| /* |
| * Copyright (C) 2011 The Guava Authors |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package com.google.common.base; |
| |
| import static com.google.common.base.Preconditions.checkNotNull; |
| |
| import com.google.common.annotations.GwtCompatible; |
| |
| import java.util.Collections; |
| import java.util.Set; |
| |
| import javax.annotation.Nullable; |
| |
| /** |
| * Implementation of an {@link Optional} not containing a reference. |
| */ |
| @GwtCompatible |
| final class Absent<T> extends Optional<T> { |
| static final Absent<Object> INSTANCE = new Absent<Object>(); |
| |
| @SuppressWarnings("unchecked") // implementation is "fully variant" |
| static <T> Optional<T> withType() { |
| return (Optional<T>) INSTANCE; |
| } |
| |
| private Absent() {} |
| |
| @Override public boolean isPresent() { |
| return false; |
| } |
| |
| @Override public T get() { |
| throw new IllegalStateException("Optional.get() cannot be called on an absent value"); |
| } |
| |
| @Override public T or(T defaultValue) { |
| return checkNotNull(defaultValue, "use Optional.orNull() instead of Optional.or(null)"); |
| } |
| |
| @SuppressWarnings("unchecked") // safe covariant cast |
| @Override public Optional<T> or(Optional<? extends T> secondChoice) { |
| return (Optional<T>) checkNotNull(secondChoice); |
| } |
| |
| @Override public T or(Supplier<? extends T> supplier) { |
| return checkNotNull(supplier.get(), |
| "use Optional.orNull() instead of a Supplier that returns null"); |
| } |
| |
| @Override @Nullable public T orNull() { |
| return null; |
| } |
| |
| @Override public Set<T> asSet() { |
| return Collections.emptySet(); |
| } |
| |
| @Override public <V> Optional<V> transform(Function<? super T, V> function) { |
| checkNotNull(function); |
| return Optional.absent(); |
| } |
| |
| @Override public boolean equals(@Nullable Object object) { |
| return object == this; |
| } |
| |
| @Override public int hashCode() { |
| return 0x598df91c; |
| } |
| |
| @Override public String toString() { |
| return "Optional.absent()"; |
| } |
| |
| private Object readResolve() { |
| return INSTANCE; |
| } |
| |
| private static final long serialVersionUID = 0; |
| } |