001 /*
002 * Copyright (C) 2007 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
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 2.0 (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 @Override
065 public void add(int index, E element) {
066 delegate().add(index, element);
067 }
068
069 @Override
070 public boolean addAll(int index, Collection<? extends E> elements) {
071 return delegate().addAll(index, elements);
072 }
073
074 @Override
075 public E get(int index) {
076 return delegate().get(index);
077 }
078
079 @Override
080 public int indexOf(Object element) {
081 return delegate().indexOf(element);
082 }
083
084 @Override
085 public int lastIndexOf(Object element) {
086 return delegate().lastIndexOf(element);
087 }
088
089 @Override
090 public ListIterator<E> listIterator() {
091 return delegate().listIterator();
092 }
093
094 @Override
095 public ListIterator<E> listIterator(int index) {
096 return delegate().listIterator(index);
097 }
098
099 @Override
100 public E remove(int index) {
101 return delegate().remove(index);
102 }
103
104 @Override
105 public E set(int index, E element) {
106 return delegate().set(index, element);
107 }
108
109 @Override
110 public List<E> subList(int fromIndex, int toIndex) {
111 return delegate().subList(fromIndex, toIndex);
112 }
113
114 @Override public boolean equals(@Nullable Object object) {
115 return object == this || delegate().equals(object);
116 }
117
118 @Override public int hashCode() {
119 return delegate().hashCode();
120 }
121
122 /**
123 * A sensible default implementation of {@link #add(Object)}, in terms of
124 * {@link #add(int, Object)}. If you override {@link #add(int, Object)}, you
125 * may wish to override {@link #add(Object)} to forward to this
126 * implementation.
127 *
128 * @since 7.0
129 */
130 @Beta protected boolean standardAdd(E element){
131 add(size(), element);
132 return true;
133 }
134
135 /**
136 * A sensible default implementation of {@link #addAll(int, Collection)}, in
137 * terms of the {@code add} method of {@link #listIterator(int)}. If you
138 * override {@link #listIterator(int)}, you may wish to override {@link
139 * #addAll(int, Collection)} to forward to this implementation.
140 *
141 * @since 7.0
142 */
143 @Beta protected boolean standardAddAll(
144 int index, Iterable<? extends E> elements) {
145 return Lists.addAllImpl(this, index, elements);
146 }
147
148 /**
149 * A sensible default implementation of {@link #indexOf}, in terms of {@link
150 * #listIterator()}. If you override {@link #listIterator()}, you may wish to
151 * override {@link #indexOf} to forward to this implementation.
152 *
153 * @since 7.0
154 */
155 @Beta protected int standardIndexOf(@Nullable Object element) {
156 return Lists.indexOfImpl(this, element);
157 }
158
159 /**
160 * A sensible default implementation of {@link #lastIndexOf}, in terms of
161 * {@link #listIterator(int)}. If you override {@link #listIterator(int)}, you
162 * may wish to override {@link #lastIndexOf} to forward to this
163 * implementation.
164 *
165 * @since 7.0
166 */
167 @Beta protected int standardLastIndexOf(@Nullable Object element) {
168 return Lists.lastIndexOfImpl(this, element);
169 }
170
171 /**
172 * A sensible default implementation of {@link #iterator}, in terms of
173 * {@link #listIterator()}. If you override {@link #listIterator()}, you may
174 * wish to override {@link #iterator} to forward to this implementation.
175 *
176 * @since 7.0
177 */
178 @Beta protected Iterator<E> standardIterator() {
179 return listIterator();
180 }
181
182 /**
183 * A sensible default implementation of {@link #listIterator()}, in terms of
184 * {@link #listIterator(int)}. If you override {@link #listIterator(int)}, you
185 * may wish to override {@link #listIterator()} to forward to this
186 * implementation.
187 *
188 * @since 7.0
189 */
190 @Beta protected ListIterator<E> standardListIterator(){
191 return listIterator(0);
192 }
193
194 /**
195 * A sensible default implementation of {@link #listIterator(int)}, in terms
196 * of {@link #size} and {@link #get(int)}. If you override either of these
197 * methods you may wish to override {@link #listIterator(int)} to forward to
198 * this implementation.
199 *
200 * @since 7.0
201 */
202 @Beta protected ListIterator<E> standardListIterator(int start) {
203 return Lists.listIteratorImpl(this, start);
204 }
205
206 /**
207 * A sensible default implementation of {@link #subList(int, int)}. If you
208 * override any other methods, you may wish to override {@link #subList(int,
209 * int)} to forward to this implementation.
210 *
211 * @since 7.0
212 */
213 @Beta protected List<E> standardSubList(int fromIndex, int toIndex) {
214 return Lists.subListImpl(this, fromIndex, toIndex);
215 }
216
217 /**
218 * A sensible definition of {@link #equals(Object)} in terms of {@link #size}
219 * and {@link #iterator}. If you override either of those methods, you may
220 * wish to override {@link #equals(Object)} to forward to this implementation.
221 *
222 * @since 7.0
223 */
224 @Beta protected boolean standardEquals(@Nullable Object object) {
225 return Lists.equalsImpl(this, object);
226 }
227
228 /**
229 * A sensible definition of {@link #hashCode} in terms of {@link #iterator}.
230 * If you override {@link #iterator}, you may wish to override {@link
231 * #hashCode} to forward to this implementation.
232 *
233 * @since 7.0
234 */
235 @Beta protected int standardHashCode() {
236 return Lists.hashCodeImpl(this);
237 }
238 }