*/
@DoNotMock("Use Optional.of(value) or Optional.absent()")
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
public abstract class Optional<T> implements Serializable {
  /**
   * Returns an {@code Optional} instance with no contained reference.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this method is equivalent to Java 8's
   * {@code Optional.empty}.
   */
  public static <T> Optional<T> absent() {

 */
@DoNotMock("Use Optional.of(value) or Optional.absent()")
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
public abstract class Optional<T> implements Serializable {
  /**
   * Returns an {@code Optional} instance with no contained reference.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this method is equivalent to Java 8's
   * {@code Optional.empty}.
   */
  public static <T> Optional<T> absent() {

    assertThat(Optional.presentInstances(optionals)).isEmpty();
  }

  public void testPresentInstances_somePresent() {
    List<Optional<String>> optionals =
        ImmutableList.of(Optional.of("a"), Optional.<String>absent(), Optional.of("c"));
    assertThat(Optional.presentInstances(optionals)).containsExactly("a", "c").inOrder();
  }

    assertThat(Optional.presentInstances(optionals)).isEmpty();
  }

  public void testPresentInstances_somePresent() {
    List<Optional<String>> optionals =
        ImmutableList.of(Optional.of("a"), Optional.<String>absent(), Optional.of("c"));
    assertThat(Optional.presentInstances(optionals)).containsExactly("a", "c").inOrder();
  }

  }

  private static final Function<Object, Optional<?>> NULLABLE_TO_OPTIONAL =
      new Function<Object, Optional<?>>() {
        @Override
        public Optional<?> apply(@Nullable Object obj) {
          return Optional.fromNullable(obj);
        }
      };

  private static final Function<Optional<?>, @Nullable Object> OPTIONAL_TO_NULLABLE =
      new Function<Optional<?>, @Nullable Object>() {
        @Override

            </Export-Package>
            <Import-Package>
              com.google.common.util.concurrent.internal,
              javax.annotation;resolution:=optional,
              javax.crypto.*;resolution:=optional,
              sun.misc.*;resolution:=optional
            </Import-Package>
            <Bundle-DocURL>https://github.com/google/guava/</Bundle-DocURL>
          </instructions>
        </configuration>

    assertNotNull(ArbitraryInstances.get(Object.class));
    assertEquals(0, ArbitraryInstances.get(Number.class));
    assertEquals(Charsets.UTF_8, ArbitraryInstances.get(Charset.class));
    assertEquals(Optional.empty(), ArbitraryInstances.get(Optional.class));
    assertEquals(OptionalInt.empty(), ArbitraryInstances.get(OptionalInt.class));
    assertEquals(OptionalLong.empty(), ArbitraryInstances.get(OptionalLong.class));

  }

  private static final Function<Object, Optional<?>> NULLABLE_TO_OPTIONAL =
      new Function<Object, Optional<?>>() {
        @Override
        public Optional<?> apply(@Nullable Object obj) {
          return Optional.fromNullable(obj);
        }
      };

  private static final Function<Optional<?>, @Nullable Object> OPTIONAL_TO_NULLABLE =
      new Function<Optional<?>, @Nullable Object>() {
        @Override

    for (TestEnum constant : TestEnum.values()) {
      Optional<TestEnum> result = Enums.getIfPresent(shadowTestEnum, constant.name());
      assertThat(result).isPresent();
      shadowConstants.add(result.get());
    }
    assertEquals(ImmutableSet.<Object>copyOf(shadowTestEnum.getEnumConstants()), shadowConstants);
    Optional<TestEnum> result = Enums.getIfPresent(shadowTestEnum, "blibby");

import static org.junit.Assert.assertArrayEquals;
import static org.junit.Assert.assertThrows;

import com.google.common.base.Charsets;
import com.google.common.base.Optional;
import com.google.common.collect.ImmutableList;
import com.google.common.hash.HashCode;
import com.google.common.hash.Hashing;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;