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;
022
023import java.util.Collection;
024import java.util.Iterator;
025import java.util.Map;
026import java.util.Set;
027
028import 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
059public 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(@Nullable Object key) {
090    return delegate().containsKey(key);
091  }
092
093  @Override
094  public boolean containsValue(@Nullable Object value) {
095    return delegate().containsValue(value);
096  }
097
098  @Override
099  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}