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