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.Beta;
020import com.google.common.annotations.GwtCompatible;
021import com.google.common.base.Objects;
022
023import java.util.Collection;
024import java.util.Iterator;
025
026import 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
049public 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}