001 /*
002 * Copyright (C) 2007 The Guava Authors
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.Collection;
024 import java.util.Iterator;
025 import java.util.Map;
026 import java.util.Set;
027
028 import javax.annotation.Nullable;
029
030 /**
031 * A map which forwards all its method calls to another map. Subclasses should
032 * override one or more methods to modify the behavior of the backing map as
033 * desired per the <a
034 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
035 *
036 * <p><i>Warning:</i> The methods of {@code ForwardingMap} forward
037 * <i>indiscriminately</i> to the methods of the delegate. For example,
038 * overriding {@link #put} alone <i>will not</i> change the behavior of {@link
039 * #putAll}, which can lead to unexpected behavior. In this case, you should
040 * override {@code putAll} as well, either providing your own implementation, or
041 * delegating to the provided {@code standardPutAll} method.
042 *
043 * <p>Each of the {@code standard} methods, where appropriate, use {@link
044 * Objects#equal} to test equality for both keys and values. This may not be
045 * the desired behavior for map implementations that use non-standard notions of
046 * key equality, such as a {@code SortedMap} whose comparator is not consistent
047 * with {@code equals}.
048 *
049 * <p>The {@code standard} methods and the collection views they return are not
050 * guaranteed to be thread-safe, even when all of the methods that they depend
051 * on are thread-safe.
052 *
053 * @author Kevin Bourrillion
054 * @author Jared Levy
055 * @author Louis Wasserman
056 * @since 2.0 (imported from Google Collections Library)
057 */
058 @GwtCompatible
059 public abstract class ForwardingMap<K, V> extends ForwardingObject
060 implements Map<K, V> {
061 // TODO(user): identify places where thread safety is actually lost
062
063 /** Constructor for use by subclasses. */
064 protected ForwardingMap() {}
065
066 @Override protected abstract Map<K, V> delegate();
067
068 @Override
069 public int size() {
070 return delegate().size();
071 }
072
073 @Override
074 public boolean isEmpty() {
075 return delegate().isEmpty();
076 }
077
078 @Override
079 public V remove(Object object) {
080 return delegate().remove(object);
081 }
082
083 @Override
084 public void clear() {
085 delegate().clear();
086 }
087
088 @Override
089 public boolean containsKey(Object key) {
090 return delegate().containsKey(key);
091 }
092
093 @Override
094 public boolean containsValue(Object value) {
095 return delegate().containsValue(value);
096 }
097
098 @Override
099 public V get(Object key) {
100 return delegate().get(key);
101 }
102
103 @Override
104 public V put(K key, V value) {
105 return delegate().put(key, value);
106 }
107
108 @Override
109 public void putAll(Map<? extends K, ? extends V> map) {
110 delegate().putAll(map);
111 }
112
113 @Override
114 public Set<K> keySet() {
115 return delegate().keySet();
116 }
117
118 @Override
119 public Collection<V> values() {
120 return delegate().values();
121 }
122
123 @Override
124 public Set<Entry<K, V>> entrySet() {
125 return delegate().entrySet();
126 }
127
128 @Override public boolean equals(@Nullable Object object) {
129 return object == this || delegate().equals(object);
130 }
131
132 @Override public int hashCode() {
133 return delegate().hashCode();
134 }
135
136 /**
137 * A sensible definition of {@link #putAll(Map)} in terms of {@link
138 * #put(Object, Object)}. If you override {@link #put(Object, Object)}, you
139 * may wish to override {@link #putAll(Map)} to forward to this
140 * implementation.
141 *
142 * @since 7.0
143 */
144 @Beta protected void standardPutAll(Map<? extends K, ? extends V> map) {
145 Maps.putAllImpl(this, map);
146 }
147
148 /**
149 * A sensible, albeit inefficient, definition of {@link #remove} in terms of
150 * the {@code iterator} method of {@link #entrySet}. If you override {@link
151 * #entrySet}, you may wish to override {@link #remove} to forward to this
152 * implementation.
153 *
154 * <p>Alternately, you may wish to override {@link #remove} with {@code
155 * keySet().remove}, assuming that approach would not lead to an infinite
156 * loop.
157 *
158 * @since 7.0
159 */
160 @Beta protected V standardRemove(@Nullable Object key) {
161 Iterator<Entry<K, V>> entryIterator = entrySet().iterator();
162 while (entryIterator.hasNext()) {
163 Entry<K, V> entry = entryIterator.next();
164 if (Objects.equal(entry.getKey(), key)) {
165 V value = entry.getValue();
166 entryIterator.remove();
167 return value;
168 }
169 }
170 return null;
171 }
172
173 /**
174 * A sensible definition of {@link #clear} in terms of the {@code iterator}
175 * method of {@link #entrySet}. In many cases, you may wish to override
176 * {@link #clear} to forward to this implementation.
