1/*
2 * Copyright (C) 2007 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;
20import com.google.common.annotations.GwtCompatible;
21
22import java.util.Comparator;
23import java.util.Iterator;
24import java.util.NoSuchElementException;
25import java.util.SortedSet;
26
27import javax.annotation.Nullable;
28
29/**
30 * A sorted set which forwards all its method calls to another sorted set.
31 * Subclasses should override one or more methods to modify the behavior of the
32 * backing sorted set as desired per the <a
33 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
34 *
35 * <p><i>Warning:</i> The methods of {@code ForwardingSortedSet} forward
36 * <i>indiscriminately</i> to the methods of the delegate. For example,
37 * overriding {@link #add} alone <i>will not</i> change the behavior of {@link
38 * #addAll}, which can lead to unexpected behavior. In this case, you should
39 * override {@code addAll} as well, either providing your own implementation, or
40 * delegating to the provided {@code standardAddAll} method.
41 *
42 * <p>Each of the {@code standard} methods, where appropriate, uses the set's
43 * comparator (or the natural ordering of the elements, if there is no
44 * comparator) to test element equality. As a result, if the comparator is not
45 * consistent with equals, some of the standard implementations may violate the
46 * {@code Set} contract.
47 *
48 * <p>The {@code standard} methods and the collection views they return are not
49 * guaranteed to be thread-safe, even when all of the methods that they depend
50 * on are thread-safe.
51 *
52 * @author Mike Bostock
53 * @author Louis Wasserman
54 * @since 2.0 (imported from Google Collections Library)
55 */
56@GwtCompatible
57public abstract class ForwardingSortedSet<E> extends ForwardingSet<E>
58    implements SortedSet<E> {
59
60  /** Constructor for use by subclasses. */
61  protected ForwardingSortedSet() {}
62
63  @Override protected abstract SortedSet<E> delegate();
64
65  @Override
66  public Comparator<? super E> comparator() {
67    return delegate().comparator();
68  }
69
70  @Override
71  public E first() {
72    return delegate().first();
73  }
74
75  @Override
76  public SortedSet<E> headSet(E toElement) {
77    return delegate().headSet(toElement);
78  }
79
80  @Override
81  public E last() {
82    return delegate().last();
83  }
84
85  @Override
86  public SortedSet<E> subSet(E fromElement, E toElement) {
87    return delegate().subSet(fromElement, toElement);
88  }
89
90  @Override
91  public SortedSet<E> tailSet(E fromElement) {
92    return delegate().tailSet(fromElement);
93  }
94
95  // unsafe, but worst case is a CCE is thrown, which callers will be expecting
96  @SuppressWarnings("unchecked")
97  private int unsafeCompare(Object o1, Object o2) {
98    Comparator<? super E> comparator = comparator();
99    return (comparator == null)
100        ? ((Comparable<Object>) o1).compareTo(o2)
101        : ((Comparator<Object>) comparator).compare(o1, o2);
102  }
103
104  /**
105   * A sensible definition of {@link #contains} in terms of the {@code first()}
106   * method of {@link #tailSet}. If you override {@link #tailSet}, you may wish
107   * to override {@link #contains} to forward to this implementation.
108   *
109   * @since 7.0
110   */
111  @Override @Beta protected boolean standardContains(@Nullable Object object) {
112    try {
113      // any ClassCastExceptions are caught
114      @SuppressWarnings("unchecked")
115      SortedSet<Object> self = (SortedSet<Object>) this;
116      Object ceiling = self.tailSet(object).first();
117      return unsafeCompare(ceiling, object) == 0;
118    } catch (ClassCastException e) {
119      return false;
120    } catch (NoSuchElementException e) {
121      return false;
122    } catch (NullPointerException e) {
123      return false;
124    }
125  }
126
127  /**
128   * A sensible definition of {@link #remove} in terms of the {@code iterator()}
129   * method of {@link #tailSet}. If you override {@link #tailSet}, you may wish
130   * to override {@link #remove} to forward to this implementation.
131   *
132   * @since 7.0
133   */
134  @Override @Beta protected boolean standardRemove(@Nullable Object object) {
135    try {
136      // any ClassCastExceptions are caught
137      @SuppressWarnings("unchecked")
138      SortedSet<Object> self = (SortedSet<Object>) this;
139      Iterator<Object> iterator = self.tailSet(object).iterator();
140      if (iterator.hasNext()) {
141        Object ceiling = iterator.next();
142        if (unsafeCompare(ceiling, object) == 0) {
143          iterator.remove();
144          return true;
145        }
146      }
147    } catch (ClassCastException e) {
148      return false;
149    } catch (NullPointerException e) {
150      return false;
151    }
152    return false;
153  }
154
155  /**
156   * A sensible default implementation of {@link #subSet(Object, Object)} in
157   * terms of {@link #headSet(Object)} and {@link #tailSet(Object)}. In some
158   * situations, you may wish to override {@link #subSet(Object, Object)} to
159   * forward to this implementation.
160   *
161   * @since 7.0
162   */
163  @Beta protected SortedSet<E> standardSubSet(E fromElement, E toElement) {
164    return tailSet(fromElement).headSet(toElement);
165  }
166}
167