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
017package com.google.common.collect;
018
019import com.google.common.annotations.Beta;
020import com.google.common.annotations.GwtCompatible;
021import com.google.common.base.Objects;
022import com.google.common.base.Supplier;
023
024import java.util.Collection;
025import java.util.Iterator;
026import java.util.Map;
027import java.util.Set;
028
029import 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
060public 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  @Override
070  public int size() {
071    return delegate().size();
072  }
073
074  @Override
075  public boolean isEmpty() {
076    return delegate().isEmpty();
077  }
078
079  @Override
080  public V remove(Object object) {
081    return delegate().remove(object);
082  }
083
084  @Override
085  public void clear() {
086    delegate().clear();
087  }
088
089  @Override
090  public boolean containsKey(Object key) {
091    return delegate().containsKey(key);
092  }
093
094  @Override
095  public boolean containsValue(Object value) {
096    return delegate().containsValue(value);
097  }
098
099  @Override
100  public V get(Object key) {
101    return delegate().get(key);
102  }
103
104  @Override
105  public V put(K key, V value) {
106    return delegate().put(key, value);
107  }
108
109  @Override
110  public void putAll(Map<? extends K, ? extends V> map) {
111    delegate().putAll(map);
112  }
113
114  @Override
115  public Set<K> keySet() {
116    return delegate().keySet();
117  }
118
119  @Override
120  public Collection<V> values() {
121    return delegate().values();
122  }
123
124  @Override
125  public Set<Entry<K, V>> entrySet() {
126    return delegate().entrySet();
127  }
128
129  @Override public boolean equals(@Nullable Object object) {
130    return object == this || delegate().equals(object);
131  }
132
133  @Override public int hashCode() {
134    return delegate().hashCode();
135  }
136
137  /**
138   * A sensible definition of {@link #putAll(Map)} in terms of {@link
139   * #put(Object, Object)}. If you override {@link #put(Object, Object)}, you
140   * may wish to override {@link #putAll(Map)} to forward to this
141   * implementation.
142   *
143   * @since 7
144   */
145  @Beta protected void standardPutAll(Map<? extends K, ? extends V> map) {
146    Maps.putAllImpl(this, map);
147  }
148
149  /**
150   * A sensible, albeit inefficient, definition of {@link #remove} in terms of
151   * the {@code iterator} method of {@link #entrySet}. If you override {@link
152   * #entrySet}, you may wish to override {@link #remove} to forward to this
153   * implementation.
154   *
155   * <p>Alternately, you may wish to override {@link #remove} with {@code
156   * keySet().remove}, assuming that approach would not lead to an infinite
157   * loop.
158   *
159   * @since 7
160   */
161  @Beta protected V standardRemove(@Nullable Object key) {
162    Iterator<Entry<K, V>> entryIterator = entrySet().iterator();
163    while (entryIterator.hasNext()) {
164      Entry<K, V> entry = entryIterator.next();
165      if (Objects.equal(entry.getKey(), key)) {
166        V value = entry.getValue();
167        entryIterator.remove();
168        return value;
169      }
170    }
171    return null;
172  }
173
174  /**
175   * A sensible definition of {@link #clear} in terms of the {@code iterator}
176   * method of {@link #entrySet}. In many cases, you may wish to override
177   * {@link #clear} to forward to this implementation.
178   *
179   * @since 7
180   */
181  @Beta protected void standardClear() {
182    Iterator<Entry<K, V>> entryIterator = entrySet().iterator();
183    while (entryIterator.hasNext()) {
184      entryIterator.next();
185      entryIterator.remove();
186    }
187  }
188
189  /**
190   * A sensible definition of {@link #keySet} in terms of the following methods:
191   * {@link #clear}, {@link #containsKey}, {@link #isEmpty}, {@link #remove},
192   * {@link #size}, and the {@code iterator} method of {@link #entrySet}. In
193   * many cases, you may wish to override {@link #keySet} to forward to this
194   * implementation.
