1/*
2 * Copyright (C) 2012 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.collect;
18
19import com.google.common.annotations.Beta;
20
21import java.util.Iterator;
22import java.util.NavigableSet;
23import java.util.SortedSet;
24
25/**
26 * A navigable set which forwards all its method calls to another navigable set. Subclasses should
27 * override one or more methods to modify the behavior of the backing set as desired per the <a
28 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
29 *
30 * <p><i>Warning:</i> The methods of {@code ForwardingNavigableSet} forward <i>indiscriminately</i>
31 * to the methods of the delegate. For example, overriding {@link #add} alone <i>will not</i>
32 * change the behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you
33 * should override {@code addAll} as well, either providing your own implementation, or delegating
34 * to the provided {@code standardAddAll} method.
35 *
36 * <p>Each of the {@code standard} methods uses the set's comparator (or the natural ordering of
37 * the elements, if there is no comparator) to test element equality. As a result, if the
38 * comparator is not consistent with equals, some of the standard implementations may violate the
39 * {@code Set} contract.
40 *
41 * <p>The {@code standard} methods and the collection views they return are not guaranteed to be
42 * thread-safe, even when all of the methods that they depend on are thread-safe.
43 *
44 * @author Louis Wasserman
45 * @since 12.0
46 */
47public abstract class ForwardingNavigableSet<E>
48    extends ForwardingSortedSet<E> implements NavigableSet<E> {
49
50  /** Constructor for use by subclasses. */
51  protected ForwardingNavigableSet() {}
52
53  @Override
54  protected abstract NavigableSet<E> delegate();
55
56  @Override
57  public E lower(E e) {
58    return delegate().lower(e);
59  }
60
61  /**
62   * A sensible definition of {@link #lower} in terms of the {@code descendingIterator} method of
63   * {@link #headSet(Object, boolean)}. If you override {@link #headSet(Object, boolean)}, you may
64   * wish to override {@link #lower} to forward to this implementation.
65   */
66  protected E standardLower(E e) {
67    return Iterators.getNext(headSet(e, false).descendingIterator(), null);
68  }
69
70  @Override
71  public E floor(E e) {
72    return delegate().floor(e);
73  }
74
75  /**
76   * A sensible definition of {@link #floor} in terms of the {@code descendingIterator} method of
77   * {@link #headSet(Object, boolean)}. If you override {@link #headSet(Object, boolean)}, you may
78   * wish to override {@link #floor} to forward to this implementation.
79   */
80  protected E standardFloor(E e) {
81    return Iterators.getNext(headSet(e, true).descendingIterator(), null);
82  }
83
84  @Override
85  public E ceiling(E e) {
86    return delegate().ceiling(e);
87  }
88
89  /**
90   * A sensible definition of {@link #ceiling} in terms of the {@code iterator} method of
91   * {@link #tailSet(Object, boolean)}. If you override {@link #tailSet(Object, boolean)}, you may
92   * wish to override {@link #ceiling} to forward to this implementation.
93   */
94  protected E standardCeiling(E e) {
95    return Iterators.getNext(tailSet(e, true).iterator(), null);
96  }
97
98  @Override
99  public E higher(E e) {
100    return delegate().higher(e);
101  }
102
103  /**
104   * A sensible definition of {@link #higher} in terms of the {@code iterator} method of
105   * {@link #tailSet(Object, boolean)}. If you override {@link #tailSet(Object, boolean)}, you may
106   * wish to override {@link #higher} to forward to this implementation.
107   */
108  protected E standardHigher(E e) {
109    return Iterators.getNext(tailSet(e, false).iterator(), null);
110  }
111
112  @Override
113  public E pollFirst() {
114    return delegate().pollFirst();
115  }
116
117  /**
118   * A sensible definition of {@link #pollFirst} in terms of the {@code iterator} method. If you
119   * override {@link #iterator} you may wish to override {@link #pollFirst} to forward to this
120   * implementation.
