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 import com.google.common.base.Supplier;
023
024 import java.util.Collection;
025 import java.util.Iterator;
026 import java.util.Map;
027 import java.util.Set;
028
029 import javax.annotation.Nullable;
030
031 /**
032 * A map which forwards all its method calls to another map. Subclasses should
033 * override one or more methods to modify the behavior of the backing map as
034 * desired per the <a
035 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
036 *
037 * <p><em>Warning</em>: The methods of {@code ForwardingMap} forward
038 * <em>indiscriminately</em> to the methods of the delegate. For example,
039 * overriding {@link #put} alone <em>will not</em> change the behavior of {@link
040 * #putAll}, which can lead to unexpected behavior. In this case, you should
041 * override {@code putAll} as well, either providing your own implementation, or
042 * delegating to the provided {@code standardPutAll} method.
043 *
044 * <p>Each of the {@code standard} methods, where appropriate, use {@link
045 * Objects#equal} to test equality for both keys and values. This may not be
046 * the desired behavior for map implementations that use non-standard notions of
047 * key equality, such as a {@code SortedMap} whose comparator is not consistent
048 * with {@code equals}.
049 *
050 * <p>The {@code standard} methods and the collection views they return are not
051 * guaranteed to be thread-safe, even when all of the methods that they depend
052 * on are thread-safe.
053 *
054 * @author Kevin Bourrillion
055 * @author Jared Levy
056 * @author Louis Wasserman
057 * @since 2 (imported from Google Collections Library)
058 */
059 @GwtCompatible
060 public abstract class ForwardingMap<K, V> extends ForwardingObject
061 implements Map<K, V> {
062 // TODO(user): identify places where thread safety is actually lost
063
064 /** Constructor for use by subclasses. */
065 protected ForwardingMap() {}
066
067 @Override protected abstract Map<K, V> delegate();
068
069 public int size() {
070 return delegate().size();
071 }
072
073 public boolean isEmpty() {
074 return delegate().isEmpty();
075 }
076
077 public V remove(Object object) {
078 return delegate().remove(object);
079 }
080
081 public void clear() {
082 delegate().clear();
083 }
084
085 public boolean containsKey(Object key) {
086 return delegate().containsKey(key);
087 }
088
089 public boolean containsValue(Object value) {
090 return delegate().containsValue(value);
091 }
092
093 public V get(Object key) {
094 return delegate().get(key);
095 }
096
097 public V put(K key, V value) {
098 return delegate().put(key, value);
099 }
100
101 public void putAll(Map<? extends K, ? extends V> map) {
102 delegate().putAll(map);
103 }
104
105 public Set<K> keySet() {
106 return delegate().keySet();
107 }
108
109 public Collection<V> values() {
110 return delegate().values();
111 }
112
113 public Set<Entry<K, V>> entrySet() {
114 return delegate().entrySet();
115 }
116
117 @Override public boolean equals(@Nullable Object object) {
118 return object == this || delegate().equals(object);
119 }
120
121 @Override public int hashCode() {
122 return delegate().hashCode();
123 }
124
125 /**
126 * A sensible definition of {@link #putAll(Map)} in terms of {@link
127 * #put(Object, Object)}. If you override {@link #put(Object, Object)}, you
128 * may wish to override {@link #putAll(Map)} to forward to this
129 * implementation.
130 *
131 * @since 7
132 */
133 @Beta protected void standardPutAll(Map<? extends K, ? extends V> map) {
134 Maps.putAllImpl(this, map);
135 }
136
137 /**
138 * A sensible, albeit inefficient, definition of {@link #remove} in terms of
139 * the {@code iterator} method of {@link #entrySet}. If you override {@link
140 * #entrySet}, you may wish to override {@link #remove} to forward to this
141 * implementation.
142 *
143 * <p>Alternately, you may wish to override {@link #remove} with {@code
144 * keySet().remove}, assuming that approach would not lead to an infinite
145 * loop.
146 *
147 * @since 7
148 */
149 @Beta protected V standardRemove(@Nullable Object key) {
150 Iterator<Entry<K, V>> entryIterator = entrySet().iterator();
151 while (entryIterator.hasNext()) {
152 Entry<K, V> entry = entryIterator.next();
153 if (Objects.equal(entry.getKey(), key)) {
154 V value = entry.getValue();
155 entryIterator.remove();
156 return value;
157 }
158 }
159 return null;
160 }
161
162 /**
163 * A sensible definition of {@link #clear} in terms of the {@code iterator}
164 * method of {@link #entrySet}. In many cases, you may wish to override
165 * {@link #clear} to forward to this implementation.
