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
17package com.google.common.collect;
18
19import com.google.common.annotations.Beta;
20import com.google.common.annotations.GwtCompatible;
21import com.google.common.base.Objects;
22
23import java.util.Collection;
24import java.util.Iterator;
25import java.util.Map;
26import java.util.Set;
27
28import 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
59public 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(Object key) {
90    return delegate().containsKey(key);
91  }
92
93  @Override
94  public boolean containsValue(Object value) {
95    return delegate().containsValue(value);
96  }
97
98  @Override
99  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}
317