* already a {@code FluentIterable}.
   *
   * <p><b>{@code Stream} equivalent:</b> {@link Collection#stream} if {@code iterable} is a {@link
   * Collection}; {@link Streams#stream(Iterable)} otherwise.
   */
  public static <E extends @Nullable Object> FluentIterable<E> from(Iterable<E> iterable) {
    return (iterable instanceof FluentIterable)
        ? (FluentIterable<E>) iterable

    FluentIterable<TimeUnit> unused = FluentIterable.from(TimeUnit.values()).append(SECONDS);
  }

  public void testFromArrayAndIteratorRemove() {
    FluentIterable<TimeUnit> units = FluentIterable.from(TimeUnit.values());
    assertThrows(UnsupportedOperationException.class, () -> removeIf(units, equalTo(SECONDS)));
  }

  public void testFrom() {
    assertEquals(
        ImmutableList.of(1, 2, 3, 4),

    checkNotNull(annotationType);
    return FluentIterable.from(annotations).filter(annotationType).first().orNull();
  }

  /**
   * @since 18.0
   */
  @Override
  public <A extends Annotation> A[] getDeclaredAnnotationsByType(Class<A> annotationType) {
    @Nullable A[] result =
        FluentIterable.from(annotations).filter(annotationType).toArray(annotationType);

 * b/310253115.
 */
@NullUnmarked
public class WriteReplaceOverridesTest extends TestCase {
  private static final ImmutableSet<String> GUAVA_PACKAGES =
      FluentIterable.of(
              "base",
              "cache",
              "collect",
              "escape",
              "eventbus",
              "graph",
              "hash",
              "html",

    assertThat(onlyPresent).containsExactly(2);
  }

  private static Optional<Integer> getSomeOptionalInt() {
    return Optional.of(1);
  }

  private static FluentIterable<? extends Number> getSomeNumbers() {
    return FluentIterable.from(ImmutableList.<Number>of());
  }

  /*
   * The following tests demonstrate the shortcomings of or() and test that the casting workaround

  public static <E> Iterable<E> unmodifiableIterable(ImmutableCollection<E> iterable) {
    return checkNotNull(iterable);
  }

  private static final class UnmodifiableIterable<T extends @Nullable Object>
      extends FluentIterable<T> {
    private final Iterable<? extends T> iterable;

    private UnmodifiableIterable(Iterable<? extends T> iterable) {
      this.iterable = iterable;
    }

    @Override

  public static <E> Iterable<E> unmodifiableIterable(ImmutableCollection<E> iterable) {
    return checkNotNull(iterable);
  }

  private static final class UnmodifiableIterable<T extends @Nullable Object>
      extends FluentIterable<T> {
    private final Iterable<? extends T> iterable;

    private UnmodifiableIterable(Iterable<? extends T> iterable) {
      this.iterable = iterable;
    }

    @Override

 * b/310253115.
 */
@NullUnmarked
public class WriteReplaceOverridesTest extends TestCase {
  private static final ImmutableSet<String> GUAVA_PACKAGES =
      FluentIterable.of(
              "base",
              "cache",
              "collect",
              "escape",
              "eventbus",
              "graph",
              "hash",
              "html",

   *
   * {@snippet :
   * Optional<Integer> optionalInt = getSomeOptionalInt();
   * Number value = optionalInt.or(0.5); // error
   *
   * FluentIterable<? extends Number> numbers = getSomeNumbers();
   * Optional<? extends Number> first = numbers.first();
   * Number value = first.or(0.5); // error
   * }
   *

   *
   * <p><b>Note:</b> if mutability is not required and the elements are non-null, use {@link
   * ImmutableList#copyOf(Iterable)} instead. (Or, change {@code elements} to be a {@link
   * FluentIterable} and call {@code elements.toList()}.)
   *
   * <p><b>Note:</b> if {@code elements} is a {@link Collection}, you don't need this method. Use