* arrays. Like {@code Joiner}, it is thread-safe and immutable.
   *
   * <p>In addition to operating on {@code Map} instances, {@code MapJoiner} can operate on {@code
   * Multimap} entries in two distinct modes:
   *
   * <ul>
   *   <li>To output a separate entry for each key-value pair, pass {@code multimap.entries()} to a
   *       {@code MapJoiner} method that accepts entries as input, and receive output of the form

 *
 * <p>A non-null {@code Optional<T>} reference can be used as a replacement for a nullable {@code T}
 * reference. It allows you to represent "a {@code T} that must be present" and a "a {@code T} that
 * might be absent" as two distinct types in your program, which can aid clarity.
 *
 * <p>Some uses of this class include
 *
 * <ul>
 *   <li>As a method return type, as an alternative to returning {@code null} to indicate that no

   * It will never change, even if the maps change at a later time.
   *
   * <p>Since this method uses {@code TreeMap} instances internally, the keys of the right map must
   * all compare as distinct according to the comparator of the left map.
   *
   * <p><b>Note:</b>If you only need to know whether two sorted maps have the same mappings, call
   * {@code left.equals(right)} instead of this method.
   *

   *
   * <p><b>Warning: do not depend</b> on the behavior of this method.
   *
   * <p>Historically, {@code Equivalence} instances in this library have implemented this method to
   * recognize certain cases where distinct {@code Equivalence} instances would in fact behave
   * identically. However, as code migrates to {@code java.util.function}, that behavior will
   * disappear. It is best not to depend on it.
   */
  @Override

 *   <li><a href="https://dagger.dev/producers.html">Dagger Producers</a>
 * </ul>
 *
 * <p>If you do chain your operations manually, you may want to use {@link FluentFuture}.
 *
 * @author Kevin Bourrillion
 * @author Nishant Thakkar
 * @author Sven Mawson
 * @since 1.0
 */
@GwtCompatible
public final class Futures extends GwtFuturesCatchingSpecialization {

  // A note on memory visibility.

  /**
   * Null ('\0'): The all-zeros character which may serve to accomplish time fill and media fill.
   * Normally used as a C string terminator.
   *
   * <p>Although RFC 20 names this as "Null", note that it is distinct from the C/C++ "NULL"
   * pointer.
   *
   * @since 8.0
   */
  public static final byte NUL = 0;

  /**
   * Start of Heading: A communication control character used at the beginning of a sequence of

    @GwtIncompatible // Spliterator
    Spliterator<Entry<K, V>> entrySpliterator() {
      return Spliterators.spliterator(
          entryIterator(),
          size(),
          Spliterator.DISTINCT | Spliterator.NONNULL | Spliterator.IMMUTABLE | Spliterator.ORDERED);
    }

    @Override
    ImmutableSet<K> createKeySet() {
      return new ImmutableMapKeySet<>(this);
    }

    @Override

   * inequality.
   */
  protected final <T> void setDefault(Class<T> type, T value) {
    tester.setDefault(type, value);
  }

  /**
   * Sets two distinct values for {@code type}. These values can be used for both null pointer
   * testing and equals testing.
   *
   * @since 17.0
   */
  protected final <T> void setDistinctValues(Class<T> type, T value1, T value2) {

      } else {
        return false;
      }
    }

    @Override
    public int hashCode() {
      return m.hashCode();
    }
  }

  // Test that we should get a distinct parameter error when doing equals test.
  static class ConstructorParameterWithOptionalNotInstantiable {
    public ConstructorParameterWithOptionalNotInstantiable(Optional<NotInstantiable> x) {
      checkNotNull(x);

    }

    @Override
    public Multiset<K> create(Object... elements) {
      /*
       * This is nasty and complicated, but it's the only way to make sure keys get mapped to enough
       * distinct values.
       */
      Entry<?, ?>[] entries = new Entry<?, ?>[elements.length];
      Map<K, Iterator<V>> valueIterators = new HashMap<>();
      for (int i = 0; i < elements.length; i++) {