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 org.checkerframework.checker.nullness.qual.Nullable;
026
027/**
028 * A multiset which forwards all its method calls to another multiset. Subclasses should override
029 * one or more methods to modify the behavior of the backing multiset as desired per the <a
030 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
031 *
032 * <p><b>Warning:</b> The methods of {@code ForwardingMultiset} forward <b>indiscriminately</b> to
033 * the methods of the delegate. For example, overriding {@link #add(Object, int)} alone <b>will
034 * not</b> change the behavior of {@link #add(Object)}, which can lead to unexpected behavior. In
035 * this case, you should override {@code add(Object)} as well, either providing your own
036 * implementation, or delegating to the provided {@code standardAdd} method.
037 *
038 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
039 * default} methods. Instead, it inherits their default implementations. When those implementations
040 * invoke methods, they invoke methods on the {@code ForwardingMultiset}.
041 *
042 * <p>The {@code standard} methods and any collection views they return are not guaranteed to be
043 * thread-safe, even when all of the methods that they depend on are thread-safe.
044 *
045 * @author Kevin Bourrillion
046 * @author Louis Wasserman
047 * @since 2.0
048 */
049@GwtCompatible
050public abstract class ForwardingMultiset<E extends @Nullable Object> extends ForwardingCollection<E>
051    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(@Nullable Object element) {
061    return delegate().count(element);
062  }
063
064  @CanIgnoreReturnValue
065  @Override
066  public int add(@ParametricNullness E element, int occurrences) {
067    return delegate().add(element, occurrences);
068  }
069
070  @CanIgnoreReturnValue
071  @Override
072  public int remove(@Nullable 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(@Nullable 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(@ParametricNullness E element, int count) {
099    return delegate().setCount(element, count);
100  }
101
102  @CanIgnoreReturnValue
103  @Override
104  public boolean setCount(@ParametricNullness 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(@Nullable 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  protected int standardCount(@Nullable Object object) {
139    for (Entry<?> entry : this.entrySet()) {
140      if (Objects.equal(entry.getElement(), object)) {
141        return entry.getCount();
142      }
143    }
144    return 0;
145  }
146
147  /**
148   * A sensible definition of {@link #add(Object)} in terms of {@link #add(Object, int)}. If you
149   * override {@link #add(Object, int)}, you may wish to override {@link #add(Object)} to forward to
150   * this implementation.
151   *
152   * @since 7.0
153   */
154  protected boolean standardAdd(@ParametricNullness E element) {
155    add(element, 1);
156    return true;
157  }
158
159  /**
160   * A sensible definition of {@link #addAll(Collection)} in terms of {@link #add(Object)} and
161   * {@link #add(Object, int)}. If you override either of these methods, you may wish to override
162   * {@link #addAll(Collection)} to forward to this implementation.
163   *
164   * @since 7.0
165   */
166  @Override
167  protected boolean standardAddAll(Collection<? extends E> elementsToAdd) {
168    return Multisets.addAllImpl(this, elementsToAdd);
169  }
170
171  /**
172   * A sensible definition of {@link #remove(Object)} in terms of {@link #remove(Object, int)}. If
173   * you override {@link #remove(Object, int)}, you may wish to override {@link #remove(Object)} to
174   * forward to this implementation.
175   *
176   * @since 7.0
177   */
178  @Override
179  protected boolean standardRemove(@Nullable Object element) {
180    return remove(element, 1) > 0;
181  }
182
183  /**
184   * A sensible definition of {@link #removeAll} in terms of the {@code removeAll} method of {@link
185   * #elementSet}. If you override {@link #elementSet}, you may wish to override {@link #removeAll}
186   * to forward to this implementation.
187   *
188   * @since 7.0
189   */
190  @Override
191  protected boolean standardRemoveAll(Collection<?> elementsToRemove) {
192    return Multisets.removeAllImpl(this, elementsToRemove);
193  }
194
195  /**
196   * A sensible definition of {@link #retainAll} in terms of the {@code retainAll} method of {@link
197   * #elementSet}. If you override {@link #elementSet}, you may wish to override {@link #retainAll}
198   * to forward to this implementation.
