135 lines
4.1 KiB
Java
135 lines
4.1 KiB
Java
/*
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* Copyright (C) 2007 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.collect;
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import java.util.Map;
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import java.util.Map.Entry;
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import javax.annotation.Nullable;
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import com.google.common.annotations.Beta;
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import com.google.common.annotations.GwtCompatible;
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import com.google.common.base.Objects;
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/**
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* A map entry which forwards all its method calls to another map entry.
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* Subclasses should override one or more methods to modify the behavior of the
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* backing map entry as desired per the
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* <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator
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* pattern</a>.
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*
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* <p>
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* <i>Warning:</i> The methods of {@code ForwardingMapEntry} forward
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* <i>indiscriminately</i> to the methods of the delegate. For example,
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* overriding {@link #getValue} alone <i>will not</i> change the behavior of
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* {@link #equals}, which can lead to unexpected behavior. In this case, you
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* should override {@code equals} as well, either providing your own
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* implementation, or delegating to the provided {@code standardEquals} method.
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*
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* <p>
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* Each of the {@code standard} methods, where appropriate, use
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* {@link Objects#equal} to test equality for both keys and values. This may not
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* be the desired behavior for map implementations that use non-standard notions
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* of key equality, such as the entry of a {@code SortedMap} whose comparator is
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* not consistent with {@code equals}.
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*
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* <p>
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* The {@code standard} methods are not guaranteed to be thread-safe, even when
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* all of the methods that they depend on are thread-safe.
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*
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* @author Mike Bostock
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* @author Louis Wasserman
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* @since 2.0 (imported from Google Collections Library)
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*/
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@GwtCompatible
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public abstract class ForwardingMapEntry<K, V> extends ForwardingObject implements Map.Entry<K, V> {
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// TODO(user): identify places where thread safety is actually lost
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/** Constructor for use by subclasses. */
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protected ForwardingMapEntry() {
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}
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@Override
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protected abstract Map.Entry<K, V> delegate();
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@Override
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public K getKey() {
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return delegate().getKey();
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}
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@Override
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public V getValue() {
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return delegate().getValue();
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}
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@Override
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public V setValue(V value) {
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return delegate().setValue(value);
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}
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@Override
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public boolean equals(@Nullable Object object) {
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return delegate().equals(object);
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}
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@Override
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public int hashCode() {
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return delegate().hashCode();
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}
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/**
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* A sensible definition of {@link #equals(Object)} in terms of
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* {@link #getKey()} and {@link #getValue()}. If you override either of these
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* methods, you may wish to override {@link #equals(Object)} to forward to this
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* implementation.
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*
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* @since 7.0
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*/
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protected boolean standardEquals(@Nullable Object object) {
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if (object instanceof Entry) {
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Entry<?, ?> that = (Entry<?, ?>) object;
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return Objects.equal(this.getKey(), that.getKey()) && Objects.equal(this.getValue(), that.getValue());
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}
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return false;
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}
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/**
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* A sensible definition of {@link #hashCode()} in terms of {@link #getKey()}
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* and {@link #getValue()}. If you override either of these methods, you may
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* wish to override {@link #hashCode()} to forward to this implementation.
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*
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* @since 7.0
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*/
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protected int standardHashCode() {
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K k = getKey();
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V v = getValue();
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return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode());
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}
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/**
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* A sensible definition of {@link #toString} in terms of {@link #getKey} and
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* {@link #getValue}. If you override either of these methods, you may wish to
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* override {@link #equals} to forward to this implementation.
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*
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* @since 7.0
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*/
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@Beta
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protected String standardToString() {
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return getKey() + "=" + getValue();
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}
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}
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