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 static com.google.common.base.Preconditions.checkNotNull;
020
021import com.google.common.annotations.GwtCompatible;
022import java.util.Collection;
023import java.util.Set;
024import org.checkerframework.checker.nullness.qual.Nullable;
025
026/**
027 * A set which forwards all its method calls to another set. Subclasses should override one or more
028 * methods to modify the behavior of the backing set as desired per the <a
029 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
030 *
031 * <p><b>Warning:</b> The methods of {@code ForwardingSet} forward <b>indiscriminately</b> to the
032 * methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change the
033 * behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should
034 * override {@code addAll} as well, either providing your own implementation, or delegating to the
035 * provided {@code standardAddAll} method.
036 *
037 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
038 * default} methods. Instead, it inherits their default implementations. When those implementations
039 * invoke methods, they invoke methods on the {@code ForwardingSet}.
040 *
041 * <p>The {@code standard} methods are not guaranteed to be thread-safe, even when all of the
042 * methods that they depend on are thread-safe.
043 *
044 * @author Kevin Bourrillion
045 * @author Louis Wasserman
046 * @since 2.0
047 */
048@GwtCompatible
049public abstract class ForwardingSet<E> extends ForwardingCollection<E> implements Set<E> {
050  // TODO(lowasser): identify places where thread safety is actually lost
051
052  /** Constructor for use by subclasses. */
053  protected ForwardingSet() {}
054
055  @Override
056  protected abstract Set<E> delegate();
057
058  @Override
059  public boolean equals(@Nullable Object object) {
060    return object == this || delegate().equals(object);
061  }
062
063  @Override
064  public int hashCode() {
065    return delegate().hashCode();
066  }
067
068  /**
069   * A sensible definition of {@link #removeAll} in terms of {@link #iterator} and {@link #remove}.
070   * If you override {@code iterator} or {@code remove}, you may wish to override {@link #removeAll}
071   * to forward to this implementation.
072   *
073   * @since 7.0 (this version overrides the {@code ForwardingCollection} version as of 12.0)
074   */
075  @Override
076  protected boolean standardRemoveAll(Collection<?> collection) {
077    return Sets.removeAllImpl(this, checkNotNull(collection)); // for GWT
078  }
079
080  /**
081   * A sensible definition of {@link #equals} in terms of {@link #size} and {@link #containsAll}. If
082   * you override either of those methods, you may wish to override {@link #equals} to forward to
083   * this implementation.
084   *
085   * @since 7.0
086   */
087  protected boolean standardEquals(@Nullable Object object) {
088    return Sets.equalsImpl(this, object);
089  }
090
091  /**
092   * A sensible definition of {@link #hashCode} in terms of {@link #iterator}. If you override
093   * {@link #iterator}, you may wish to override {@link #equals} to forward to this implementation.
094   *
095   * @since 7.0
096   */
097  protected int standardHashCode() {
098    return Sets.hashCodeImpl(this);
099  }
100}