001/*
002 * Copyright (C) 2011 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the
010 * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
011 * express or implied. See the License for the specific language governing permissions and
012 * limitations under the License.
013 */
014
015package com.google.common.collect;
016
017import com.google.common.annotations.GwtCompatible;
018import java.util.Comparator;
019import java.util.Iterator;
020import java.util.NavigableSet;
021import javax.annotation.CheckForNull;
022import org.checkerframework.checker.nullness.qual.Nullable;
023
024/**
025 * A sorted multiset which forwards all its method calls to another sorted multiset. Subclasses
026 * should override one or more methods to modify the behavior of the backing multiset as desired per
027 * the <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
028 *
029 * <p><b>Warning:</b> The methods of {@code ForwardingSortedMultiset} forward
030 * <b>indiscriminately</b> to the methods of the delegate. For example, overriding {@link
031 * #add(Object, int)} alone <b>will not</b> change the behavior of {@link #add(Object)}, which can
032 * lead to unexpected behavior. In this case, you should override {@code add(Object)} as well,
033 * either providing your own implementation, or delegating to the provided {@code standardAdd}
034 * method.
035 *
036 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
037 * default} methods. Instead, it inherits their default implementations. When those implementations
038 * invoke methods, they invoke methods on the {@code ForwardingSortedMultiset}.
039 *
040 * <p>The {@code standard} methods and any collection views they return are not guaranteed to be
041 * thread-safe, even when all of the methods that they depend on are thread-safe.
042 *
043 * @author Louis Wasserman
044 * @since 15.0
045 */
046@GwtCompatible(emulated = true)
047public abstract class ForwardingSortedMultiset<E extends @Nullable Object>
048    extends ForwardingMultiset<E> implements SortedMultiset<E> {
049  /** Constructor for use by subclasses. */
050  protected ForwardingSortedMultiset() {}
051
052  @Override
053  protected abstract SortedMultiset<E> delegate();
054
055  @Override
056  public NavigableSet<E> elementSet() {
057    return delegate().elementSet();
058  }
059
060  /**
061   * A sensible implementation of {@link SortedMultiset#elementSet} in terms of the following
062   * methods: {@link SortedMultiset#clear}, {@link SortedMultiset#comparator}, {@link
063   * SortedMultiset#contains}, {@link SortedMultiset#containsAll}, {@link SortedMultiset#count},
064   * {@link SortedMultiset#firstEntry} {@link SortedMultiset#headMultiset}, {@link
065   * SortedMultiset#isEmpty}, {@link SortedMultiset#lastEntry}, {@link SortedMultiset#subMultiset},
066   * {@link SortedMultiset#tailMultiset}, the {@code size()} and {@code iterator()} methods of
067   * {@link SortedMultiset#entrySet}, and {@link SortedMultiset#remove(Object, int)}. In many
068   * situations, you may wish to override {@link SortedMultiset#elementSet} to forward to this
069   * implementation or a subclass thereof.
070   *
071   * @since 15.0
072   */
073  protected class StandardElementSet extends SortedMultisets.NavigableElementSet<E> {
074    /** Constructor for use by subclasses. */
075    public StandardElementSet() {
076      super(ForwardingSortedMultiset.this);
077    }
078  }
079
080  @Override
081  public Comparator<? super E> comparator() {
082    return delegate().comparator();
083  }
084
085  @Override
086  public SortedMultiset<E> descendingMultiset() {
087    return delegate().descendingMultiset();
088  }
089
090  /**
091   * A skeleton implementation of a descending multiset view. Normally, {@link
092   * #descendingMultiset()} will not reflect any changes you make to the behavior of methods such as
093   * {@link #add(Object)} or {@link #pollFirstEntry}. This skeleton implementation correctly
094   * delegates each of its operations to the appropriate methods of this {@code
095   * ForwardingSortedMultiset}.
096   *
097   * <p>In many cases, you may wish to override {@link #descendingMultiset()} to return an instance
098   * of a subclass of {@code StandardDescendingMultiset}.
099   *
100   * @since 15.0
101   */
102  protected abstract class StandardDescendingMultiset extends DescendingMultiset<E> {
103    /** Constructor for use by subclasses. */
104    public StandardDescendingMultiset() {}
105
106    @Override
107    SortedMultiset<E> forwardMultiset() {
108      return ForwardingSortedMultiset.this;
109    }
110  }
111
112  @Override
113  @CheckForNull
114  public Entry<E> firstEntry() {
115    return delegate().firstEntry();
116  }
117
118  /**
119   * A sensible definition of {@link #firstEntry()} in terms of {@code entrySet().iterator()}.
