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.GwtCompatible;
20 import com.google.common.base.Objects;
21 import com.google.errorprone.annotations.CanIgnoreReturnValue;
22 import java.util.Collection;
23 import java.util.Iterator;
24 import org.checkerframework.checker.nullness.qual.Nullable;
25
26 /**
27 * A collection which forwards all its method calls to another collection. Subclasses should
28 * override one or more methods to modify the behavior of the backing collection as desired per the
29 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
30 *
31 * <p><b>Warning:</b> The methods of {@code ForwardingCollection} forward <b>indiscriminately</b> to
32 * the methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change
33 * the behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should
34 * override {@code addAll} as well, either providing your own implementation, or delegating to the
35 * provided {@code standardAddAll} method.
36 *
37 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
38 * default} methods. Instead, it inherits their default implementations. When those implementations
39 * invoke methods, they invoke methods on the {@code ForwardingCollection}.
40 *
41 * <p>The {@code standard} methods are not guaranteed to be thread-safe, even when all of the
42 * methods that they depend on are thread-safe.
43 *
44 * @author Kevin Bourrillion
45 * @author Louis Wasserman
46 * @since 2.0
47 */
48 @GwtCompatible
49 public abstract class ForwardingCollection<E> extends ForwardingObject implements Collection<E> {
50 // TODO(lowasser): identify places where thread safety is actually lost
51
52 /** Constructor for use by subclasses. */
53 protected ForwardingCollection() {}
54
55 @Override
56 protected abstract Collection<E> delegate();
57
58 @Override
59 public Iterator<E> iterator() {
60 return delegate().iterator();
61 }
62
63 @Override
64 public int size() {
65 return delegate().size();
66 }
67
68 @CanIgnoreReturnValue
69 @Override
70 public boolean removeAll(Collection<?> collection) {
71 return delegate().removeAll(collection);
72 }
73
74 @Override
75 public boolean isEmpty() {
76 return delegate().isEmpty();
77 }
78
79 @Override
80 public boolean contains(Object object) {
81 return delegate().contains(object);
82 }
83
84 @CanIgnoreReturnValue
85 @Override
86 public boolean add(E element) {
87 return delegate().add(element);
88 }
89
90 @CanIgnoreReturnValue
91 @Override
92 public boolean remove(Object object) {
93 return delegate().remove(object);
94 }
95
96 @Override
97 public boolean containsAll(Collection<?> collection) {
98 return delegate().containsAll(collection);
99 }
100
101 @CanIgnoreReturnValue
102 @Override
103 public boolean addAll(Collection<? extends E> collection) {
104 return delegate().addAll(collection);
105 }
106
107 @CanIgnoreReturnValue
108 @Override
109 public boolean retainAll(Collection<?> collection) {
110 return delegate().retainAll(collection);
111 }
112
113 @Override
114 public void clear() {
115 delegate().clear();
116 }
117
118 @Override
119 public Object[] toArray() {
120 return delegate().toArray();
121 }
122
123 @CanIgnoreReturnValue
124 @Override
125 public <T> T[] toArray(T[] array) {
126 return delegate().toArray(array);
127 }
128
129 /**
130 * A sensible definition of {@link #contains} in terms of {@link #iterator}. If you override
131 * {@link #iterator}, you may wish to override {@link #contains} to forward to this
132 * implementation.
133 *
134 * @since 7.0
135 */
136 protected boolean standardContains(@Nullable Object object) {
137 return Iterators.contains(iterator(), object);
138 }
139
140 /**
141 * A sensible definition of {@link #containsAll} in terms of {@link #contains} . If you override
142 * {@link #contains}, you may wish to override {@link #containsAll} to forward to this
143 * implementation.
144 *
145 * @since 7.0
146 */
147 protected boolean standardContainsAll(Collection<?> collection) {
148 return Collections2.containsAllImpl(this, collection);
149 }
150
151 /**
152 * A sensible definition of {@link #addAll} in terms of {@link #add}. If you override {@link
153 * #add}, you may wish to override {@link #addAll} to forward to this implementation.
154 *
155 * @since 7.0
156 */
157 protected boolean standardAddAll(Collection<? extends E> collection) {
158 return Iterators.addAll(this, collection.iterator());
159 }
160
161 /**
162 * A sensible definition of {@link #remove} in terms of {@link #iterator}, using the iterator's
163 * {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
164 * #remove} to forward to this implementation.
165 *
166 * @since 7.0
167 */
168 protected boolean standardRemove(@Nullable Object object) {
169 Iterator<E> iterator = iterator();
170 while (iterator.hasNext()) {
171 if (Objects.equal(iterator.next(), object)) {
172 iterator.remove();
173 return true;
174 }
175 }
176 return false;
177 }
178
179 /**
180 * A sensible definition of {@link #removeAll} in terms of {@link #iterator}, using the iterator's
181 * {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
182 * #removeAll} to forward to this implementation.
183 *
184 * @since 7.0
185 */
186 protected boolean standardRemoveAll(Collection<?> collection) {
187 return Iterators.removeAll(iterator(), collection);
188 }
189
190 /**
191 * A sensible definition of {@link #retainAll} in terms of {@link #iterator}, using the iterator's
192 * {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
193 * #retainAll} to forward to this implementation.
194 *
195 * @since 7.0
196 */
197 protected boolean standardRetainAll(Collection<?> collection) {
198 return Iterators.retainAll(iterator(), collection);
199 }
200
201 /**
202 * A sensible definition of {@link #clear} in terms of {@link #iterator}, using the iterator's
203 * {@code remove} method. If you override {@link #iterator}, you may wish to override {@link
204 * #clear} to forward to this implementation.
205 *
206 * @since 7.0
207 */
208 protected void standardClear() {
209 Iterators.clear(iterator());
210 }
211
212 /**
213 * A sensible definition of {@link #isEmpty} as {@code !iterator().hasNext}. If you override
214 * {@link #isEmpty}, you may wish to override {@link #isEmpty} to forward to this implementation.
215 * Alternately, it may be more efficient to implement {@code isEmpty} as {@code size() == 0}.
216 *
217 * @since 7.0
218 */
219 protected boolean standardIsEmpty() {
220 return !iterator().hasNext();
221 }
222
223 /**
224 * A sensible definition of {@link #toString} in terms of {@link #iterator}. If you override
225 * {@link #iterator}, you may wish to override {@link #toString} to forward to this
226 * implementation.
227 *
228 * @since 7.0
229 */
230 protected String standardToString() {
231 return Collections2.toStringImpl(this);
232 }
233
234 /**
235 * A sensible definition of {@link #toArray()} in terms of {@link #toArray(Object[])}. If you
236 * override {@link #toArray(Object[])}, you may wish to override {@link #toArray} to forward to
237 * this implementation.
238 *
239 * @since 7.0
240 */
241 protected Object[] standardToArray() {
242 Object[] newArray = new Object[size()];
243 return toArray(newArray);
244 }
245
246 /**
247 * A sensible definition of {@link #toArray(Object[])} in terms of {@link #size} and {@link
248 * #iterator}. If you override either of these methods, you may wish to override {@link #toArray}
249 * to forward to this implementation.
250 *
251 * @since 7.0
252 */
253 protected <T> T[] standardToArray(T[] array) {
254 return ObjectArrays.toArrayImpl(this, array);
255 }
256 }