001/*
002 * Copyright (C) 2012 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;
020
021import java.util.Iterator;
022import java.util.NavigableSet;
023import java.util.SortedSet;
024
025import javax.annotation.Nullable;
026
027/**
028 * A navigable set which forwards all its method calls to another navigable set. Subclasses should
029 * override one or more methods to modify the behavior of the backing set as desired per the <a
030 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
031 *
032 * <p><i>Warning:</i> The methods of {@code ForwardingNavigableSet} forward <i>indiscriminately</i>
033 * to the methods of the delegate. For example, overriding {@link #add} alone <i>will not</i>
034 * change the behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you
035 * should override {@code addAll} as well, either providing your own implementation, or delegating
036 * to the provided {@code standardAddAll} method.
037 *
038 * <p>Each of the {@code standard} methods uses the set's comparator (or the natural ordering of
039 * the elements, if there is no comparator) to test element equality. As a result, if the
040 * comparator is not consistent with equals, some of the standard implementations may violate the
041 * {@code Set} contract.
042 *
043 * <p>The {@code standard} methods and the 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 Louis Wasserman
047 * @since 12.0
048 */
049@Beta
050public abstract class ForwardingNavigableSet<E>
051    extends ForwardingSortedSet<E> implements NavigableSet<E> {
052
053  /** Constructor for use by subclasses. */
054  protected ForwardingNavigableSet() {}
055
056  @Override
057  protected abstract NavigableSet<E> delegate();
058
059  @Override
060  public E lower(E e) {
061    return delegate().lower(e);
062  }
063
064  /**
065   * A sensible definition of {@link #lower} in terms of the {@code descendingIterator} method of
066   * {@link #headSet(Object, boolean)}. If you override {@link #headSet(Object, boolean)}, you may
067   * wish to override {@link #lower} to forward to this implementation.
068   */
069  protected E standardLower(E e) {
070    return Iterators.getNext(headSet(e, false).descendingIterator(), null);
071  }
072
073  @Override
074  public E floor(E e) {
075    return delegate().floor(e);
076  }
077
078  /**
079   * A sensible definition of {@link #floor} in terms of the {@code descendingIterator} method of
080   * {@link #headSet(Object, boolean)}. If you override {@link #headSet(Object, boolean)}, you may
081   * wish to override {@link #floor} to forward to this implementation.
082   */
083  protected E standardFloor(E e) {
084    return Iterators.getNext(headSet(e, true).descendingIterator(), null);
085  }
086
087  @Override
088  public E ceiling(E e) {
089    return delegate().ceiling(e);
090  }
091
092  /**
093   * A sensible definition of {@link #ceiling} in terms of the {@code iterator} method of
094   * {@link #tailSet(Object, boolean)}. If you override {@link #tailSet(Object, boolean)}, you may
095   * wish to override {@link #ceiling} to forward to this implementation.
096   */
097  protected E standardCeiling(E e) {
098    return Iterators.getNext(tailSet(e, true).iterator(), null);
099  }
100
101  @Override
102  public E higher(E e) {
103    return delegate().higher(e);
104  }
105
106  /**
107   * A sensible definition of {@link #higher} in terms of the {@code iterator} method of
108   * {@link #tailSet(Object, boolean)}. If you override {@link #tailSet(Object, boolean)}, you may
109   * wish to override {@link #higher} to forward to this implementation.
110   */
111  protected E standardHigher(E e) {
112    return Iterators.getNext(tailSet(e, false).iterator(), null);
113  }
114
115  @Override
116  public E pollFirst() {
117    return delegate().pollFirst();
118  }
119
120  /**
121   * A sensible definition of {@link #pollFirst} in terms of the {@code iterator} method. If you
122   * override {@link #iterator} you may wish to override {@link #pollFirst} to forward to this
123   * implementation.
124   */
125  protected E standardPollFirst() {
126    return poll(iterator());
127  }
128
129  @Override
130  public E pollLast() {
131    return delegate().pollLast();
132  }
133
134  /**
135   * A sensible definition of {@link #pollLast} in terms of the {@code descendingIterator} method.
