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