121   */
122  protected E standardPollFirst() {
123    return Iterators.pollNext(iterator());
124  }
125
126  @Override
127  public E pollLast() {
128    return delegate().pollLast();
129  }
130
131  /**
132   * A sensible definition of {@link #pollLast} in terms of the {@code descendingIterator} method.
133   * If you override {@link #descendingIterator} you may wish to override {@link #pollLast} to
134   * forward to this implementation.
135   */
136  protected E standardPollLast() {
137    return Iterators.pollNext(descendingIterator());
138  }
139
140  protected E standardFirst() {
141    return iterator().next();
142  }
143
144  protected E standardLast() {
145    return descendingIterator().next();
146  }
147
148  @Override
149  public NavigableSet<E> descendingSet() {
150    return delegate().descendingSet();
151  }
152
153  /**
154   * A sensible implementation of {@link NavigableSet#descendingSet} in terms of the other methods
155   * of {@link NavigableSet}, notably including {@link NavigableSet#descendingIterator}.
156   *
157   * <p>In many cases, you may wish to override {@link ForwardingNavigableSet#descendingSet} to
158   * forward to this implementation or a subclass thereof.
159   *
160   * @since 12.0
161   */
162  @Beta
163  protected class StandardDescendingSet extends Sets.DescendingSet<E> {
164    /** Constructor for use by subclasses. */
165    public StandardDescendingSet() {
166      super(ForwardingNavigableSet.this);
167    }
168  }
169
170  @Override
171  public Iterator<E> descendingIterator() {
172    return delegate().descendingIterator();
173  }
174
175  @Override
176  public NavigableSet<E> subSet(
177      E fromElement,
178      boolean fromInclusive,
179      E toElement,
180      boolean toInclusive) {
181    return delegate().subSet(fromElement, fromInclusive, toElement, toInclusive);
182  }
183
184  /**
185   * A sensible definition of {@link #subSet(Object, boolean, Object, boolean)} in terms of the
186   * {@code headSet} and {@code tailSet} methods. In many cases, you may wish to override
187   * {@link #subSet(Object, boolean, Object, boolean)} to forward to this implementation.
188   */
189  @Beta
190  protected NavigableSet<E> standardSubSet(
191      E fromElement,
192      boolean fromInclusive,
193      E toElement,
194      boolean toInclusive) {
195    return tailSet(fromElement, fromInclusive).headSet(toElement, toInclusive);
196  }
197
198  /**
199   * A sensible definition of {@link #subSet(Object, Object)} in terms of the
200   * {@link #subSet(Object, boolean, Object, boolean)} method. If you override
201   * {@link #subSet(Object, boolean, Object, boolean)}, you may wish to override
202   * {@link #subSet(Object, Object)} to forward to this implementation.
203   */
204  @Override
205  protected SortedSet<E> standardSubSet(E fromElement, E toElement) {
206    return subSet(fromElement, true, toElement, false);
207  }
208
209  @Override
210  public NavigableSet<E> headSet(E toElement, boolean inclusive) {
211    return delegate().headSet(toElement, inclusive);
212  }
213
214  /**
215   * A sensible definition of {@link #headSet(Object)} in terms of the
216   * {@link #headSet(Object, boolean)} method. If you override
217   * {@link #headSet(Object, boolean)}, you may wish to override
218   * {@link #headSet(Object)} to forward to this implementation.
219   */
220  protected SortedSet<E> standardHeadSet(E toElement) {
221    return headSet(toElement, false);
222  }
223
224  @Override
225  public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
226    return delegate().tailSet(fromElement, inclusive);
227  }
228
229  /**
230   * A sensible definition of {@link #tailSet(Object)} in terms of the
231   * {@link #tailSet(Object, boolean)} method. If you override
232   * {@link #tailSet(Object, boolean)}, you may wish to override
233   * {@link #tailSet(Object)} to forward to this implementation.
234   */
235  protected SortedSet<E> standardTailSet(E fromElement) {
236    return tailSet(fromElement, true);
237  }
238}
239