199   *
200   * @since 7.0
201   */
202  @Override
203  protected boolean standardRetainAll(Collection<?> elementsToRetain) {
204    return Multisets.retainAllImpl(this, elementsToRetain);
205  }
206
207  /**
208   * A sensible definition of {@link #setCount(Object, int)} in terms of {@link #count(Object)},
209   * {@link #add(Object, int)}, and {@link #remove(Object, int)}. {@link #entrySet()}. If you
210   * override any of these methods, you may wish to override {@link #setCount(Object, int)} to
211   * forward to this implementation.
212   *
213   * @since 7.0
214   */
215  protected int standardSetCount(@ParametricNullness E element, int count) {
216    return Multisets.setCountImpl(this, element, count);
217  }
218
219  /**
220   * A sensible definition of {@link #setCount(Object, int, int)} in terms of {@link #count(Object)}
221   * and {@link #setCount(Object, int)}. If you override either of these methods, you may wish to
222   * override {@link #setCount(Object, int, int)} to forward to this implementation.
223   *
224   * @since 7.0
225   */
226  protected boolean standardSetCount(@ParametricNullness E element, int oldCount, int newCount) {
227    return Multisets.setCountImpl(this, element, oldCount, newCount);
228  }
229
230  /**
231   * A sensible implementation of {@link Multiset#elementSet} in terms of the following methods:
232   * {@link ForwardingMultiset#clear}, {@link ForwardingMultiset#contains}, {@link
233   * ForwardingMultiset#containsAll}, {@link ForwardingMultiset#count}, {@link
234   * ForwardingMultiset#isEmpty}, the {@link Set#size} and {@link Set#iterator} methods of {@link
235   * ForwardingMultiset#entrySet}, and {@link ForwardingMultiset#remove(Object, int)}. In many
236   * situations, you may wish to override {@link ForwardingMultiset#elementSet} to forward to this
237   * implementation or a subclass thereof.
238   *
239   * @since 10.0
240   */
241  protected class StandardElementSet extends Multisets.ElementSet<E> {
242    /** Constructor for use by subclasses. */
243    public StandardElementSet() {}
244
245    @Override
246    Multiset<E> multiset() {
247      return ForwardingMultiset.this;
248    }
249
250    @Override
251    public Iterator<E> iterator() {
252      return Multisets.elementIterator(multiset().entrySet().iterator());
253    }
254  }
255
256  /**
257   * A sensible definition of {@link #iterator} in terms of {@link #entrySet} and {@link
258   * #remove(Object)}. If you override either of these methods, you may wish to override {@link
259   * #iterator} to forward to this implementation.
260   *
261   * @since 7.0
262   */
263  protected Iterator<E> standardIterator() {
264    return Multisets.iteratorImpl(this);
265  }
266
267  /**
268   * A sensible, albeit inefficient, definition of {@link #size} in terms of {@link #entrySet}. If
269   * you override {@link #entrySet}, you may wish to override {@link #size} to forward to this
270   * implementation.
271   *
272   * @since 7.0
273   */
274  protected int standardSize() {
275    return Multisets.linearTimeSizeImpl(this);
276  }
277
278  /**
279   * A sensible, albeit inefficient, definition of {@link #equals} in terms of {@code
280   * entrySet().size()} and {@link #count}. If you override either of these methods, you may wish to
281   * override {@link #equals} to forward to this implementation.
282   *
283   * @since 7.0
284   */
285  protected boolean standardEquals(@Nullable Object object) {
286    return Multisets.equalsImpl(this, object);
287  }
288
289  /**
290   * A sensible definition of {@link #hashCode} as {@code entrySet().hashCode()} . If you override
291   * {@link #entrySet}, you may wish to override {@link #hashCode} to forward to this
292   * implementation.
293   *
294   * @since 7.0
295   */
296  protected int standardHashCode() {
297    return entrySet().hashCode();
298  }
299
300  /**
301   * A sensible definition of {@link #toString} as {@code entrySet().toString()} . If you override
302   * {@link #entrySet}, you may wish to override {@link #toString} to forward to this
303   * implementation.
304   *
305   * @since 7.0
306   */
307  @Override
308  protected String standardToString() {
309    return entrySet().toString();
310  }
311}