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.GwtCompatible;
020import com.google.common.base.Objects;
021
022import java.util.Collection;
023import java.util.Iterator;
024
025import javax.annotation.Nullable;
026
027/**
028 * A collection which forwards all its method calls to another collection.
029 * Subclasses should override one or more methods to modify the behavior of the
030 * backing collection as desired per the <a
031 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
032 *
033 * <p><b>Warning:</b> The methods of {@code ForwardingCollection} forward
034 * <b>indiscriminately</b> to the methods of the delegate. For example,
035 * overriding {@link #add} alone <b>will not</b> change the behavior of {@link
036 * #addAll}, which can lead to unexpected behavior. In this case, you should
037 * override {@code addAll} as well, either providing your own implementation, or
038 * delegating to the provided {@code standardAddAll} method.
039 *
040 * <p>The {@code standard} methods are not guaranteed to be thread-safe, even
041 * when all of the methods that they depend on are thread-safe.
042 *
043 * @author Kevin Bourrillion
044 * @author Louis Wasserman
045 * @since 2.0
046 */
047@GwtCompatible
048public abstract class ForwardingCollection<E> extends ForwardingObject implements Collection<E> {
049  // TODO(lowasser): identify places where thread safety is actually lost
050
051  /** Constructor for use by subclasses. */
052  protected ForwardingCollection() {}
053
054  @Override
055  protected abstract Collection<E> delegate();
056
057  @Override
058  public Iterator<E> iterator() {
059    return delegate().iterator();
060  }
061
062  @Override
063  public int size() {
064    return delegate().size();
065  }
066
067  @Override
068  public boolean removeAll(Collection<?> collection) {
069    return delegate().removeAll(collection);
070  }
071
072  @Override
073  public boolean isEmpty() {
074    return delegate().isEmpty();
075  }
076
077  @Override
078  public boolean contains(Object object) {
079    return delegate().contains(object);
080  }
081
082  @Override
083  public boolean add(E element) {
084    return delegate().add(element);
085  }
086
087  @Override
088  public boolean remove(Object object) {
089    return delegate().remove(object);
090  }
091
092  @Override
093  public boolean containsAll(Collection<?> collection) {
094    return delegate().containsAll(collection);
095  }
096
097  @Override
098  public boolean addAll(Collection<? extends E> collection) {
099    return delegate().addAll(collection);
100  }
101
102  @Override
103  public boolean retainAll(Collection<?> collection) {
104    return delegate().retainAll(collection);
105  }
106
107  @Override
108  public void clear() {
109    delegate().clear();
110  }
111
112  @Override
113  public Object[] toArray() {
114    return delegate().toArray();
115  }
116
117  @Override
118  public <T> T[] toArray(T[] array) {
119    return delegate().toArray(array);
120  }
121
122  /**
123   * A sensible definition of {@link #contains} in terms of {@link #iterator}.
124   * If you override {@link #iterator}, you may wish to override {@link
125   * #contains} to forward to this implementation.
126   *
127   * @since 7.0
128   */
129  protected boolean standardContains(@Nullable Object object) {
130    return Iterators.contains(iterator(), object);
131  }
132
133  /**
134   * A sensible definition of {@link #containsAll} in terms of {@link #contains}
135   * . If you override {@link #contains}, you may wish to override {@link
136   * #containsAll} to forward to this implementation.
137   *
138   * @since 7.0
139   */
140  protected boolean standardContainsAll(Collection<?> collection) {
141    return Collections2.containsAllImpl(this, collection);
142  }
143
144  /**
145   * A sensible definition of {@link #addAll} in terms of {@link #add}. If you
146   * override {@link #add}, you may wish to override {@link #addAll} to forward
147   * to this implementation.
148   *
149   * @since 7.0
150   */
151  protected boolean standardAddAll(Collection<? extends E> collection) {
152    return Iterators.addAll(this, collection.iterator());
153  }
154
155  /**
156   * A sensible definition of {@link #remove} in terms of {@link #iterator},
157   * using the iterator's {@code remove} method. If you override {@link
158   * #iterator}, you may wish to override {@link #remove} to forward to this
159   * implementation.
160   *
161   * @since 7.0
162   */
163  protected boolean standardRemove(@Nullable Object object) {
164    Iterator<E> iterator = iterator();
165    while (iterator.hasNext()) {
166      if (Objects.equal(iterator.next(), object)) {
167        iterator.remove();
168        return true;
169      }
170    }
171    return false;
172  }
173
174  /**
175   * A sensible definition of {@link #removeAll} in terms of {@link #iterator},
176   * using the iterator's {@code remove} method. If you override {@link
177   * #iterator}, you may wish to override {@link #removeAll} to forward to this
178   * implementation.
179   *
180   * @since 7.0
181   */
182  protected boolean standardRemoveAll(Collection<?> collection) {
183    return Iterators.removeAll(iterator(), collection);
184  }
185
186  /**
187   * A sensible definition of {@link #retainAll} in terms of {@link #iterator},
188   * using the iterator's {@code remove} method. If you override {@link
189   * #iterator}, you may wish to override {@link #retainAll} to forward to this
190   * implementation.
191   *
192   * @since 7.0
193   */
194  protected boolean standardRetainAll(Collection<?> collection) {
195    return Iterators.retainAll(iterator(), collection);
196  }
197
198  /**
199   * A sensible definition of {@link #clear} in terms of {@link #iterator},
200   * using the iterator's {@code remove} method. If you override {@link
201   * #iterator}, you may wish to override {@link #clear} to forward to this
202   * implementation.
203   *
204   * @since 7.0
205   */
206  protected void standardClear() {
207    Iterators.clear(iterator());
208  }
209
210  /**
211   * A sensible definition of {@link #isEmpty} as {@code !iterator().hasNext}.
212   * If you override {@link #isEmpty}, you may wish to override {@link #isEmpty}
213   * to forward to this implementation. Alternately, it may be more efficient to
214   * implement {@code isEmpty} as {@code size() == 0}.
215   *
216   * @since 7.0
217   */
218  protected boolean standardIsEmpty() {
219    return !iterator().hasNext();
220  }
221
222  /**
223   * A sensible definition of {@link #toString} in terms of {@link #iterator}.
224   * If you override {@link #iterator}, you may wish to override {@link
225   * #toString} to forward to this implementation.
226   *
227   * @since 7.0
228   */
229  protected String standardToString() {
230    return Collections2.toStringImpl(this);
231  }
232
233  /**
234   * A sensible definition of {@link #toArray()} in terms of {@link
235   * #toArray(Object[])}. If you override {@link #toArray(Object[])}, you may
236   * wish to override {@link #toArray} to forward to this implementation.
237   *
238   * @since 7.0
239   */
240  protected Object[] standardToArray() {
241    Object[] newArray = new Object[size()];
242    return toArray(newArray);
243  }
244
245  /**
246   * A sensible definition of {@link #toArray(Object[])} in terms of {@link
247   * #size} and {@link #iterator}. If you override either of these methods, you
248   * may wish to override {@link #toArray} to forward to this implementation.
249   *
250   * @since 7.0
251   */
252  protected <T> T[] standardToArray(T[] array) {
253    return ObjectArrays.toArrayImpl(this, array);
254  }
255}