.build();

  /**
   * type → implementation. Inherently mutable interfaces and abstract classes are mapped to their
   * default implementations and are "new"d upon get().
   */
  private static final ConcurrentMap<Class<?>, Class<?>> implementations = Maps.newConcurrentMap();

  private static <T> void setImplementation(Class<T> type, Class<? extends T> implementation) {

          .build();

  /**
   * type → implementation. Inherently mutable interfaces and abstract classes are mapped to their
   * default implementations and are "new"d upon get().
   */
  private static final ConcurrentMap<Class<?>, Class<?>> implementations = Maps.newConcurrentMap();

  private static <T> void setImplementation(Class<T> type, Class<? extends T> implementation) {

    return LexicographicalComparatorHolder.PureJavaComparator.INSTANCE;
  }

  /**
   * Provides a lexicographical comparator implementation; either a Java implementation or a faster
   * implementation based on {@link Unsafe}.
   *
   * <p>Uses reflection to gracefully fall back to the Java implementation if {@code Unsafe} isn't
   * available.
   */
  @VisibleForTesting
  static class LexicographicalComparatorHolder {

 *
 * <p>This uses the same efficient implementation as {@link Ordering#leastOf(Iterable, int)},
 * offering expected O(n + k log k) performance (worst case O(n log k)) for n calls to {@link
 * #offer} and a call to {@link #topK}, with O(k) memory. In comparison, quickselect has the same
 * asymptotics but requires O(n) memory, and a {@code PriorityQueue} implementation takes O(n log

   * to custom TypeVariable implementations. As a result, we need to make sure our TypeVariable
   * implementation respects symmetry. Moreover, we don't want to reconstruct a native type variable
   * {@code <A>} using our implementation unless some of its bounds have changed in resolution. This
   * avoids creating unequal TypeVariable implementation unnecessarily. When the bounds do change,

  static <V extends @Nullable Object, X extends Exception> V getChecked(
      Future<V> future, Class<X> exceptionClass) throws X {
    return getChecked(bestGetCheckedTypeValidator(), future, exceptionClass);
  }

  /** Implementation of {@link Futures#getChecked(Future, Class)}. */
  @CanIgnoreReturnValue
  @VisibleForTesting
  @ParametricNullness
  static <V extends @Nullable Object, X extends Exception> V getChecked(

    return LexicographicalComparatorHolder.PureJavaComparator.INSTANCE;
  }

  /**
   * Provides a lexicographical comparator implementation; either a Java implementation or a faster
   * implementation based on {@link Unsafe}.
   *
   * <p>Uses reflection to gracefully fall back to the Java implementation if {@code Unsafe} isn't
   * available.
   */
  @VisibleForTesting
  static class LexicographicalComparatorHolder {

 *       worse, and possibly better, than creating a mutable collection and copying it.
 *   <li>Implementations generally do not cache hash codes. If your element or key type has a slow
 *       {@code hashCode} implementation, it should cache it itself.
 * </ul>
 *
 * <h4>Example usage</h4>
 *
 * <pre>{@code
 * class Foo {

      }
      return max(estimatedSize, 0);
    }

    @Override
    public final int characteristics() {
      return characteristics;
    }
  }

  /**
   * Implementation of {@link Stream#flatMap} with an object spliterator output type.
   *
   * <p>To avoid having this type, we could use {@code FlatMapSpliterator} directly. The main

   * ImmutableEnumSet/ImmutableSortedSet, regardless of implementation type. It
   * captures their "logical contents" and they are reconstructed using public
   * static factories. This is necessary to ensure that the existence of a
   * particular implementation type is an implementation detail.
   */
  @J2ktIncompatible // serialization