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.Beta;
018import com.google.common.annotations.GwtCompatible;
019
020import java.util.Comparator;
021import java.util.Iterator;
022import java.util.NavigableSet;
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
027 * per 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
031 * {@link #add(Object, int)} alone <b>will not</b> change the behavior of {@link #add(Object)},
032 * which can lead to unexpected behavior. In this case, you should override {@code add(Object)} as
033 * well, either providing your own implementation, or delegating to the provided {@code
034 * standardAdd} method.
035 *
036 * <p>The {@code standard} methods and any collection views they return are not guaranteed to be
037 * thread-safe, even when all of the methods that they depend on are thread-safe.
038 *
039 * @author Louis Wasserman
040 * @since 15.0
041 */
042@Beta
043@GwtCompatible(emulated = true)
044public abstract class ForwardingSortedMultiset<E> extends ForwardingMultiset<E>
045    implements SortedMultiset<E> {
046  /** Constructor for use by subclasses. */
047  protected ForwardingSortedMultiset() {}
048
049  @Override
050  protected abstract SortedMultiset<E> delegate();
051
052  @Override
053  public NavigableSet<E> elementSet() {
054    return (NavigableSet<E>) super.elementSet();
055  }
056
057  /**
058   * A sensible implementation of {@link SortedMultiset#elementSet} in terms of the following
059   * methods: {@link SortedMultiset#clear}, {@link SortedMultiset#comparator}, {@link
060   * SortedMultiset#contains}, {@link SortedMultiset#containsAll}, {@link SortedMultiset#count},
061   * {@link SortedMultiset#firstEntry} {@link SortedMultiset#headMultiset}, {@link
062   * SortedMultiset#isEmpty}, {@link SortedMultiset#lastEntry}, {@link SortedMultiset#subMultiset},
063   * {@link SortedMultiset#tailMultiset}, the {@code size()} and {@code iterator()} methods of
064   * {@link SortedMultiset#entrySet}, and {@link SortedMultiset#remove(Object, int)}. In many
065   * situations, you may wish to override {@link SortedMultiset#elementSet} to forward to this
066   * implementation or a subclass thereof.
067   */
068  protected class StandardElementSet extends SortedMultisets.NavigableElementSet<E> {
069    /** Constructor for use by subclasses. */
070    public StandardElementSet() {
071      super(ForwardingSortedMultiset.this);
072    }
073  }
074
075  @Override
076  public Comparator<? super E> comparator() {
077    return delegate().comparator();
078  }
079
080  @Override
081  public SortedMultiset<E> descendingMultiset() {
082    return delegate().descendingMultiset();
083  }
084
085  /**
086   * A skeleton implementation of a descending multiset view. Normally,
087   * {@link #descendingMultiset()} will not reflect any changes you make to the behavior of methods
088   * such as {@link #add(Object)} or {@link #pollFirstEntry}. This skeleton implementation
089   * correctly delegates each of its operations to the appropriate methods of this {@code
090   * ForwardingSortedMultiset}.
091   *
092   * In many cases, you may wish to override {@link #descendingMultiset()} to return an instance of
093   * a subclass of {@code StandardDescendingMultiset}.
094   */
095  protected abstract class StandardDescendingMultiset
096      extends DescendingMultiset<E> {
097    /** Constructor for use by subclasses. */
098    public StandardDescendingMultiset() {}
099
100    @Override
101    SortedMultiset<E> forwardMultiset() {
102      return ForwardingSortedMultiset.this;
103    }
104  }
105
106  @Override
107  public Entry<E> firstEntry() {
108    return delegate().firstEntry();
109  }
110
111  /**
112   * A sensible definition of {@link #firstEntry()} in terms of {@code entrySet().iterator()}.
113   *
114   * If you override {@link #entrySet()}, you may wish to override {@link #firstEntry()} to forward
115   * to this implementation.