195   *
196   * @since 7
197   */
198  @Beta protected Set<K> standardKeySet() {
199    return Maps.keySetImpl(this);
200  }
201
202  /**
203   * A sensible, albeit inefficient, definition of {@link #containsKey} in terms
204   * of the {@code iterator} method of {@link #entrySet}. If you override {@link
205   * #entrySet}, you may wish to override {@link #containsKey} to forward to
206   * this implementation.
207   *
208   * @since 7
209   */
210  @Beta protected boolean standardContainsKey(@Nullable Object key) {
211    return Maps.containsKeyImpl(this, key);
212  }
213
214  /**
215   * A sensible definition of {@link #values} in terms of the following methods:
216   * {@link #clear}, {@link #containsValue}, {@link #isEmpty}, {@link #size},
217   * and the {@code iterator} method of {@link #entrySet}. In many cases, you
218   * may wish to override {@link #values} to forward to this implementation.
219   *
220   * @since 7
221   */
222  @Beta protected Collection<V> standardValues() {
223    return Maps.valuesImpl(this);
224  }
225
226  /**
227   * A sensible definition of {@link #containsValue} in terms of the {@code
228   * iterator} method of {@link #entrySet}. If you override {@link #entrySet},
229   * you may wish to override {@link #containsValue} to forward to this
230   * implementation.
231   *
232   * @since 7
233   */
234  @Beta protected boolean standardContainsValue(@Nullable Object value) {
235    return Maps.containsValueImpl(this, value);
236  }
237
238  /**
239   * A sensible definition of {@link #entrySet} in terms of the specified {@code
240   * Supplier}, which is used to generate iterators over the entry set, and in
241   * terms of the following methods: {@link #clear}, {@link #containsKey},
242   * {@link #get}, {@link #isEmpty}, {@link #remove}, and {@link #size}. In many
243   * cases, you may wish to override {@link #entrySet} to forward to this
244   * implementation.
245   *
246   * @param entryIteratorSupplier A creator for iterators over the entry set.
247   *        Each call to {@code get} must return an iterator that will
248   *        traverse the entire entry set.
249   *
250   * @since 7
251   */
252  @Beta protected Set<Entry<K, V>> standardEntrySet(
253      Supplier<Iterator<Entry<K, V>>> entryIteratorSupplier) {
254    return Maps.entrySetImpl(this, entryIteratorSupplier);
255  }
256
257  /**
258   * A sensible definition of {@link #isEmpty} in terms of the {@code iterator}
259   * method of {@link #entrySet}. If you override {@link #entrySet}, you may
260   * wish to override {@link #isEmpty} to forward to this implementation.
261   *
262   * @since 7
263   */
264  @Beta protected boolean standardIsEmpty() {
265    return !entrySet().iterator().hasNext();
266  }
267
268  /**
269   * A sensible definition of {@link #equals} in terms of the {@code equals}
270   * method of {@link #entrySet}. If you override {@link #entrySet}, you may
271   * wish to override {@link #equals} to forward to this implementation.
272   *
273   * @since 7
274   */
275  @Beta protected boolean standardEquals(@Nullable Object object) {
276    return Maps.equalsImpl(this, object);
277  }
278
279  /**
280   * A sensible definition of {@link #hashCode} in terms of the {@code iterator}
281   * method of {@link #entrySet}. If you override {@link #entrySet}, you may
282   * wish to override {@link #hashCode} to forward to this implementation.
283   *
284   * @since 7
285   */
286  @Beta protected int standardHashCode() {
287    return Sets.hashCodeImpl(entrySet());
288  }
289
290  /**
291   * A sensible definition of {@link #toString} in terms of the {@code iterator}
292   * method of {@link #entrySet}. If you override {@link #entrySet}, you may
293   * wish to override {@link #toString} to forward to this implementation.
294   *
295   * @since 7
296   */
297  @Beta protected String standardToString() {
298    return Maps.toStringImpl(this);
299  }
300}