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.GwtCompatible;
020import com.google.errorprone.annotations.CanIgnoreReturnValue;
021import java.util.Collection;
022import java.util.Iterator;
023import java.util.List;
024import java.util.ListIterator;
025import javax.annotation.CheckForNull;
026import org.checkerframework.checker.nullness.qual.Nullable;
027
028/**
029 * A list which forwards all its method calls to another list. Subclasses should override one or
030 * more methods to modify the behavior of the backing list as desired per the <a
031 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
032 *
033 * <p>This class does not implement {@link java.util.RandomAccess}. If the delegate supports random
034 * access, the {@code ForwardingList} subclass should implement the {@code RandomAccess} interface.
035 *
036 * <p><b>Warning:</b> The methods of {@code ForwardingList} forward <b>indiscriminately</b> to the
037 * methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change the
038 * behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should
039 * override {@code addAll} as well, either providing your own implementation, or delegating to the
040 * provided {@code standardAddAll} method.
041 *
042 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
043 * default} methods. Instead, it inherits their default implementations. When those implementations
044 * invoke methods, they invoke methods on the {@code ForwardingList}.
045 *
046 * <p>The {@code standard} methods and any collection views they return are not guaranteed to be
047 * thread-safe, even when all of the methods that they depend on are thread-safe.
048 *
049 * @author Mike Bostock
050 * @author Louis Wasserman
051 * @since 2.0
052 */
053@GwtCompatible
054public abstract class ForwardingList<E extends @Nullable Object> extends ForwardingCollection<E>
055    implements List<E> {
056  // TODO(lowasser): identify places where thread safety is actually lost
057
058  /** Constructor for use by subclasses. */
059  protected ForwardingList() {}
060
061  @Override
062  protected abstract List<E> delegate();
063
064  @Override
065  public void add(int index, @ParametricNullness E element) {
066    delegate().add(index, element);
067  }
068
069  @CanIgnoreReturnValue
070  @Override
071  public boolean addAll(int index, Collection<? extends E> elements) {
072    return delegate().addAll(index, elements);
073  }
074
075  @Override
076  @ParametricNullness
077  public E get(int index) {
078    return delegate().get(index);
079  }
080
081  @Override
082  public int indexOf(@CheckForNull Object element) {
083    return delegate().indexOf(element);
084  }
085
086  @Override
087  public int lastIndexOf(@CheckForNull Object element) {
088    return delegate().lastIndexOf(element);
089  }
090
091  @Override
092  public ListIterator<E> listIterator() {
093    return delegate().listIterator();
094  }
095
096  @Override
097  public ListIterator<E> listIterator(int index) {
098    return delegate().listIterator(index);
099  }
100
101  @CanIgnoreReturnValue
102  @Override
103  @ParametricNullness
104  public E remove(int index) {
105    return delegate().remove(index);
106  }
107
108  @CanIgnoreReturnValue
109  @Override
110  @ParametricNullness
111  public E set(int index, @ParametricNullness E element) {
112    return delegate().set(index, element);
113  }
114
115  @Override
116  public List<E> subList(int fromIndex, int toIndex) {
117    return delegate().subList(fromIndex, toIndex);
118  }
119
120  @Override
121  public boolean equals(@CheckForNull Object object) {
122    return object == this || delegate().equals(object);
123  }
124
125  @Override
126  public int hashCode() {
127    return delegate().hashCode();
128  }
129
130  /**
131   * A sensible default implementation of {@link #add(Object)}, in terms of {@link #add(int,
132   * Object)}. If you override {@link #add(int, Object)}, you may wish to override {@link
133   * #add(Object)} to forward to this implementation.
134   *
135   * @since 7.0
136   */
137  protected boolean standardAdd(@ParametricNullness E element) {
138    add(size(), element);
139    return true;
140  }
141
142  /**
143   * A sensible default implementation of {@link #addAll(int, Collection)}, in terms of the {@code
144   * add} method of {@link #listIterator(int)}. If you override {@link #listIterator(int)}, you may
145   * wish to override {@link #addAll(int, Collection)} to forward to this implementation.
146   *
147   * @since 7.0
148   */
149  protected boolean standardAddAll(int index, Iterable<? extends E> elements) {
150    return Lists.addAllImpl(this, index, elements);
151  }
152
153  /**
154   * A sensible default implementation of {@link #indexOf}, in terms of {@link #listIterator()}. If
155   * you override {@link #listIterator()}, you may wish to override {@link #indexOf} to forward to
156   * this implementation.
157   *
158   * @since 7.0
159   */
160  protected int standardIndexOf(@CheckForNull Object element) {
161    return Lists.indexOfImpl(this, element);
162  }
163
164  /**
165   * A sensible default implementation of {@link #lastIndexOf}, in terms of {@link
166   * #listIterator(int)}. If you override {@link #listIterator(int)}, you may wish to override
167   * {@link #lastIndexOf} to forward to this implementation.
168   *
169   * @since 7.0
170   */
171  protected int standardLastIndexOf(@CheckForNull Object element) {
172    return Lists.lastIndexOfImpl(this, element);
173  }
174
175  /**
176   * A sensible default implementation of {@link #iterator}, in terms of {@link #listIterator()}. If
177   * you override {@link #listIterator()}, you may wish to override {@link #iterator} to forward to
178   * this implementation.
179   *
180   * @since 7.0
181   */
182  protected Iterator<E> standardIterator() {
183    return listIterator();
184  }
185
186  /**
187   * A sensible default implementation of {@link #listIterator()}, in terms of {@link
188   * #listIterator(int)}. If you override {@link #listIterator(int)}, you may wish to override
189   * {@link #listIterator()} to forward to this implementation.
190   *
191   * @since 7.0
192   */
193  protected ListIterator<E> standardListIterator() {
194    return listIterator(0);
195  }
196
197  /**
198   * A sensible default implementation of {@link #listIterator(int)}, in terms of {@link #size},
199   * {@link #get(int)}, {@link #set(int, Object)}, {@link #add(int, Object)}, and {@link
200   * #remove(int)}. If you override any of these methods, you may wish to override {@link
201   * #listIterator(int)} to forward to this implementation.
202   *
203   * @since 7.0
204   */
205  protected ListIterator<E> standardListIterator(int start) {
206    return Lists.listIteratorImpl(this, start);
207  }
208
209  /**
210   * A sensible default implementation of {@link #subList(int, int)}. If you override any other
211   * methods, you may wish to override {@link #subList(int, int)} to forward to this implementation.
212   *
213   * @since 7.0
214   */
215  protected List<E> standardSubList(int fromIndex, int toIndex) {
216    return Lists.subListImpl(this, fromIndex, toIndex);
217  }
218
219  /**
220   * A sensible definition of {@link #equals(Object)} in terms of {@link #size} and {@link
221   * #iterator}. If you override either of those methods, you may wish to override {@link
222   * #equals(Object)} to forward to this implementation.
223   *
224   * @since 7.0
225   */
226  protected boolean standardEquals(@CheckForNull Object object) {
227    return Lists.equalsImpl(this, object);
228  }
229
230  /**
231   * A sensible definition of {@link #hashCode} in terms of {@link #iterator}. If you override
232   * {@link #iterator}, you may wish to override {@link #hashCode} to forward to this
233   * implementation.
234   *
235   * @since 7.0
236   */
237  protected int standardHashCode() {
238    return Lists.hashCodeImpl(this);
239  }
240}