166 *
167 * @since 7
168 */
169 @Beta protected void standardClear() {
170 Iterator<Entry<K, V>> entryIterator = entrySet().iterator();
171 while (entryIterator.hasNext()) {
172 entryIterator.next();
173 entryIterator.remove();
174 }
175 }
176
177 /**
178 * A sensible definition of {@link #keySet} in terms of the following methods:
179 * {@link #clear}, {@link #containsKey}, {@link #isEmpty}, {@link #remove},
180 * {@link #size}, and the {@code iterator} method of {@link #entrySet}. In
181 * many cases, you may wish to override {@link #keySet} to forward to this
182 * implementation.
183 *
184 * @since 7
185 */
186 @Beta protected Set<K> standardKeySet() {
187 return Maps.keySetImpl(this);
188 }
189
190 /**
191 * A sensible, albeit inefficient, definition of {@link #containsKey} in terms
192 * of the {@code iterator} method of {@link #entrySet}. If you override {@link
193 * #entrySet}, you may wish to override {@link #containsKey} to forward to
194 * this implementation.
195 *
196 * @since 7
197 */
198 @Beta protected boolean standardContainsKey(@Nullable Object key) {
199 return Maps.containsKeyImpl(this, key);
200 }
201
202 /**
203 * A sensible definition of {@link #values} in terms of the following methods:
204 * {@link #clear}, {@link #containsValue}, {@link #isEmpty}, {@link #size},
205 * and the {@code iterator} method of {@link #entrySet}. In many cases, you
206 * may wish to override {@link #values} to forward to this implementation.
207 *
208 * @since 7
209 */
210 @Beta protected Collection<V> standardValues() {
211 return Maps.valuesImpl(this);
212 }
213
214 /**
215 * A sensible definition of {@link #containsValue} in terms of the {@code
216 * iterator} method of {@link #entrySet}. If you override {@link #entrySet},
217 * you may wish to override {@link #containsValue} to forward to this
218 * implementation.
219 *
220 * @since 7
221 */
222 @Beta protected boolean standardContainsValue(@Nullable Object value) {
223 return Maps.containsValueImpl(this, value);
224 }
225
226 /**
227 * A sensible definition of {@link #entrySet} in terms of the specified {@code
228 * Supplier}, which is used to generate iterators over the entry set, and in
229 * terms of the following methods: {@link #clear}, {@link #containsKey},
230 * {@link #get}, {@link #isEmpty}, {@link #remove}, and {@link #size}. In many
231 * cases, you may wish to override {@link #entrySet} to forward to this
232 * implementation.
233 *
234 * @param entryIteratorSupplier A creator for iterators over the entry set.
235 * Each call to {@code get} must return an iterator that will
236 * traverse the entire entry set.
237 *
238 * @since 7
239 */
240 @Beta protected Set<Entry<K, V>> standardEntrySet(
241 Supplier<Iterator<Entry<K, V>>> entryIteratorSupplier) {
242 return Maps.entrySetImpl(this, entryIteratorSupplier);
243 }
244
245 /**
246 * A sensible definition of {@link #isEmpty} in terms of the {@code iterator}
247 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
248 * wish to override {@link #isEmpty} to forward to this implementation.
249 *
250 * @since 7
251 */
252 @Beta protected boolean standardIsEmpty() {
253 return !entrySet().iterator().hasNext();
254 }
255
256 /**
257 * A sensible definition of {@link #equals} in terms of the {@code equals}
258 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
259 * wish to override {@link #equals} to forward to this implementation.
260 *
261 * @since 7
262 */
263 @Beta protected boolean standardEquals(@Nullable Object object) {
264 return Maps.equalsImpl(this, object);
265 }
266
267 /**
268 * A sensible definition of {@link #hashCode} in terms of the {@code iterator}
269 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
270 * wish to override {@link #hashCode} to forward to this implementation.
271 *
272 * @since 7
273 */
274 @Beta protected int standardHashCode() {
275 return Sets.hashCodeImpl(entrySet());
276 }
277
278 /**
279 * A sensible definition of {@link #toString} in terms of the {@code iterator}
280 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
281 * wish to override {@link #toString} to forward to this implementation.
282 *
283 * @since 7
284 */
285 @Beta protected String standardToString() {
286 return Maps.toStringImpl(this);
287 }
288 }