120   *
121   * <p>If you override {@link #entrySet()}, you may wish to override {@link #firstEntry()} to
122   * forward to this implementation.
123   */
124  @CheckForNull
125  protected Entry<E> standardFirstEntry() {
126    Iterator<Entry<E>> entryIterator = entrySet().iterator();
127    if (!entryIterator.hasNext()) {
128      return null;
129    }
130    Entry<E> entry = entryIterator.next();
131    return Multisets.immutableEntry(entry.getElement(), entry.getCount());
132  }
133
134  @Override
135  @CheckForNull
136  public Entry<E> lastEntry() {
137    return delegate().lastEntry();
138  }
139
140  /**
141   * A sensible definition of {@link #lastEntry()} in terms of {@code
142   * descendingMultiset().entrySet().iterator()}.
143   *
144   * <p>If you override {@link #descendingMultiset} or {@link #entrySet()}, you may wish to override
145   * {@link #firstEntry()} to forward to this implementation.
146   */
147  @CheckForNull
148  protected Entry<E> standardLastEntry() {
149    Iterator<Entry<E>> entryIterator = descendingMultiset().entrySet().iterator();
150    if (!entryIterator.hasNext()) {
151      return null;
152    }
153    Entry<E> entry = entryIterator.next();
154    return Multisets.immutableEntry(entry.getElement(), entry.getCount());
155  }
156
157  @Override
158  @CheckForNull
159  public Entry<E> pollFirstEntry() {
160    return delegate().pollFirstEntry();
161  }
162
163  /**
164   * A sensible definition of {@link #pollFirstEntry()} in terms of {@code entrySet().iterator()}.
165   *
166   * <p>If you override {@link #entrySet()}, you may wish to override {@link #pollFirstEntry()} to
167   * forward to this implementation.
168   */
169  @CheckForNull
170  protected Entry<E> standardPollFirstEntry() {
171    Iterator<Entry<E>> entryIterator = entrySet().iterator();
172    if (!entryIterator.hasNext()) {
173      return null;
174    }
175    Entry<E> entry = entryIterator.next();
176    entry = Multisets.immutableEntry(entry.getElement(), entry.getCount());
177    entryIterator.remove();
178    return entry;
179  }
180
181  @Override
182  @CheckForNull
183  public Entry<E> pollLastEntry() {
184    return delegate().pollLastEntry();
185  }
186
187  /**
188   * A sensible definition of {@link #pollLastEntry()} in terms of {@code
189   * descendingMultiset().entrySet().iterator()}.
190   *
191   * <p>If you override {@link #descendingMultiset()} or {@link #entrySet()}, you may wish to
192   * override {@link #pollLastEntry()} to forward to this implementation.
193   */
194  @CheckForNull
195  protected Entry<E> standardPollLastEntry() {
196    Iterator<Entry<E>> entryIterator = descendingMultiset().entrySet().iterator();
197    if (!entryIterator.hasNext()) {
198      return null;
199    }
200    Entry<E> entry = entryIterator.next();
201    entry = Multisets.immutableEntry(entry.getElement(), entry.getCount());
202    entryIterator.remove();
203    return entry;
204  }
205
206  @Override
207  public SortedMultiset<E> headMultiset(@ParametricNullness E upperBound, BoundType boundType) {
208    return delegate().headMultiset(upperBound, boundType);
209  }
210
211  @Override
212  public SortedMultiset<E> subMultiset(
213      @ParametricNullness E lowerBound,
214      BoundType lowerBoundType,
215      @ParametricNullness E upperBound,
216      BoundType upperBoundType) {
217    return delegate().subMultiset(lowerBound, lowerBoundType, upperBound, upperBoundType);
218  }
219
220  /**
221   * A sensible definition of {@link #subMultiset(Object, BoundType, Object, BoundType)} in terms of
222   * {@link #headMultiset(Object, BoundType) headMultiset} and {@link #tailMultiset(Object,
223   * BoundType) tailMultiset}.
224   *
225   * <p>If you override either of these methods, you may wish to override {@link
226   * #subMultiset(Object, BoundType, Object, BoundType)} to forward to this implementation.
227   */
228  protected SortedMultiset<E> standardSubMultiset(
229      @ParametricNullness E lowerBound,
230      BoundType lowerBoundType,
231      @ParametricNullness E upperBound,
232      BoundType upperBoundType) {
233    return tailMultiset(lowerBound, lowerBoundType).headMultiset(upperBound, upperBoundType);
234  }
235
236  @Override
237  public SortedMultiset<E> tailMultiset(@ParametricNullness E lowerBound, BoundType boundType) {
238    return delegate().tailMultiset(lowerBound, boundType);
239  }
240}