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 static com.google.common.base.Preconditions.checkNotNull;
20  
21  import com.google.common.annotations.GwtCompatible;
22  
23  import java.util.Collection;
24  import java.util.Set;
25  
26  import javax.annotation.Nullable;
27  
28  /**
29   * A set which forwards all its method calls to another set. Subclasses should
30   * override one or more methods to modify the behavior of the backing set as
31   * desired per the <a
32   * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
33   *
34   * <p><b>Warning:</b> The methods of {@code ForwardingSet} forward
35   * <b>indiscriminately</b> to the methods of the delegate. For example,
36   * overriding {@link #add} alone <b>will not</b> change the behavior of {@link
37   * #addAll}, which can lead to unexpected behavior. In this case, you should
38   * override {@code addAll} as well, either providing your own implementation, or
39   * delegating to the provided {@code standardAddAll} method.
40   *
41   * <p>The {@code standard} methods are not guaranteed to be thread-safe, even
42   * when all of the methods that they depend on are thread-safe.
43   *
44   * @author Kevin Bourrillion
45   * @author Louis Wasserman
46   * @since 2.0 (imported from Google Collections Library)
47   */
48  @GwtCompatible
49  public abstract class ForwardingSet<E> extends ForwardingCollection<E>
50      implements Set<E> {
51    // TODO(user): identify places where thread safety is actually lost
52  
53    /** Constructor for use by subclasses. */
54    protected ForwardingSet() {}
55  
56    @Override protected abstract Set<E> delegate();
57  
58    @Override public boolean equals(@Nullable Object object) {
59      return object == this || delegate().equals(object);
60    }
61  
62    @Override public int hashCode() {
63      return delegate().hashCode();
64    }
65  
66    /**
67     * A sensible definition of {@link #removeAll} in terms of {@link #iterator}
68     * and {@link #remove}.  If you override {@code iterator} or {@code remove},
69     * you may wish to override {@link #removeAll} to forward to this
70     * implementation.
71     *
72     * @since 7.0 (this version overrides the {@code ForwardingCollection} version as of 12.0)
73     */
74    @Override
75    protected boolean standardRemoveAll(Collection<?> collection) {
76      return Sets.removeAllImpl(this, checkNotNull(collection)); // for GWT
77    }
78  
79    /**
80     * A sensible definition of {@link #equals} in terms of {@link #size} and
81     * {@link #containsAll}. If you override either of those methods, you may wish
82     * to override {@link #equals} to forward to this implementation.
83     *
84     * @since 7.0
85     */
86    protected boolean standardEquals(@Nullable Object object) {
87      return Sets.equalsImpl(this, object);
88    }
89  
90    /**
91     * A sensible definition of {@link #hashCode} in terms of {@link #iterator}.
92     * If you override {@link #iterator}, you may wish to override {@link #equals}
93     * to forward to this implementation.
94     *
95     * @since 7.0
96     */
97    protected int standardHashCode() {
98      return Sets.hashCodeImpl(this);
99    }
100 }