstractMapBasedMultiset) {
      return addAllImpl(self, (AbstractMapBasedMultiset<? extends E>) elements);

    // exchanging two blocks of memory). This classic text by Gries and Mills mentions several:
    // https://ecommons.cornell.edu/bitstream/handle/1813/6292/81-452.pdf.
    // (1) "Reversal", the one we have here.
    // (2) "Dolphin". If we're rotating an array a of size n by a distance of d, then element a[0]
    //     ends up at a[d], which in turn ends up at a[2d], and so on until we get back to a[0].

   * previously configured separator between each.
   */
  public String join(Iterable<?> parts) {
    // We don't use the same optimization here as in the JRE flavor.
    // TODO: b/381289911 - Evaluate the performance impact of doing so.
    return join(parts.iterator());
  }

  /*

    return stringWriter.toString();
  }

  /**
   * Returns the stack trace of {@code throwable}, possibly providing slower iteration over the full
   * trace but faster iteration over parts of the trace. Here, "slower" and "faster" are defined in
   * comparison to the normal way to access the stack trace, {@link Throwable#getStackTrace()
   * throwable.getStackTrace()}. Note, however, that this method's special implementation is not

    }
  }

  // TODO(fry): Separate logic for consistency between emul and nonemul implementation.
  // TODO(fry): Look into Maps.KeySet and Maps.Values, which can ideally be reused here but are
  // currently only package visible.
  abstract class AbstractCacheSet<T> extends AbstractSet<T> {
    final ConcurrentMap<?, ?> map;

    AbstractCacheSet(ConcurrentMap<?, ?> map) {
      this.map = map;