001 /*
002 * Copyright (C) 2007 Google Inc.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package com.google.common.collect;
018
019 import com.google.common.annotations.Beta;
020 import com.google.common.annotations.GwtCompatible;
021 import com.google.common.base.Objects;
022
023 import java.util.Map;
024 import java.util.Map.Entry;
025
026 import javax.annotation.Nullable;
027
028 /**
029 * A map entry which forwards all its method calls to another map entry.
030 * Subclasses should override one or more methods to modify the behavior of the
031 * backing map entry as desired per the <a
032 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
033 *
034 * <p><em>Warning</em>: The methods of {@code ForwardingMapEntry} forward
035 * <em>indiscriminately</em> to the methods of the delegate. For example,
036 * overriding {@link #getValue} alone <em>will not</em> change the behavior of
037 * {@link #equals}, which can lead to unexpected behavior. In this case, you
038 * should override {@code equals} as well, either providing your own
039 * implementation, or delegating to the provided {@code standardEquals} method.
040 *
041 * <p>Each of the {@code standard} methods, where appropriate, use {@link
042 * Objects#equal} to test equality for both keys and values. This may not be
043 * the desired behavior for map implementations that use non-standard notions of
044 * key equality, such as the entry of a {@code SortedMap} whose comparator is
045 * not consistent with {@code equals}.
046 *
047 * <p>The {@code standard} methods are not guaranteed to be thread-safe, even
048 * when all of the methods that they depend on are thread-safe.
049 *
050 * @author Mike Bostock
051 * @author Louis Wasserman
052 * @since 2 (imported from Google Collections Library)
053 */
054 @GwtCompatible
055 public abstract class ForwardingMapEntry<K, V>
056 extends ForwardingObject implements Map.Entry<K, V> {
057 // TODO(user): identify places where thread safety is actually lost
058
059 /** Constructor for use by subclasses. */
060 protected ForwardingMapEntry() {}
061
062 @Override protected abstract Map.Entry<K, V> delegate();
063
064 public K getKey() {
065 return delegate().getKey();
066 }
067
068 public V getValue() {
069 return delegate().getValue();
070 }
071
072 public V setValue(V value) {
073 return delegate().setValue(value);
074 }
075
076 @Override public boolean equals(@Nullable Object object) {
077 return delegate().equals(object);
078 }
079
080 @Override public int hashCode() {
081 return delegate().hashCode();
082 }
083
084 /**
085 * A sensible definition of {@link #equals(Object)} in terms of {@link
086 * #getKey()} and {@link #getValue()}. If you override either of these
087 * methods, you may wish to override {@link #equals(Object)} to forward to
088 * this implementation.
089 *
090 * @since 7
091 */
092 @Beta protected boolean standardEquals(@Nullable Object object) {
093 if (object instanceof Entry) {
094 Entry<?, ?> that = (Entry<?, ?>) object;
095 return Objects.equal(this.getKey(), that.getKey())
096 && Objects.equal(this.getValue(), that.getValue());
097 }
098 return false;
099 }
100
101 /**
102 * A sensible definition of {@link #hashCode()} in terms of {@link #getKey()}
103 * and {@link #getValue()}. If you override either of these methods, you may
104 * wish to override {@link #hashCode()} to forward to this implementation.
105 *
106 * @since 7
107 */
108 @Beta protected int standardHashCode() {
109 K k = getKey();
110 V v = getValue();
111 return ((k == null) ? 0 : k.hashCode()) ^ ((v == null) ? 0 : v.hashCode());
112 }
113
114 /**
115 * A sensible definition of {@link #toString} in terms of {@link
116 * #getKey} and {@link #getValue}. If you override either of these
117 * methods, you may wish to override {@link #equals} to forward to this
118 * implementation.
119 *
120 * @since 7
121 */
122 @Beta protected String standardToString() {
123 return getKey() + "=" + getValue();
124 }
125 }