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
017 package com.google.common.collect;
018
019 import com.google.common.annotations.Beta;
020 import com.google.common.annotations.GwtCompatible;
021 import com.google.common.base.Objects;
022
023 import java.util.Collection;
024 import java.util.Iterator;
025
026 import javax.annotation.Nullable;
027
028 /**
029 * A collection which forwards all its method calls to another collection.
030 * Subclasses should override one or more methods to modify the behavior of the
031 * backing collection as desired per the <a
032 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
033 *
034 * <p><b>Warning:</b> The methods of {@code ForwardingCollection} forward
035 * <b>indiscriminately</b> to the methods of the delegate. For example,
036 * overriding {@link #add} alone <b>will not</b> change the behavior of {@link
037 * #addAll}, which can lead to unexpected behavior. In this case, you should
038 * override {@code addAll} as well, either providing your own implementation, or
039 * delegating to the provided {@code standardAddAll} method.
040 *
041 * <p>The {@code standard} methods are not guaranteed to be thread-safe, even
042 * when all of the methods that they depend on are thread-safe.
043 *
044 * @author Kevin Bourrillion
045 * @author Louis Wasserman
046 * @since 2 (imported from Google Collections Library)
047 */
048 @GwtCompatible
049 public abstract class ForwardingCollection<E> extends ForwardingObject
050 implements Collection<E> {
051 // TODO(user): identify places where thread safety is actually lost
052
053 /** Constructor for use by subclasses. */
054 protected ForwardingCollection() {}
055
056 @Override protected abstract Collection<E> delegate();
057
058 @Override
059 public Iterator<E> iterator() {
060 return delegate().iterator();
061 }
062
063 @Override
064 public int size() {
065 return delegate().size();
066 }
067
068 @Override
069 public boolean removeAll(Collection<?> collection) {
070 return delegate().removeAll(collection);
071 }
072
073 @Override
074 public boolean isEmpty() {
075 return delegate().isEmpty();
076 }
077
078 @Override
079 public boolean contains(Object object) {
080 return delegate().contains(object);
081 }
082
083 @Override
084 public boolean add(E element) {
085 return delegate().add(element);
086 }
087
088 @Override
089 public boolean remove(Object object) {
090 return delegate().remove(object);
091 }
092
093 @Override
094 public boolean containsAll(Collection<?> collection) {
095 return delegate().containsAll(collection);
096 }
097
098 @Override
099 public boolean addAll(Collection<? extends E> collection) {
100 return delegate().addAll(collection);
101 }
102
103 @Override
104 public boolean retainAll(Collection<?> collection) {
105 return delegate().retainAll(collection);
106 }
107
108 @Override
109 public void clear() {
110 delegate().clear();
111 }
112
113 @Override
114 public Object[] toArray() {
115 return delegate().toArray();
116 }
117
118 @Override
119 public <T> T[] toArray(T[] array) {
120 return delegate().toArray(array);
121 }
122
123 /**
124 * A sensible definition of {@link #contains} in terms of {@link #iterator}.
125 * If you override {@link #iterator}, you may wish to override {@link
126 * #contains} to forward to this implementation.
127 *
128 * @since 7
129 */
130 @Beta protected boolean standardContains(@Nullable Object object) {
131 return Iterators.contains(iterator(), object);
132 }
133
134 /**
135 * A sensible definition of {@link #containsAll} in terms of {@link #contains}
136 * . If you override {@link #contains}, you may wish to override {@link
137 * #containsAll} to forward to this implementation.
138 *
139 * @since 7
140 */
141 @Beta protected boolean standardContainsAll(Collection<?> collection) {
142 for (Object o : collection) {
143 if (!contains(o)) {
144 return false;
145 }
146 }
147 return true;
148 }
149
150 /**
151 * A sensible definition of {@link #addAll} in terms of {@link #add}. If you
152 * override {@link #add}, you may wish to override {@link #addAll} to forward
153 * to this implementation.
154 *
155 * @since 7
156 */
157 @Beta 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},
163 * using the iterator's {@code remove} method. If you override {@link
164 * #iterator}, you may wish to override {@link #remove} to forward to this
165 * implementation.
166 *
167 * @since 7
168 */
169 @Beta protected boolean standardRemove(@Nullable Object object) {
170 Iterator<E> iterator = iterator();
171 while (iterator.hasNext()) {
172 if (Objects.equal(iterator.next(), object)) {
173 iterator.remove();
174 return true;
175 }
176 }
177 return false;
178 }
179
180 /**
181 * A sensible definition of {@link #removeAll} in terms of {@link #iterator},
182 * using the iterator's {@code remove} method. If you override {@link
183 * #iterator}, you may wish to override {@link #removeAll} to forward to this
184 * implementation.
185 *
186 * @since 7
187 */
188 @Beta protected boolean standardRemoveAll(Collection<?> collection) {
189 return Iterators.removeAll(iterator(), collection);
190 }
191
192 /**
193 * A sensible definition of {@link #retainAll} in terms of {@link #iterator},
194 * using the iterator's {@code remove} method. If you override {@link
195 * #iterator}, you may wish to override {@link #retainAll} to forward to this
196 * implementation.
197 *
198 * @since 7
199 */
200 @Beta protected boolean standardRetainAll(Collection<?> collection) {
201 return Iterators.retainAll(iterator(), collection);
202 }
203
204 /**
205 * A sensible definition of {@link #clear} in terms of {@link #iterator},
206 * using the iterator's {@code remove} method. If you override {@link
207 * #iterator}, you may wish to override {@link #clear} to forward to this
208 * implementation.
209 *
210 * @since 7
211 */
212 @Beta protected void standardClear() {
213 Iterator<E> iterator = iterator();
214 while (iterator.hasNext()) {
215 iterator.next();
216 iterator.remove();
217 }
218 }
219
220 /**
221 * A sensible definition of {@link #isEmpty} as {@code !iterator().hasNext}.
222 * If you override {@link #isEmpty}, you may wish to override {@link #isEmpty}
223 * to forward to this implementation. Alternately, it may be more efficient to
224 * implement {@code isEmpty} as {@code size() == 0}.
225 *
226 * @since 7
227 */
228 @Beta protected boolean standardIsEmpty() {
229 return !iterator().hasNext();
230 }
231
232 /**
233 * A sensible definition of {@link #toString} in terms of {@link #iterator}.
234 * If you override {@link #iterator}, you may wish to override {@link
235 * #toString} to forward to this implementation.
236 *
237 * @since 7
238 */
239 @Beta protected String standardToString() {
240 return Collections2.toStringImpl(this);
241 }
242
243 /**
244 * A sensible definition of {@link #toArray()} in terms of {@link
245 * #toArray(Object[])}. If you override {@link #toArray(Object[])}, you may
246 * wish to override {@link #toArray} to forward to this implementation.
247 *
248 * @since 7
249 */
250 @Beta protected Object[] standardToArray() {
251 Object[] newArray = new Object[size()];
252 return toArray(newArray);
253 }
254
255 /**
256 * A sensible definition of {@link #toArray(Object[])} in terms of {@link
257 * #size} and {@link #iterator}. If you override either of these methods, you
258 * may wish to override {@link #toArray} to forward to this implementation.
259 *
260 * @since 7
261 */
262 @Beta protected <T> T[] standardToArray(T[] array) {
263 return ObjectArrays.toArrayImpl(this, array);
264 }
265 }