177 *
178 * @since 7.0
179 */
180 @Beta protected void standardClear() {
181 Iterator<Entry<K, V>> entryIterator = entrySet().iterator();
182 while (entryIterator.hasNext()) {
183 entryIterator.next();
184 entryIterator.remove();
185 }
186 }
187
188 /**
189 * A sensible implementation of {@link Map#keySet} in terms of the following
190 * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsKey},
191 * {@link ForwardingMap#isEmpty}, {@link ForwardingMap#remove}, {@link
192 * ForwardingMap#size}, and the {@link Set#iterator} method of {@link
193 * ForwardingMap#entrySet}. In many cases, you may wish to override {@link
194 * ForwardingMap#keySet} to forward to this implementation or a subclass
195 * thereof.
196 *
197 * @since 10.0
198 */
199 @Beta
200 protected class StandardKeySet extends Maps.KeySet<K, V> {
201 public StandardKeySet() {}
202
203 @Override
204 Map<K, V> map() {
205 return ForwardingMap.this;
206 }
207 }
208
209 /**
210 * A sensible, albeit inefficient, definition of {@link #containsKey} in terms
211 * of the {@code iterator} method of {@link #entrySet}. If you override {@link
212 * #entrySet}, you may wish to override {@link #containsKey} to forward to
213 * this implementation.
214 *
215 * @since 7.0
216 */
217 @Beta protected boolean standardContainsKey(@Nullable Object key) {
218 return Maps.containsKeyImpl(this, key);
219 }
220
221 /**
222 * A sensible implementation of {@link Map#values} in terms of the following
223 * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsValue},
224 * {@link ForwardingMap#isEmpty}, {@link ForwardingMap#size}, and the {@link
225 * Set#iterator} method of {@link ForwardingMap#entrySet}. In many cases, you
226 * may wish to override {@link ForwardingMap#values} to forward to this
227 * implementation or a subclass thereof.
228 *
229 * @since 10.0
230 */
231 @Beta
232 protected class StandardValues extends Maps.Values<K, V> {
233 public StandardValues() {}
234
235 @Override
236 Map<K, V> map() {
237 return ForwardingMap.this;
238 }
239 }
240
241 /**
242 * A sensible definition of {@link #containsValue} in terms of the {@code
243 * iterator} method of {@link #entrySet}. If you override {@link #entrySet},
244 * you may wish to override {@link #containsValue} to forward to this
245 * implementation.
246 *
247 * @since 7.0
248 */
249 @Beta protected boolean standardContainsValue(@Nullable Object value) {
250 return Maps.containsValueImpl(this, value);
251 }
252
253 /**
254 * A sensible implementation of {@link Map#entrySet} in terms of the following
255 * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsKey},
256 * {@link ForwardingMap#get}, {@link ForwardingMap#isEmpty}, {@link
257 * ForwardingMap#remove}, and {@link ForwardingMap#size}. In many cases, you
258 * may wish to override {@link #entrySet} to forward to this implementation
259 * or a subclass thereof.
260 *
261 * @since 10.0
262 */
263 @Beta
264 protected abstract class StandardEntrySet extends Maps.EntrySet<K, V> {
265 public StandardEntrySet() {}
266
267 @Override
268 Map<K, V> map() {
269 return ForwardingMap.this;
270 }
271 }
272
273 /**
274 * A sensible definition of {@link #isEmpty} in terms of the {@code iterator}
275 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
276 * wish to override {@link #isEmpty} to forward to this implementation.
277 *
278 * @since 7.0
279 */
280 @Beta protected boolean standardIsEmpty() {
281 return !entrySet().iterator().hasNext();
282 }
283
284 /**
285 * A sensible definition of {@link #equals} in terms of the {@code equals}
286 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
287 * wish to override {@link #equals} to forward to this implementation.
288 *
289 * @since 7.0
290 */
291 @Beta protected boolean standardEquals(@Nullable Object object) {
292 return Maps.equalsImpl(this, object);
293 }
294
295 /**
296 * A sensible definition of {@link #hashCode} in terms of the {@code iterator}
297 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
298 * wish to override {@link #hashCode} to forward to this implementation.
299 *
300 * @since 7.0
301 */
302 @Beta protected int standardHashCode() {
303 return Sets.hashCodeImpl(entrySet());
304 }
305
306 /**
307 * A sensible definition of {@link #toString} in terms of the {@code iterator}
308 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
309 * wish to override {@link #toString} to forward to this implementation.
310 *
311 * @since 7.0
312 */
313 @Beta protected String standardToString() {
314 return Maps.toStringImpl(this);
315 }
316 }