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 import java.util.Collection;
23 import java.util.Set;
24 import org.checkerframework.checker.nullness.qual.Nullable;
25
26 /**
27 * A set which forwards all its method calls to another set. Subclasses should override one or more
28 * methods to modify the behavior of the backing set as desired per the <a
29 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
30 *
31 * <p><b>Warning:</b> The methods of {@code ForwardingSet} forward <b>indiscriminately</b> to the
32 * methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change the
33 * 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 ForwardingSet}.
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 ForwardingSet<E> extends ForwardingCollection<E> implements Set<E> {
50 // TODO(lowasser): identify places where thread safety is actually lost
51
52 /** Constructor for use by subclasses. */
53 protected ForwardingSet() {}
54
55 @Override
56 protected abstract Set<E> delegate();
57
58 @Override
59 public boolean equals(@Nullable Object object) {
60 return object == this || delegate().equals(object);
61 }
62
63 @Override
64 public int hashCode() {
65 return delegate().hashCode();
66 }
67
68 /**
69 * A sensible definition of {@link #removeAll} in terms of {@link #iterator} and {@link #remove}.
70 * If you override {@code iterator} or {@code remove}, you may wish to override {@link #removeAll}
71 * to forward to this implementation.
72 *
73 * @since 7.0 (this version overrides the {@code ForwardingCollection} version as of 12.0)
74 */
75 @Override
76 protected boolean standardRemoveAll(Collection<?> collection) {
77 return Sets.removeAllImpl(this, checkNotNull(collection)); // for GWT
78 }
79
80 /**
81 * A sensible definition of {@link #equals} in terms of {@link #size} and {@link #containsAll}. If
82 * you override either of those methods, you may wish to override {@link #equals} to forward to
83 * this implementation.
84 *
85 * @since 7.0
86 */
87 protected boolean standardEquals(@Nullable Object object) {
88 return Sets.equalsImpl(this, object);
89 }
90
91 /**
92 * A sensible definition of {@link #hashCode} in terms of {@link #iterator}. If you override
93 * {@link #iterator}, you may wish to override {@link #equals} to forward to this implementation.
94 *
95 * @since 7.0
96 */
97 protected int standardHashCode() {
98 return Sets.hashCodeImpl(this);
99 }
100 }