1 /*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.google.common.collect;
18
19 import com.google.common.annotations.Beta;
20 import com.google.common.annotations.GwtCompatible;
21 import com.google.common.base.Objects;
22
23 import java.util.Collection;
24 import java.util.Iterator;
25 import java.util.Map;
26 import java.util.Set;
27
28 import javax.annotation.Nullable;
29
30 /**
31 * A map which forwards all its method calls to another map. Subclasses should
32 * override one or more methods to modify the behavior of the backing map as
33 * desired per the <a
34 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
35 *
36 * <p><i>Warning:</i> The methods of {@code ForwardingMap} forward
37 * <i>indiscriminately</i> to the methods of the delegate. For example,
38 * overriding {@link #put} alone <i>will not</i> change the behavior of {@link
39 * #putAll}, which can lead to unexpected behavior. In this case, you should
40 * override {@code putAll} as well, either providing your own implementation, or
41 * delegating to the provided {@code standardPutAll} method.
42 *
43 * <p>Each of the {@code standard} methods, where appropriate, use {@link
44 * Objects#equal} to test equality for both keys and values. This may not be
45 * the desired behavior for map implementations that use non-standard notions of
46 * key equality, such as a {@code SortedMap} whose comparator is not consistent
47 * with {@code equals}.
48 *
49 * <p>The {@code standard} methods and the collection views they return are not
50 * guaranteed to be thread-safe, even when all of the methods that they depend
51 * on are thread-safe.
52 *
53 * @author Kevin Bourrillion
54 * @author Jared Levy
55 * @author Louis Wasserman
56 * @since 2.0 (imported from Google Collections Library)
57 */
58 @GwtCompatible
59 public abstract class ForwardingMap<K, V> extends ForwardingObject
60 implements Map<K, V> {
61 // TODO(user): identify places where thread safety is actually lost
62
63 /** Constructor for use by subclasses. */
64 protected ForwardingMap() {}
65
66 @Override protected abstract Map<K, V> delegate();
67
68 @Override
69 public int size() {
70 return delegate().size();
71 }
72
73 @Override
74 public boolean isEmpty() {
75 return delegate().isEmpty();
76 }
77
78 @Override
79 public V remove(Object object) {
80 return delegate().remove(object);
81 }
82
83 @Override
84 public void clear() {
85 delegate().clear();
86 }
87
88 @Override
89 public boolean containsKey(@Nullable Object key) {
90 return delegate().containsKey(key);
91 }
92
93 @Override
94 public boolean containsValue(@Nullable Object value) {
95 return delegate().containsValue(value);
96 }
97
98 @Override
99 public V get(@Nullable 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 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 protected void standardClear() {
181 Iterators.clear(entrySet().iterator());
182 }
183
184 /**
185 * A sensible implementation of {@link Map#keySet} in terms of the following
186 * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsKey},
187 * {@link ForwardingMap#isEmpty}, {@link ForwardingMap#remove}, {@link
188 * ForwardingMap#size}, and the {@link Set#iterator} method of {@link
189 * ForwardingMap#entrySet}. In many cases, you may wish to override {@link
190 * ForwardingMap#keySet} to forward to this implementation or a subclass
191 * thereof.
192 *
193 * @since 10.0
194 */
195 @Beta
196 protected class StandardKeySet extends Maps.KeySet<K, V> {
197 /** Constructor for use by subclasses. */
198 public StandardKeySet() {
199 super(ForwardingMap.this);
200 }
201 }
202
203 /**
204 * A sensible, albeit inefficient, definition of {@link #containsKey} in terms
205 * of the {@code iterator} method of {@link #entrySet}. If you override {@link
206 * #entrySet}, you may wish to override {@link #containsKey} to forward to
207 * this implementation.
208 *
209 * @since 7.0
210 */
211 @Beta protected boolean standardContainsKey(@Nullable Object key) {
212 return Maps.containsKeyImpl(this, key);
213 }
214
215 /**
216 * A sensible implementation of {@link Map#values} in terms of the following
217 * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsValue},
218 * {@link ForwardingMap#isEmpty}, {@link ForwardingMap#size}, and the {@link
219 * Set#iterator} method of {@link ForwardingMap#entrySet}. In many cases, you
220 * may wish to override {@link ForwardingMap#values} to forward to this
221 * implementation or a subclass thereof.
222 *
223 * @since 10.0
224 */
225 @Beta
226 protected class StandardValues extends Maps.Values<K, V> {
227 /** Constructor for use by subclasses. */
228 public StandardValues() {
229 super(ForwardingMap.this);
230 }
231 }
232
233 /**
234 * A sensible definition of {@link #containsValue} in terms of the {@code
235 * iterator} method of {@link #entrySet}. If you override {@link #entrySet},
236 * you may wish to override {@link #containsValue} to forward to this
237 * implementation.
238 *
239 * @since 7.0
240 */
241 protected boolean standardContainsValue(@Nullable Object value) {
242 return Maps.containsValueImpl(this, value);
243 }
244
245 /**
246 * A sensible implementation of {@link Map#entrySet} in terms of the following
247 * methods: {@link ForwardingMap#clear}, {@link ForwardingMap#containsKey},
248 * {@link ForwardingMap#get}, {@link ForwardingMap#isEmpty}, {@link
249 * ForwardingMap#remove}, and {@link ForwardingMap#size}. In many cases, you
250 * may wish to override {@link #entrySet} to forward to this implementation
251 * or a subclass thereof.
252 *
253 * @since 10.0
254 */
255 @Beta
256 protected abstract class StandardEntrySet extends Maps.EntrySet<K, V> {
257 /** Constructor for use by subclasses. */
258 public StandardEntrySet() {}
259
260 @Override
261 Map<K, V> map() {
262 return ForwardingMap.this;
263 }
264 }
265
266 /**
267 * A sensible definition of {@link #isEmpty} in terms of the {@code iterator}
268 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
269 * wish to override {@link #isEmpty} to forward to this implementation.
270 *
271 * @since 7.0
272 */
273 protected boolean standardIsEmpty() {
274 return !entrySet().iterator().hasNext();
275 }
276
277 /**
278 * A sensible definition of {@link #equals} in terms of the {@code equals}
279 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
280 * wish to override {@link #equals} to forward to this implementation.
281 *
282 * @since 7.0
283 */
284 protected boolean standardEquals(@Nullable Object object) {
285 return Maps.equalsImpl(this, object);
286 }
287
288 /**
289 * A sensible definition of {@link #hashCode} in terms of the {@code iterator}
290 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
291 * wish to override {@link #hashCode} to forward to this implementation.
292 *
293 * @since 7.0
294 */
295 protected int standardHashCode() {
296 return Sets.hashCodeImpl(entrySet());
297 }
298
299 /**
300 * A sensible definition of {@link #toString} in terms of the {@code iterator}
301 * method of {@link #entrySet}. If you override {@link #entrySet}, you may
302 * wish to override {@link #toString} to forward to this implementation.
303 *
304 * @since 7.0
305 */
306 protected String standardToString() {
307 return Maps.toStringImpl(this);
308 }
309 }