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
17 package com.google.common.collect;
18
19 import com.google.common.annotations.Beta;
20 import com.google.common.annotations.GwtCompatible;
21 import com.google.errorprone.annotations.CanIgnoreReturnValue;
22 import java.util.Collection;
23 import java.util.Iterator;
24 import java.util.List;
25 import java.util.ListIterator;
26 import org.checkerframework.checker.nullness.qual.Nullable;
27
28 /**
29 * A list which forwards all its method calls to another list. Subclasses should override one or
30 * more methods to modify the behavior of the backing list as desired per the <a
31 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
32 *
33 * <p>This class does not implement {@link java.util.RandomAccess}. If the delegate supports random
34 * access, the {@code ForwardingList} subclass should implement the {@code RandomAccess} interface.
35 *
36 * <p><b>Warning:</b> The methods of {@code ForwardingList} forward <b>indiscriminately</b> to the
37 * methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change the
38 * behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should
39 * override {@code addAll} as well, either providing your own implementation, or delegating to the
40 * provided {@code standardAddAll} method.
41 *
42 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
43 * default} methods. Instead, it inherits their default implementations. When those implementations
44 * invoke methods, they invoke methods on the {@code ForwardingList}.
45 *
46 * <p>The {@code standard} methods and any collection views they return are not guaranteed to be
47 * thread-safe, even when all of the methods that they depend on are thread-safe.
48 *
49 * @author Mike Bostock
50 * @author Louis Wasserman
51 * @since 2.0
52 */
53 @GwtCompatible
54 public abstract class ForwardingList<E> extends ForwardingCollection<E> implements List<E> {
55 // TODO(lowasser): identify places where thread safety is actually lost
56
57 /** Constructor for use by subclasses. */
58 protected ForwardingList() {}
59
60 @Override
61 protected abstract List<E> delegate();
62
63 @Override
64 public void add(int index, E element) {
65 delegate().add(index, element);
66 }
67
68 @CanIgnoreReturnValue
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 @CanIgnoreReturnValue
100 @Override
101 public E remove(int index) {
102 return delegate().remove(index);
103 }
104
105 @CanIgnoreReturnValue
106 @Override
107 public E set(int index, E element) {
108 return delegate().set(index, element);
109 }
110
111 @Override
112 public List<E> subList(int fromIndex, int toIndex) {
113 return delegate().subList(fromIndex, toIndex);
114 }
115
116 @Override
117 public boolean equals(@Nullable Object object) {
118 return object == this || delegate().equals(object);
119 }
120
121 @Override
122 public int hashCode() {
123 return delegate().hashCode();
124 }
125
126 /**
127 * A sensible default implementation of {@link #add(Object)}, in terms of {@link #add(int,
128 * Object)}. If you override {@link #add(int, Object)}, you may wish to override {@link
129 * #add(Object)} to forward to this implementation.
130 *
131 * @since 7.0
132 */
133 protected boolean standardAdd(E element) {
134 add(size(), element);
135 return true;
136 }
137
138 /**
139 * A sensible default implementation of {@link #addAll(int, Collection)}, in terms of the {@code
140 * add} method of {@link #listIterator(int)}. If you override {@link #listIterator(int)}, you may
141 * wish to override {@link #addAll(int, Collection)} to forward to this implementation.
142 *
143 * @since 7.0
144 */
145 protected boolean standardAddAll(int index, Iterable<? extends E> elements) {
146 return Lists.addAllImpl(this, index, elements);
147 }
148
149 /**
150 * A sensible default implementation of {@link #indexOf}, in terms of {@link #listIterator()}. If
151 * you override {@link #listIterator()}, you may wish to override {@link #indexOf} to forward to
152 * this implementation.
153 *
154 * @since 7.0
155 */
156 protected int standardIndexOf(@Nullable Object element) {
157 return Lists.indexOfImpl(this, element);
158 }
159
160 /**
161 * A sensible default implementation of {@link #lastIndexOf}, in terms of {@link
162 * #listIterator(int)}. If you override {@link #listIterator(int)}, you may wish to override
163 * {@link #lastIndexOf} to forward to this 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 {@link #listIterator()}. If
173 * you override {@link #listIterator()}, you may wish to override {@link #iterator} to forward to
174 * 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 {@link
184 * #listIterator(int)}. If you override {@link #listIterator(int)}, you may wish to override
185 * {@link #listIterator()} to forward to this implementation.
186 *
187 * @since 7.0
188 */
189 protected ListIterator<E> standardListIterator() {
190 return listIterator(0);
191 }
192
193 /**
194 * A sensible default implementation of {@link #listIterator(int)}, in terms of {@link #size},
195 * {@link #get(int)}, {@link #set(int, Object)}, {@link #add(int, Object)}, and {@link
196 * #remove(int)}. If you override any of these methods, you may wish to override {@link
197 * #listIterator(int)} to forward to this implementation.
198 *
199 * @since 7.0
200 */
201 @Beta
202 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 override any other
208 * methods, you may wish to override {@link #subList(int, int)} to forward to this implementation.
209 *
210 * @since 7.0
211 */
212 @Beta
213 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} and {@link
219 * #iterator}. If you override either of those methods, you may wish to override {@link
220 * #equals(Object)} to forward to this implementation.
221 *
222 * @since 7.0
223 */
224 @Beta
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 @Beta
237 protected int standardHashCode() {
238 return Lists.hashCodeImpl(this);
239 }
240 }