* }
   * }</pre>
   *
   * ... can be replaced with:
   *
   * <pre>{@code
   * possibleFoo.ifPresent(foo -> doSomethingWith(foo));
   * }</pre>
   *
   * <p><b>Java 9 users:</b> some use cases can be written with calls to {@code optional.stream()}.
   *
   * @since 11.0
   */
  public abstract Set<T> asSet();

  /**

     * best we can do (since logging may overflow the stack) is to let the error propagate. Because
     * it is an Error, it won't be caught and logged by AbstractFuture.executeListener. Instead, it
     * can propagate through many layers of AbstractTransformFuture up to the root call to set().
     *
     * https://github.com/google/guava/issues/2254
     *
     * Other kinds of Errors are possible:
     *

    executor.execute(task);
    assertEquals(1, numCalls.get());
  }

  /*
   * Under Android, MyError propagates up and fails the test?
   *
   * TODO(b/218700094): Does this matter to prod users, or is it just a feature of our testing
   * environment? If the latter, maybe write a custom Executor that avoids failing the test when it
   * sees an Error?
   */
  @AndroidIncompatible

 * #createStarted(Ticker)} to supply a fake or mock ticker. This allows you to simulate any valid
 * behavior of the stopwatch.
 *
 * <p><b>Note:</b> This class is not thread-safe.
 *
 * <p><b>Warning for Android users:</b> a stopwatch with default behavior may not continue to keep
 * time while the device is asleep. Instead, create one like this:
 *
 * <pre>{@code
 * Stopwatch.createStarted(
 *      new Ticker() {

  }

  @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
  }

        // getDeclaredField to throw a NoSuchFieldException when the field is definitely there.
        // For these users fallback to a suboptimal implementation, based on synchronized. This will
        // be a definite performance hit to those users.
        thrownAtomicReferenceFieldUpdaterFailure = atomicReferenceFieldUpdaterFailure;
        helper = new SynchronizedHelper();
      }
    }

   * throws an {@code IllegalStateException}.)
   *
   * @since 33.2.0 (available since 21.0 in guava-jre)
   */
  @SuppressWarnings({"AndroidJdkLibsChecker", "Java7ApiChecker"})
  @IgnoreJRERequirement // Users will use this only if they're already using streams.
  @Beta // TODO: b/288085449 - Remove.
  public static <T extends @Nullable Object, K, V>
      Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(

   *
   * @since 33.2.0 (available since 23.1 in guava-jre)
   */
  @SuppressWarnings({"AndroidJdkLibsChecker", "Java7ApiChecker"})
  @IgnoreJRERequirement // Users will use this only if they're already using streams.
  @Beta // TODO: b/288085449 - Remove.
  public static <T extends @Nullable Object, K extends Comparable<? super K>, V>

   * should speed up for a while, to take advantage of these resources. This is important when the
   * rate is applied to networking (limiting bandwidth), where past underutilization typically
   * translates to "almost empty buffers", which can be filled immediately.
   *
   * On the other hand, past underutilization could mean that "the server responsible for handling
   * the request has become less ready for future requests", i.e. its caches become stale, and

   * accomplished with {@link Optional#or(Object) first.or(second)}. That approach also allows for
   * lazy evaluation of the fallback instance, using {@link Optional#or(Supplier)
   * first.or(supplier)}.
   *
   * <p><b>Java 9 users:</b> use {@code java.util.Objects.requireNonNullElse(first, second)}
   * instead.
   *
   * @return {@code first} if it is non-null; otherwise {@code second} if it is non-null