136   * If you override {@link #descendingIterator} you may wish to override {@link #pollLast} to
137   * forward to this implementation.
138   */
139  protected E standardPollLast() {
140    return poll(delegate().descendingIterator());
141  }
142
143  protected E standardFirst() {
144    return iterator().next();
145  }
146
147  protected E standardLast() {
148    return descendingIterator().next();
149  }
150
151  @Override
152  public NavigableSet<E> descendingSet() {
153    return delegate().descendingSet();
154  }
155
156  /**
157   * A sensible implementation of {@link NavigableSet#descendingSet} in terms of the other methods
158   * of {@link NavigableSet}, notably including {@link NavigableSet#descendingIterator}.
159   *
160   * <p>In many cases, you may wish to override {@link ForwardingNavigableSet#descendingSet} to
161   * forward to this implementation or a subclass thereof.
162   *
163   * @since 12.0
164   */
165  @Beta
166  protected class StandardDescendingSet extends Sets.DescendingSet<E> {
167    /** Constructor for use by subclasses. */
168    public StandardDescendingSet() {
169      super(ForwardingNavigableSet.this);
170    }
171  }
172
173  @Override
174  public Iterator<E> descendingIterator() {
175    return delegate().descendingIterator();
176  }
177
178  @Override
179  public NavigableSet<E> subSet(
180      E fromElement,
181      boolean fromInclusive,
182      E toElement,
183      boolean toInclusive) {
184    return delegate().subSet(fromElement, fromInclusive, toElement, toInclusive);
185  }
186
187  /**
188   * A sensible definition of {@link #subSet(Object, boolean, Object, boolean)} in terms of the
189   * {@code headSet} and {@code tailSet} methods. In many cases, you may wish to override
190   * {@link #subSet(Object, boolean, Object, boolean)} to forward to this implementation.
191   */
192  protected NavigableSet<E> standardSubSet(
193      E fromElement,
194      boolean fromInclusive,
195      E toElement,
196      boolean toInclusive) {
197    return tailSet(fromElement, fromInclusive).headSet(toElement, toInclusive);
198  }
199
200  /**
201   * A sensible definition of {@link #subSet(Object, Object)} in terms of the
202   * {@link #subSet(Object, boolean, Object, boolean)} method. If you override
203   * {@link #subSet(Object, boolean, Object, boolean)}, you may wish to override
204   * {@link #subSet(Object, Object)} to forward to this implementation.
205   */
206  @Override
207  protected SortedSet<E> standardSubSet(E fromElement, E toElement) {
208    return subSet(fromElement, true, toElement, false);
209  }
210
211  @Override
212  public NavigableSet<E> headSet(E toElement, boolean inclusive) {
213    return delegate().headSet(toElement, inclusive);
214  }
215
216  /**
217   * A sensible definition of {@link #headSet(Object)} in terms of the
218   * {@link #headSet(Object, boolean)} method. If you override
219   * {@link #headSet(Object, boolean)}, you may wish to override
220   * {@link #headSet(Object)} to forward to this implementation.
221   */
222  protected SortedSet<E> standardHeadSet(E toElement) {
223    return headSet(toElement, false);
224  }
225
226  @Override
227  public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
228    return delegate().tailSet(fromElement, inclusive);
229  }
230
231  /**
232   * A sensible definition of {@link #tailSet(Object)} in terms of the
233   * {@link #tailSet(Object, boolean)} method. If you override
234   * {@link #tailSet(Object, boolean)}, you may wish to override
235   * {@link #tailSet(Object)} to forward to this implementation.
236   */
237  protected SortedSet<E> standardTailSet(E fromElement) {
238    return tailSet(fromElement, true);
239  }
240
241  @Nullable
242  private E poll(Iterator<E> iterator) {
243    if (iterator.hasNext()) {
244      E result = iterator.next();
245      iterator.remove();
246      return result;
247    }
248    return null;
249  }
250}