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.Set;
026import org.checkerframework.checker.nullness.compatqual.NullableDecl;
027
028/**
029 * A multiset which forwards all its method calls to another multiset. Subclasses should override
030 * one or more methods to modify the behavior of the backing multiset as desired per the <a
031 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
032 *
033 * <p><b>Warning:</b> The methods of {@code ForwardingMultiset} forward <b>indiscriminately</b> to
034 * the methods of the delegate. For example, overriding {@link #add(Object, int)} alone <b>will
035 * not</b> change the behavior of {@link #add(Object)}, which can lead to unexpected behavior. In
036 * this case, you should override {@code add(Object)} as well, either providing your own
037 * implementation, or delegating to the provided {@code standardAdd} method.
038 *
039 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
040 * default} methods. Instead, it inherits their default implementations. When those implementations
041 * invoke methods, they invoke methods on the {@code ForwardingMultiset}.
042 *
043 * <p>The {@code standard} methods and any collection views they return are not guaranteed to be
044 * thread-safe, even when all of the methods that they depend on are thread-safe.
045 *
046 * @author Kevin Bourrillion
047 * @author Louis Wasserman
048 * @since 2.0
049 */
050@GwtCompatible
051public abstract class ForwardingMultiset<E> extends ForwardingCollection<E> implements Multiset<E> {
052
053  /** Constructor for use by subclasses. */
054  protected ForwardingMultiset() {}
055
056  @Override
057  protected abstract Multiset<E> delegate();
058
059  @Override
060  public int count(Object element) {
061    return delegate().count(element);
062  }
063
064  @CanIgnoreReturnValue
065  @Override
066  public int add(E element, int occurrences) {
067    return delegate().add(element, occurrences);
068  }
069
070  @CanIgnoreReturnValue
071  @Override
072  public int remove(Object element, int occurrences) {
073    return delegate().remove(element, occurrences);
074  }
075
076  @Override
077  public Set<E> elementSet() {
078    return delegate().elementSet();
079  }
080
081  @Override
082  public Set<Entry<E>> entrySet() {
083    return delegate().entrySet();
084  }
085
086  @Override
087  public boolean equals(@NullableDecl Object object) {
088    return object == this || delegate().equals(object);
089  }
090
091  @Override
092  public int hashCode() {
093    return delegate().hashCode();
094  }
095
096  @CanIgnoreReturnValue
097  @Override
098  public int setCount(E element, int count) {
099    return delegate().setCount(element, count);
100  }
101
102  @CanIgnoreReturnValue
103  @Override
104  public boolean setCount(E element, int oldCount, int newCount) {
105    return delegate().setCount(element, oldCount, newCount);
106  }
107
108  /**
109   * A sensible definition of {@link #contains} in terms of {@link #count}. If you override {@link
110   * #count}, you may wish to override {@link #contains} to forward to this implementation.
111   *
112   * @since 7.0
113   */
114  @Override
115  protected boolean standardContains(@NullableDecl Object object) {
116    return count(object) > 0;
117  }
118
119  /**
120   * A sensible definition of {@link #clear} in terms of the {@code iterator} method of {@link
121   * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #clear} to
122   * forward to this implementation.
123   *
124   * @since 7.0
125   */
126  @Override
127  protected void standardClear() {
128    Iterators.clear(entrySet().iterator());
129  }
130
131  /**
132   * A sensible, albeit inefficient, definition of {@link #count} in terms of {@link #entrySet}. If
133   * you override {@link #entrySet}, you may wish to override {@link #count} to forward to this
134   * implementation.
135   *
136   * @since 7.0
137   */
138  @Beta
139  protected int standardCount(@NullableDecl Object object) {
140    for (Entry<?> entry : this.entrySet()) {
141      if (Objects.equal(entry.getElement(), object)) {
142        return entry.getCount();
143      }
144    }
145    return 0;
146  }
147
148  /**
149   * A sensible definition of {@link #add(Object)} in terms of {@link #add(Object, int)}. If you
150   * override {@link #add(Object, int)}, you may wish to override {@link #add(Object)} to forward to
151   * this implementation.
152   *
153   * @since 7.0
154   */
155  protected boolean standardAdd(E element) {
156    add(element, 1);
157    return true;
158  }
159
160  /**
161   * A sensible definition of {@link #addAll(Collection)} in terms of {@link #add(Object)} and
162   * {@link #add(Object, int)}. If you override either of these methods, you may wish to override
163   * {@link #addAll(Collection)} to forward to this implementation.
164   *
165   * @since 7.0
166   */
167  @Beta
168  @Override
169  protected boolean standardAddAll(Collection<? extends E> elementsToAdd) {
170    return Multisets.addAllImpl(this, elementsToAdd);
171  }
172
173  /**
174   * A sensible definition of {@link #remove(Object)} in terms of {@link #remove(Object, int)}. If
175   * you override {@link #remove(Object, int)}, you may wish to override {@link #remove(Object)} to
176   * forward to this implementation.
