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.errorprone.annotations.CanIgnoreReturnValue;
023import java.util.Collection;
024import java.util.Iterator;
025import java.util.Map;
026import java.util.Set;
027import org.checkerframework.checker.nullness.qual.Nullable;
028
029/**
030 * A map which forwards all its method calls to another map. Subclasses should override one or more
031 * methods to modify the behavior of the backing map as desired per the <a
032 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
033 *
034 * <p><b>Warning:</b> The methods of {@code ForwardingMap} forward <i>indiscriminately</i> to the
035 * methods of the delegate. For example, overriding {@link #put} alone <i>will not</i> change the
036 * behavior of {@link #putAll}, which can lead to unexpected behavior. In this case, you should
037 * override {@code putAll} as well, either providing your own implementation, or delegating to the
038 * provided {@code standardPutAll} method.
039 *
040 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
041 * default} methods. Instead, it inherits their default implementations. When those implementations
042 * invoke methods, they invoke methods on the {@code ForwardingMap}.
043 *
044 * <p>Each of the {@code standard} methods, where appropriate, use {@link Objects#equal} to test
045 * equality for both keys and values. This may not be the desired behavior for map implementations
046 * that use non-standard notions of key equality, such as a {@code SortedMap} whose comparator is
047 * not consistent with {@code equals}.
048 *
049 * <p>The {@code standard} methods and the collection views they return are not guaranteed to be
050 * thread-safe, even when all of the methods that they depend on are thread-safe.
051 *
052 * @author Kevin Bourrillion
053 * @author Jared Levy
054 * @author Louis Wasserman
055 * @since 2.0
056 */
057@GwtCompatible
058public abstract class ForwardingMap<K, V> extends ForwardingObject implements Map<K, V> {
059  // TODO(lowasser): identify places where thread safety is actually lost
060
061  /** Constructor for use by subclasses. */
062  protected ForwardingMap() {}
063
064  @Override
065  protected abstract Map<K, V> delegate();
066
067  @Override
068  public int size() {
069    return delegate().size();
070  }
071
072  @Override
073  public boolean isEmpty() {
074    return delegate().isEmpty();
075  }
076
077  @CanIgnoreReturnValue
078  @Override
079  public V remove(Object key) {
080    return delegate().remove(key);
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  @CanIgnoreReturnValue
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
130  public boolean equals(@Nullable Object object) {
131    return object == this || delegate().equals(object);
132  }
133
134  @Override
135  public int hashCode() {
136    return delegate().hashCode();
137  }
138
139  /**
140   * A sensible definition of {@link #putAll(Map)} in terms of {@link #put(Object, Object)}. If you
141   * override {@link #put(Object, Object)}, you may wish to override {@link #putAll(Map)} to forward
142   * to this implementation.
143   *
144   * @since 7.0
145   */
146  protected void standardPutAll(Map<? extends K, ? extends V> map) {
147    Maps.putAllImpl(this, map);
148  }
149
150  /**
151   * A sensible, albeit inefficient, definition of {@link #remove} in terms of the {@code iterator}
152   * method of {@link #entrySet}. If you override {@link #entrySet}, you may wish to override {@link
153   * #remove} to forward to this implementation.
154   *
155   * <p>Alternately, you may wish to override {@link #remove} with {@code keySet().remove}, assuming
156   * that approach would not lead to an infinite loop.
157   *
158   * @since 7.0
159   */
160  @Beta
161  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} method of {@link
176   * #entrySet}. In many cases, you may wish to override {@link #clear} to forward to this
177   * implementation.
178   *
179   * @since 7.0
180   */
181  protected void standardClear() {
182    Iterators.clear(entrySet().iterator());
183  }
184
185  /**
186   * A sensible implementation of {@link Map#keySet} in terms of the following methods: {@link
187   * ForwardingMap#clear}, {@link ForwardingMap#containsKey}, {@link ForwardingMap#isEmpty}, {@link
188   * ForwardingMap#remove}, {@link ForwardingMap#size}, and the {@link Set#iterator} method of
189   * {@link ForwardingMap#entrySet}. In many cases, you may wish to override {@link
190   * ForwardingMap#keySet} to forward to this implementation or a subclass thereof.
