1/*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.collect;
18
19import com.google.common.annotations.Beta;
20import com.google.common.annotations.GwtCompatible;
21
22import java.util.Collection;
23import java.util.Iterator;
24import java.util.List;
25import java.util.ListIterator;
26
27import javax.annotation.Nullable;
28
29/**
30 * A list which forwards all its method calls to another list. Subclasses should
31 * override one or more methods to modify the behavior of the backing list as
32 * desired per the <a
33 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
34 *
35 * <p>This class does not implement {@link java.util.RandomAccess}. If the
36 * delegate supports random access, the {@code ForwardingList} subclass should
37 * implement the {@code RandomAccess} interface.
38 *
39 * <p><b>Warning:</b> The methods of {@code ForwardingList} forward
40 * <b>indiscriminately</b> to the methods of the delegate. For example,
41 * overriding {@link #add} alone <b>will not</b> change the behavior of {@link
42 * #addAll}, which can lead to unexpected behavior. In this case, you should
43 * override {@code addAll} as well, either providing your own implementation, or
44 * delegating to the provided {@code standardAddAll} method.
45 *
46 * <p>The {@code standard} methods and any collection views they return are not
47 * guaranteed to be thread-safe, even when all of the methods that they depend
48 * on are thread-safe.
49 *
50 * @author Mike Bostock
51 * @author Louis Wasserman
52 * @since 2.0 (imported from Google Collections Library)
53 */
54@GwtCompatible
55public abstract class ForwardingList<E> extends ForwardingCollection<E>
56    implements List<E> {
57  // TODO(user): identify places where thread safety is actually lost
58
59  /** Constructor for use by subclasses. */
60  protected ForwardingList() {}
61
62  @Override protected abstract List<E> delegate();
63
64  @Override
65  public void add(int index, E element) {
66    delegate().add(index, element);
67  }
68
69  @Override
70  public boolean addAll(int index, Collection<? extends E> elements) {
71    return delegate().addAll(index, elements);
72  }
73
74  @Override
75  public E get(int index) {
76    return delegate().get(index);
77  }
78
79  @Override
80  public int indexOf(Object element) {
81    return delegate().indexOf(element);
82  }
83
84  @Override
85  public int lastIndexOf(Object element) {
86    return delegate().lastIndexOf(element);
87  }
88
89  @Override
90  public ListIterator<E> listIterator() {
91    return delegate().listIterator();
92  }
93
94  @Override
95  public ListIterator<E> listIterator(int index) {
96    return delegate().listIterator(index);
97  }
98
99  @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}
239