* @since 33.1.0
   */
  @Beta // only until we're confident that Java 8+ APIs are safe for our Android users
  @J2ktIncompatible
  @GwtIncompatible // java.time.Duration
  @SuppressWarnings("Java7ApiChecker") // no more dangerous that wherever the user got the Duration
  @IgnoreJRERequirement
  public static <T extends @Nullable Object> Supplier<T> memoizeWithExpiration(

   *   <li>{@code false} in all other situations.
   * </ul>
   *
   * <p>This assumes that any non-null objects passed to this function conform to the {@code
   * equals()} contract.
   *
   * <p><b>Java 7+ users:</b> This method should be treated as deprecated; use {@link
   * java.util.Objects#equals} instead.
   */
  public static boolean equal(@CheckForNull Object a, @CheckForNull Object b) {

   *   <li>{@code false} in all other situations.
   * </ul>
   *
   * <p>This assumes that any non-null objects passed to this function conform to the {@code
   * equals()} contract.
   *
   * <p><b>Java 7+ users:</b> This method should be treated as deprecated; use {@link
   * java.util.Objects#equals} instead.
   */
  public static boolean equal(@CheckForNull Object a, @CheckForNull Object b) {

 *       look for any annotation named, e.g., "GwtIncompatible," regardless of package.
 *   <li>An annotation named just "Suppress" might suggest to users that the test is suppressed
 *       under all environments. We could fight this by fully qualifying the annotation, but the
 *       result will be verbose and attention-grabbing.

import com.google.common.annotations.GwtCompatible;

/**
 * A time source; returns a time value representing the number of nanoseconds elapsed since some
 * fixed but arbitrary point in time. Note that most users should use {@link Stopwatch} instead of
 * interacting with this class directly.
 *
 * <p><b>Warning:</b> this interface can only be used to measure elapsed time, not wall time.
 *
 * @author Kevin Bourrillion

   * already been re-added.
   */
  // Technically should accept RemovalNotification<? extends K, ? extends V>, but because
  // RemovalNotification is guaranteed covariant, let's make users' lives simpler.
  void onRemoval(RemovalNotification<K, V> notification);

   *
   * <p><b>Warning to users of Java 8+:</b> do not call any of the new <i>default methods</i> that
   * have been newly added to {@link ConcurrentMap}! These are marked with "Since: 1.8" in the
   * {@code ConcurrentMap} documentation. They will not function correctly and it is impossible for
   * Guava to fix them until Guava is ready to <i>require</i> Java 8 for all users.
   */
  ConcurrentMap<K, V> asMap();

  /**

      // For these users fallback to a suboptimal implementation, based on synchronized. This will
      // be a definite performance hit to those users.
      thrownReflectionFailure = reflectionFailure;
      helper = new SynchronizedAtomicHelper();
    }
    ATOMIC_HELPER = helper;
    // Log after all static init is finished; if an installed logger uses any Futures methods, it

        Be aware, though: most feature requests are not accepted, even if they're suggested by
        a full-time Guava team member. [Feedback](https://stackoverflow.com/a/4543114) from our
        users indicates that they really appreciate Guava's high power-to-weight ratio. It's
        important to us to keep Guava as easy to use and understand as we can. That means boiling

  }

  @SuppressWarnings("unused") // compilation test
  public void testSampleCodeFine2() {
    FluentIterable<? extends Number> numbers = getSomeNumbers();

    // Sadly, the following is what users will have to do in some circumstances.

    @SuppressWarnings("unchecked") // safe covariant cast
    Optional<Number> first = (Optional<Number>) numbers.first();
    Number value = first.or(0.5); // fine
  }