191   *
192   * @since 10.0
193   */
194  @Beta
195  protected class StandardKeySet extends Maps.KeySet<K, V> {
196    /** Constructor for use by subclasses. */
197    public StandardKeySet() {
198      super(ForwardingMap.this);
199    }
200  }
201
202  /**
203   * A sensible, albeit inefficient, definition of {@link #containsKey} in terms of the {@code
204   * iterator} method of {@link #entrySet}. If you override {@link #entrySet}, you may wish to
205   * override {@link #containsKey} to forward to this implementation.
206   *
207   * @since 7.0
208   */
209  @Beta
210  protected boolean standardContainsKey(@Nullable Object key) {
211    return Maps.containsKeyImpl(this, key);
212  }
213
214  /**
215   * A sensible implementation of {@link Map#values} in terms of the following methods: {@link
216   * ForwardingMap#clear}, {@link ForwardingMap#containsValue}, {@link ForwardingMap#isEmpty},
217   * {@link ForwardingMap#size}, and the {@link Set#iterator} method of {@link
218   * ForwardingMap#entrySet}. In many cases, you may wish to override {@link ForwardingMap#values}
219   * to forward to this implementation or a subclass thereof.
220   *
221   * @since 10.0
222   */
223  @Beta
224  protected class StandardValues extends Maps.Values<K, V> {
225    /** Constructor for use by subclasses. */
226    public StandardValues() {
227      super(ForwardingMap.this);
228    }
229  }
230
231  /**
232   * A sensible definition of {@link #containsValue} in terms of the {@code iterator} method of
233   * {@link #entrySet}. If you override {@link #entrySet}, you may wish to override {@link
234   * #containsValue} to forward to this implementation.
235   *
236   * @since 7.0
237   */
238  protected boolean standardContainsValue(@Nullable Object value) {
239    return Maps.containsValueImpl(this, value);
240  }
241
242  /**
243   * A sensible implementation of {@link Map#entrySet} in terms of the following methods: {@link
244   * ForwardingMap#clear}, {@link ForwardingMap#containsKey}, {@link ForwardingMap#get}, {@link
245   * ForwardingMap#isEmpty}, {@link ForwardingMap#remove}, and {@link ForwardingMap#size}. In many
246   * cases, you may wish to override {@link #entrySet} to forward to this implementation or a
247   * subclass thereof.
248   *
249   * @since 10.0
250   */
251  @Beta
252  protected abstract class StandardEntrySet extends Maps.EntrySet<K, V> {
253    /** Constructor for use by subclasses. */
254    public StandardEntrySet() {}
255
256    @Override
257    Map<K, V> map() {
258      return ForwardingMap.this;
259    }
260  }
261
262  /**
263   * A sensible definition of {@link #isEmpty} in terms of the {@code iterator} method of {@link
264   * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #isEmpty} to
265   * forward to this implementation.
266   *
267   * @since 7.0
268   */
269  protected boolean standardIsEmpty() {
270    return !entrySet().iterator().hasNext();
271  }
272
273  /**
274   * A sensible definition of {@link #equals} in terms of the {@code equals} method of {@link
275   * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #equals} to
276   * forward to this implementation.
277   *
278   * @since 7.0
279   */
280  protected boolean standardEquals(@Nullable Object object) {
281    return Maps.equalsImpl(this, object);
282  }
283
284  /**
285   * A sensible definition of {@link #hashCode} in terms of the {@code iterator} method of {@link
286   * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #hashCode} to
287   * forward to this implementation.
288   *
289   * @since 7.0
290   */
291  protected int standardHashCode() {
292    return Sets.hashCodeImpl(entrySet());
293  }
294
295  /**
296   * A sensible definition of {@link #toString} in terms of the {@code iterator} method of {@link
297   * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #toString} to
298   * forward to this implementation.
299   *
300   * @since 7.0
301   */
302  protected String standardToString() {
303    return Maps.toStringImpl(this);
304  }
305}