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.Collection;
023 import java.util.Iterator;
024 import java.util.List;
025 import java.util.ListIterator;
026
027 import javax.annotation.Nullable;
028
029 /**
030 * A list which forwards all its method calls to another list. Subclasses should
031 * override one or more methods to modify the behavior of the backing list as
032 * desired per the <a
033 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
034 *
035 * <p>This class does not implement {@link java.util.RandomAccess}. If the
036 * delegate supports random access, the {@code ForwardingList} subclass should
037 * implement the {@code RandomAccess} interface.
038 *
039 * <p><b>Warning:</b> The methods of {@code ForwardingList} forward
040 * <b>indiscriminately</b> to the methods of the delegate. For example,
041 * overriding {@link #add} alone <b>will not</b> change the behavior of {@link
042 * #addAll}, which can lead to unexpected behavior. In this case, you should
043 * override {@code addAll} as well, either providing your own implementation, or
044 * delegating to the provided {@code standardAddAll} method.
045 *
046 * <p>The {@code standard} methods and any collection views they return are not
047 * guaranteed to be thread-safe, even when all of the methods that they depend
048 * on are thread-safe.
049 *
050 * @author Mike Bostock
051 * @author Louis Wasserman
052 * @since 2 (imported from Google Collections Library)
053 */
054 @GwtCompatible
055 public abstract class ForwardingList<E> extends ForwardingCollection<E>
056 implements List<E> {
057 // TODO(user): identify places where thread safety is actually lost
058
059 /** Constructor for use by subclasses. */
060 protected ForwardingList() {}
061
062 @Override protected abstract List<E> delegate();
063
064 public void add(int index, E element) {
065 delegate().add(index, element);
066 }
067
068 public boolean addAll(int index, Collection<? extends E> elements) {
069 return delegate().addAll(index, elements);
070 }
071
072 public E get(int index) {
073 return delegate().get(index);
074 }
075
076 public int indexOf(Object element) {
077 return delegate().indexOf(element);
078 }
079
080 public int lastIndexOf(Object element) {
081 return delegate().lastIndexOf(element);
082 }
083
084 public ListIterator<E> listIterator() {
085 return delegate().listIterator();
086 }
087
088 public ListIterator<E> listIterator(int index) {
089 return delegate().listIterator(index);
090 }
091
092 public E remove(int index) {
093 return delegate().remove(index);
094 }
095
096 public E set(int index, E element) {
097 return delegate().set(index, element);
098 }
099
100 public List<E> subList(int fromIndex, int toIndex) {
101 return delegate().subList(fromIndex, toIndex);
102 }
103
104 @Override public boolean equals(@Nullable Object object) {
105 return object == this || delegate().equals(object);
106 }
107
108 @Override public int hashCode() {
109 return delegate().hashCode();
110 }
111
112 /**
113 * A sensible default implementation of {@link #add(Object)}, in terms of
114 * {@link #add(int, Object)}. If you override {@link #add(int, Object)}, you
115 * may wish to override {@link #add(Object)} to forward to this
116 * implementation.
117 *
118 * @since 7
119 */
120 @Beta protected boolean standardAdd(E element){
121 add(size(), element);
122 return true;
123 }
124
125 /**
126 * A sensible default implementation of {@link #addAll(int, Collection)}, in
127 * terms of the {@code add} method of {@link #listIterator(int)}. If you
128 * override {@link #listIterator(int)}, you may wish to override {@link
129 * #addAll(int, Collection)} to forward to this implementation.
130 *
131 * @since 7
132 */
133 @Beta protected boolean standardAddAll(
134 int index, Iterable<? extends E> elements) {
135 return Lists.addAllImpl(this, index, elements);
136 }
137
138 /**
139 * A sensible default implementation of {@link #indexOf}, in terms of {@link
140 * #listIterator()}. If you override {@link #listIterator()}, you may wish to
141 * override {@link #indexOf} to forward to this implementation.
142 *
143 * @since 7
144 */
145 @Beta protected int standardIndexOf(@Nullable Object element) {
146 return Lists.indexOfImpl(this, element);
147 }
148
149 /**
150 * A sensible default implementation of {@link #lastIndexOf}, in terms of
151 * {@link #listIterator(int)}. If you override {@link #listIterator(int)}, you
152 * may wish to override {@link #lastIndexOf} to forward to this
153 * implementation.
154 *
155 * @since 7
156 */
157 @Beta protected int standardLastIndexOf(@Nullable Object element) {
158 return Lists.lastIndexOfImpl(this, element);
159 }
160
161 /**
162 * A sensible default implementation of {@link #iterator}, in terms of
163 * {@link #listIterator()}. If you override {@link #listIterator()}, you may
164 * wish to override {@link #iterator} to forward to this implementation.
165 *
166 * @since 7
167 */
168 @Beta protected Iterator<E> standardIterator() {
169 return listIterator();
170 }
171
172 /**
173 * A sensible default implementation of {@link #listIterator()}, in terms of
174 * {@link #listIterator(int)}. If you override {@link #listIterator(int)}, you
175 * may wish to override {@link #listIterator()} to forward to this
176 * implementation.
177 *
178 * @since 7
179 */
180 @Beta protected ListIterator<E> standardListIterator(){
181 return listIterator(0);
182 }
183
184 /**
185 * A sensible default implementation of {@link #listIterator(int)}, in terms
186 * of {@link #size} and {@link #get(int)}. If you override either of these
187 * methods you may wish to override {@link #listIterator(int)} to forward to
188 * this implementation.
189 *
190 * @since 7
191 */
192 @Beta protected ListIterator<E> standardListIterator(int start) {
193 return Lists.listIteratorImpl(this, start);
194 }
195
196 /**
197 * A sensible default implementation of {@link #subList(int, int)}. If you
198 * override any other methods, you may wish to override {@link #subList(int,
199 * int)} to forward to this implementation.
200 *
201 * @since 7
202 */
203 @Beta protected List<E> standardSubList(int fromIndex, int toIndex) {
204 return Lists.subListImpl(this, fromIndex, toIndex);
205 }
206
207 /**
208 * A sensible definition of {@link #equals(Object)} in terms of {@link #size}
209 * and {@link #iterator}. If you override either of those methods, you may
210 * wish to override {@link #equals(Object)} to forward to this implementation.
211 *
212 * @since 7
213 */
214 @Beta protected boolean standardEquals(@Nullable Object object) {
215 return Lists.equalsImpl(this, object);
216 }
217
218 /**
219 * A sensible definition of {@link #hashCode} in terms of {@link #iterator}.
220 * If you override {@link #iterator}, you may wish to override {@link
221 * #hashCode} to forward to this implementation.
222 *
223 * @since 7
224 */
225 @Beta protected int standardHashCode() {
226 return Lists.hashCodeImpl(this);
227 }
228 }