001 /*
002 * Copyright (C) 2007 Google Inc.
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
017 package com.google.common.collect;
018
019 import com.google.common.annotations.Beta;
020 import com.google.common.annotations.GwtCompatible;
021
022 import java.util.Comparator;
023 import java.util.Iterator;
024 import java.util.NoSuchElementException;
025 import java.util.SortedSet;
026
027 import javax.annotation.Nullable;
028
029 /**
030 * A sorted set which forwards all its method calls to another sorted set.
031 * Subclasses should override one or more methods to modify the behavior of the
032 * backing sorted set as desired per the <a
033 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
034 *
035 * <p><em>Warning</em>: The methods of {@code ForwardingSortedSet} forward
036 * <em>indiscriminately</em> to the methods of the delegate. For example,
037 * overriding {@link #add} alone <em>will not</em> change the behavior of {@link
038 * #addAll}, which can lead to unexpected behavior. In this case, you should
039 * override {@code addAll} as well, either providing your own implementation, or
040 * delegating to the provided {@code standardAddAll} method.
041 *
042 * <p>Each of the {@code standard} methods, where appropriate, uses the set's
043 * comparator (or the natural ordering of the elements, if there is no
044 * comparator) to test element equality. As a result, if the comparator is not
045 * consistent with equals, some of the standard implementations may violate the
046 * {@code Set} contract.
047 *
048 * <p>The {@code standard} methods and the collection views they return are not
049 * guaranteed to be thread-safe, even when all of the methods that they depend
050 * on are thread-safe.
051 *
052 * @author Mike Bostock
053 * @author Louis Wasserman
054 * @since 2 (imported from Google Collections Library)
055 */
056 @GwtCompatible
057 public abstract class ForwardingSortedSet<E> extends ForwardingSet<E>
058 implements SortedSet<E> {
059
060 /** Constructor for use by subclasses. */
061 protected ForwardingSortedSet() {}
062
063 @Override protected abstract SortedSet<E> delegate();
064
065 public Comparator<? super E> comparator() {
066 return delegate().comparator();
067 }
068
069 public E first() {
070 return delegate().first();
071 }
072
073 public SortedSet<E> headSet(E toElement) {
074 return delegate().headSet(toElement);
075 }
076
077 public E last() {
078 return delegate().last();
079 }
080
081 public SortedSet<E> subSet(E fromElement, E toElement) {
082 return delegate().subSet(fromElement, toElement);
083 }
084
085 public SortedSet<E> tailSet(E fromElement) {
086 return delegate().tailSet(fromElement);
087 }
088
089 // unsafe, but worst case is a CCE is thrown, which callers will be expecting
090 @SuppressWarnings("unchecked")
091 private int unsafeCompare(Object o1, Object o2) {
092 Comparator<? super E> comparator = comparator();
093 return (comparator == null) ? ((Comparable) o1).compareTo(o2)
094 : ((Comparator) comparator).compare(o1, o2);
095 }
096
097 /**
098 * A sensible definition of {@link #contains} in terms of the {@code first()}
099 * method of {@link #tailSet}. If you override {@link #tailSet}, you may wish
100 * to override {@link #contains} to forward to this implementation.
101 *
102 * @since 7
103 */
104 @Override @Beta protected boolean standardContains(@Nullable Object object) {
105 try {
106 // any ClassCastExceptions are caught
107 @SuppressWarnings("unchecked")
108 SortedSet<Object> self = (SortedSet) this;
109 Object ceiling = self.tailSet(object).first();
110 return unsafeCompare(ceiling, object) == 0;
111 } catch (ClassCastException e) {
112 return false;
113 } catch (NoSuchElementException e) {
114 return false;
115 } catch (NullPointerException e) {
116 return false;
117 }
118 }
119
120 /**
121 * A sensible definition of {@link #remove} in terms of the {@code iterator()}
122 * method of {@link #tailSet}. If you override {@link #tailSet}, you may wish
123 * to override {@link #remove} to forward to this implementation.
124 *
125 * @since 7
126 */
127 @Override @Beta protected boolean standardRemove(@Nullable Object object) {
128 try {
129 // any ClassCastExceptions are caught
130 @SuppressWarnings("unchecked")
131 SortedSet<Object> self = (SortedSet) this;
132 Iterator<Object> iterator = self.tailSet(object).iterator();
133 if (iterator.hasNext()) {
134 Object ceiling = iterator.next();
135 if (unsafeCompare(ceiling, object) == 0) {
136 iterator.remove();
137 return true;
138 }
139 }
140 } catch (ClassCastException e) {
141 return false;
142 } catch (NullPointerException e) {
143 return false;
144 }
145 return false;
146 }
147
148 /**
149 * A sensible default implementation of {@link #subSet(Object, Object)} in
150 * terms of {@link #headSet(Object)} and {@link #tailSet(Object)}. In some
151 * situations, you may wish to override {@link #subSet(Object, Object)} to
152 * forward to this implementation.
153 *
154 * @since 7
155 */
156 @Beta protected SortedSet<E> standardSubSet(E fromElement, E toElement) {
157 return tailSet(fromElement).headSet(toElement);
158 }
159 }