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
017package com.google.common.collect;
018
019import com.google.common.annotations.Beta;
020import com.google.common.annotations.GwtCompatible;
021
022import java.util.Collection;
023import java.util.Iterator;
024import java.util.List;
025import java.util.ListIterator;
026
027import 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
055public 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  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  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  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  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  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  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}, {@link #get(int)}, {@link #set(int, Object)}, {@link
197   * #add(int, Object)}, and {@link #remove(int)}. If you override any of these
198   * methods, you may wish to override {@link #listIterator(int)} to forward to
199   * this implementation.
200   *
201   * @since 7.0
202   */
203  @Beta protected ListIterator<E> standardListIterator(int start) {
204    return Lists.listIteratorImpl(this, start);
205  }
206
207  /**
208   * A sensible default implementation of {@link #subList(int, int)}. If you
209   * override any other methods, you may wish to override {@link #subList(int,
210   * int)} to forward to this implementation.
211   *
212   * @since 7.0
213   */
214  @Beta protected List<E> standardSubList(int fromIndex, int toIndex) {
215    return Lists.subListImpl(this, fromIndex, toIndex);
216  }
217
218  /**
219   * A sensible definition of {@link #equals(Object)} in terms of {@link #size}
220   * and {@link #iterator}. If you override either of those methods, you may
221   * wish to override {@link #equals(Object)} to forward to this implementation.
222   *
223   * @since 7.0
224   */
225  @Beta protected boolean standardEquals(@Nullable Object object) {
226    return Lists.equalsImpl(this, object);
227  }
228
229  /**
230   * A sensible definition of {@link #hashCode} in terms of {@link #iterator}.
231   * If you override {@link #iterator}, you may wish to override {@link
232   * #hashCode} to forward to this implementation.
233   *
234   * @since 7.0
235   */
236  @Beta protected int standardHashCode() {
237    return Lists.hashCodeImpl(this);
238  }
239}