177   *
178   * @since 7.0
179   */
180  @Override
181  protected boolean standardRemove(Object element) {
182    return remove(element, 1) > 0;
183  }
184
185  /**
186   * A sensible definition of {@link #removeAll} in terms of the {@code removeAll} method of {@link
187   * #elementSet}. If you override {@link #elementSet}, you may wish to override {@link #removeAll}
188   * to forward to this implementation.
189   *
190   * @since 7.0
191   */
192  @Override
193  protected boolean standardRemoveAll(Collection<?> elementsToRemove) {
194    return Multisets.removeAllImpl(this, elementsToRemove);
195  }
196
197  /**
198   * A sensible definition of {@link #retainAll} in terms of the {@code retainAll} method of {@link
199   * #elementSet}. If you override {@link #elementSet}, you may wish to override {@link #retainAll}
200   * to forward to this implementation.
201   *
202   * @since 7.0
203   */
204  @Override
205  protected boolean standardRetainAll(Collection<?> elementsToRetain) {
206    return Multisets.retainAllImpl(this, elementsToRetain);
207  }
208
209  /**
210   * A sensible definition of {@link #setCount(Object, int)} in terms of {@link #count(Object)},
211   * {@link #add(Object, int)}, and {@link #remove(Object, int)}. {@link #entrySet()}. If you
212   * override any of these methods, you may wish to override {@link #setCount(Object, int)} to
213   * forward to this implementation.
214   *
215   * @since 7.0
216   */
217  protected int standardSetCount(E element, int count) {
218    return Multisets.setCountImpl(this, element, count);
219  }
220
221  /**
222   * A sensible definition of {@link #setCount(Object, int, int)} in terms of {@link #count(Object)}
223   * and {@link #setCount(Object, int)}. If you override either of these methods, you may wish to
224   * override {@link #setCount(Object, int, int)} to forward to this implementation.
225   *
226   * @since 7.0
227   */
228  protected boolean standardSetCount(E element, int oldCount, int newCount) {
229    return Multisets.setCountImpl(this, element, oldCount, newCount);
230  }
231
232  /**
233   * A sensible implementation of {@link Multiset#elementSet} in terms of the following methods:
234   * {@link ForwardingMultiset#clear}, {@link ForwardingMultiset#contains}, {@link
235   * ForwardingMultiset#containsAll}, {@link ForwardingMultiset#count}, {@link
236   * ForwardingMultiset#isEmpty}, the {@link Set#size} and {@link Set#iterator} methods of {@link
237   * ForwardingMultiset#entrySet}, and {@link ForwardingMultiset#remove(Object, int)}. In many
238   * situations, you may wish to override {@link ForwardingMultiset#elementSet} to forward to this
239   * implementation or a subclass thereof.
240   *
241   * @since 10.0
242   */
243  @Beta
244  protected class StandardElementSet extends Multisets.ElementSet<E> {
245    /** Constructor for use by subclasses. */
246    public StandardElementSet() {}
247
248    @Override
249    Multiset<E> multiset() {
250      return ForwardingMultiset.this;
251    }
252  }
253
254  /**
255   * A sensible definition of {@link #iterator} in terms of {@link #entrySet} and {@link
256   * #remove(Object)}. If you override either of these methods, you may wish to override {@link
257   * #iterator} to forward to this implementation.
258   *
259   * @since 7.0
260   */
261  protected Iterator<E> standardIterator() {
262    return Multisets.iteratorImpl(this);
263  }
264
265  /**
266   * A sensible, albeit inefficient, definition of {@link #size} in terms of {@link #entrySet}. If
267   * you override {@link #entrySet}, you may wish to override {@link #size} to forward to this
268   * implementation.
269   *
270   * @since 7.0
271   */
272  protected int standardSize() {
273    return Multisets.sizeImpl(this);
274  }
275
276  /**
277   * A sensible, albeit inefficient, definition of {@link #equals} in terms of {@code
278   * entrySet().size()} and {@link #count}. If you override either of these methods, you may wish to
279   * override {@link #equals} to forward to this implementation.
280   *
281   * @since 7.0
282   */
283  protected boolean standardEquals(@NullableDecl Object object) {
284    return Multisets.equalsImpl(this, object);
285  }
286
287  /**
288   * A sensible definition of {@link #hashCode} as {@code entrySet().hashCode()} . If you override
289   * {@link #entrySet}, you may wish to override {@link #hashCode} to forward to this
290   * implementation.
291   *
292   * @since 7.0
293   */
294  protected int standardHashCode() {
295    return entrySet().hashCode();
296  }
297
298  /**
299   * A sensible definition of {@link #toString} as {@code entrySet().toString()} . If you override
300   * {@link #entrySet}, you may wish to override {@link #toString} to forward to this
301   * implementation.
302   *
303   * @since 7.0
304   */
305  @Override
306  protected String standardToString() {
307    return entrySet().toString();
308  }
309}