116   */
117  protected Entry<E> standardFirstEntry() {
118    Iterator<Entry<E>> entryIterator = entrySet().iterator();
119    if (!entryIterator.hasNext()) {
120      return null;
121    }
122    Entry<E> entry = entryIterator.next();
123    return Multisets.immutableEntry(entry.getElement(), entry.getCount());
124  }
125
126  @Override
127  public Entry<E> lastEntry() {
128    return delegate().lastEntry();
129  }
130
131  /**
132   * A sensible definition of {@link #lastEntry()} in terms of {@code
133   * descendingMultiset().entrySet().iterator()}.
134   *
135   * If you override {@link #descendingMultiset} or {@link #entrySet()}, you may wish to override
136   * {@link #firstEntry()} to forward to this implementation.
137   */
138  protected Entry<E> standardLastEntry() {
139    Iterator<Entry<E>> entryIterator = descendingMultiset()
140        .entrySet()
141        .iterator();
142    if (!entryIterator.hasNext()) {
143      return null;
144    }
145    Entry<E> entry = entryIterator.next();
146    return Multisets.immutableEntry(entry.getElement(), entry.getCount());
147  }
148
149  @Override
150  public Entry<E> pollFirstEntry() {
151    return delegate().pollFirstEntry();
152  }
153
154  /**
155   * A sensible definition of {@link #pollFirstEntry()} in terms of {@code entrySet().iterator()}.
156   *
157   * If you override {@link #entrySet()}, you may wish to override {@link #pollFirstEntry()} to
158   * forward to this implementation.
159   */
160  protected Entry<E> standardPollFirstEntry() {
161    Iterator<Entry<E>> entryIterator = entrySet().iterator();
162    if (!entryIterator.hasNext()) {
163      return null;
164    }
165    Entry<E> entry = entryIterator.next();
166    entry = Multisets.immutableEntry(entry.getElement(), entry.getCount());
167    entryIterator.remove();
168    return entry;
169  }
170
171  @Override
172  public Entry<E> pollLastEntry() {
173    return delegate().pollLastEntry();
174  }
175
176  /**
177   * A sensible definition of {@link #pollLastEntry()} in terms of {@code
178   * descendingMultiset().entrySet().iterator()}.
179   *
180   * If you override {@link #descendingMultiset()} or {@link #entrySet()}, you may wish to override
181   * {@link #pollLastEntry()} to forward to this implementation.
182   */
183  protected Entry<E> standardPollLastEntry() {
184    Iterator<Entry<E>> entryIterator = descendingMultiset()
185        .entrySet()
186        .iterator();
187    if (!entryIterator.hasNext()) {
188      return null;
189    }
190    Entry<E> entry = entryIterator.next();
191    entry = Multisets.immutableEntry(entry.getElement(), entry.getCount());
192    entryIterator.remove();
193    return entry;
194  }
195
196  @Override
197  public SortedMultiset<E> headMultiset(E upperBound, BoundType boundType) {
198    return delegate().headMultiset(upperBound, boundType);
199  }
200
201  @Override
202  public SortedMultiset<E> subMultiset(
203      E lowerBound, BoundType lowerBoundType, E upperBound, BoundType upperBoundType) {
204    return delegate().subMultiset(lowerBound, lowerBoundType, upperBound, upperBoundType);
205  }
206
207  /**
208   * A sensible definition of {@link #subMultiset(Object, BoundType, Object, BoundType)} in terms
209   * of {@link #headMultiset(Object, BoundType) headMultiset} and
210   * {@link #tailMultiset(Object, BoundType) tailMultiset}.
211   *
212   * If you override either of these methods, you may wish to override
213   * {@link #subMultiset(Object, BoundType, Object, BoundType)} to forward to this implementation.
214   */
215  protected SortedMultiset<E> standardSubMultiset(
216      E lowerBound, BoundType lowerBoundType, E upperBound, BoundType upperBoundType) {
217    return tailMultiset(lowerBound, lowerBoundType).headMultiset(upperBound, upperBoundType);
218  }
219
220  @Override
221  public SortedMultiset<E> tailMultiset(E lowerBound, BoundType boundType) {
222    return delegate().tailMultiset(lowerBound, boundType);
223  }
224
225}