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.GwtCompatible;
020import com.google.common.base.Objects;
021import com.google.errorprone.annotations.CanIgnoreReturnValue;
022import java.util.Collection;
023import java.util.Iterator;
024import java.util.Set;
025import javax.annotation.CheckForNull;
026import org.checkerframework.checker.nullness.qual.Nullable;
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
051@ElementTypesAreNonnullByDefault
052public abstract class ForwardingMultiset<E extends @Nullable Object> extends ForwardingCollection<E>
053    implements Multiset<E> {
054
055  /** Constructor for use by subclasses. */
056  protected ForwardingMultiset() {}
057
058  @Override
059  protected abstract Multiset<E> delegate();
060
061  @Override
062  public int count(@CheckForNull Object element) {
063    return delegate().count(element);
064  }
065
066  @CanIgnoreReturnValue
067  @Override
068  public int add(@ParametricNullness E element, int occurrences) {
069    return delegate().add(element, occurrences);
070  }
071
072  @CanIgnoreReturnValue
073  @Override
074  public int remove(@CheckForNull Object element, int occurrences) {
075    return delegate().remove(element, occurrences);
076  }
077
078  @Override
079  public Set<E> elementSet() {
080    return delegate().elementSet();
081  }
082
083  @Override
084  public Set<Entry<E>> entrySet() {
085    return delegate().entrySet();
086  }
087
088  @Override
089  public boolean equals(@CheckForNull Object object) {
090    return object == this || delegate().equals(object);
091  }
092
093  @Override
094  public int hashCode() {
095    return delegate().hashCode();
096  }
097
098  @CanIgnoreReturnValue
099  @Override
100  public int setCount(@ParametricNullness E element, int count) {
101    return delegate().setCount(element, count);
102  }
103
104  @CanIgnoreReturnValue
105  @Override
106  public boolean setCount(@ParametricNullness E element, int oldCount, int newCount) {
107    return delegate().setCount(element, oldCount, newCount);
108  }
109
110  /**
111   * A sensible definition of {@link #contains} in terms of {@link #count}. If you override {@link
112   * #count}, you may wish to override {@link #contains} to forward to this implementation.
113   *
114   * @since 7.0
115   */
116  @Override
117  protected boolean standardContains(@CheckForNull Object object) {
118    return count(object) > 0;
119  }
120
121  /**
122   * A sensible definition of {@link #clear} in terms of the {@code iterator} method of {@link
123   * #entrySet}. If you override {@link #entrySet}, you may wish to override {@link #clear} to
124   * forward to this implementation.
125   *
126   * @since 7.0
127   */
128  @Override
129  protected void standardClear() {
130    Iterators.clear(entrySet().iterator());
131  }
132
133  /**
134   * A sensible, albeit inefficient, definition of {@link #count} in terms of {@link #entrySet}. If
135   * you override {@link #entrySet}, you may wish to override {@link #count} to forward to this
136   * implementation.
137   *
138   * @since 7.0
139   */
140  protected int standardCount(@CheckForNull Object object) {
141    for (Entry<?> entry : this.entrySet()) {
142      if (Objects.equal(entry.getElement(), object)) {
143        return entry.getCount();
144      }
145    }
146    return 0;
147  }
148
149  /**
150   * A sensible definition of {@link #add(Object)} in terms of {@link #add(Object, int)}. If you
151   * override {@link #add(Object, int)}, you may wish to override {@link #add(Object)} to forward to
152   * this implementation.
153   *
154   * @since 7.0
155   */
156  protected boolean standardAdd(@ParametricNullness E element) {
157    add(element, 1);
158    return true;
159  }
160
161  /**
162   * A sensible definition of {@link #addAll(Collection)} in terms of {@link #add(Object)} and
163   * {@link #add(Object, int)}. If you override either of these methods, you may wish to override
164   * {@link #addAll(Collection)} to forward to this implementation.
165   *
166   * @since 7.0
167   */
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(@CheckForNull 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(@ParametricNullness 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(@ParametricNullness 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  protected class StandardElementSet extends Multisets.ElementSet<E> {
244    /** Constructor for use by subclasses. */
245    public StandardElementSet() {}
246
247    @Override
248    Multiset<E> multiset() {
249      return ForwardingMultiset.this;
250    }
251
252    @Override
253    public Iterator<E> iterator() {
254      return Multisets.elementIterator(multiset().entrySet().iterator());
255    }
256  }
257
258  /**
259   * A sensible definition of {@link #iterator} in terms of {@link #entrySet} and {@link
260   * #remove(Object)}. If you override either of these methods, you may wish to override {@link
261   * #iterator} to forward to this implementation.
262   *
263   * @since 7.0
264   */
265  protected Iterator<E> standardIterator() {
266    return Multisets.iteratorImpl(this);
267  }
268
269  /**
270   * A sensible, albeit inefficient, definition of {@link #size} in terms of {@link #entrySet}. If
271   * you override {@link #entrySet}, you may wish to override {@link #size} to forward to this
272   * implementation.
273   *
274   * @since 7.0
275   */
276  protected int standardSize() {
277    return Multisets.linearTimeSizeImpl(this);
278  }
279
280  /**
281   * A sensible, albeit inefficient, definition of {@link #equals} in terms of {@code
282   * entrySet().size()} and {@link #count}. If you override either of these methods, you may wish to
283   * override {@link #equals} to forward to this implementation.
284   *
285   * @since 7.0
286   */
287  protected boolean standardEquals(@CheckForNull Object object) {
288    return Multisets.equalsImpl(this, object);
289  }
290
291  /**
292   * A sensible definition of {@link #hashCode} as {@code entrySet().hashCode()} . If you override
293   * {@link #entrySet}, you may wish to override {@link #hashCode} to forward to this
294   * implementation.
295   *
296   * @since 7.0
297   */
298  protected int standardHashCode() {
299    return entrySet().hashCode();
300  }
301
302  /**
303   * A sensible definition of {@link #toString} as {@code entrySet().toString()} . If you override
304   * {@link #entrySet}, you may wish to override {@link #toString} to forward to this
305   * implementation.
306   *
307   * @since 7.0
308   */
309  @Override
310  protected String standardToString() {
311    return entrySet().toString();
312  }
313}