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 javax.annotation.CheckForNull;
025import org.checkerframework.checker.nullness.qual.Nullable;
026
027/**
028 * A set which forwards all its method calls to another set. Subclasses should override one or more
029 * methods to modify the behavior of the backing set as desired per the <a
030 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
031 *
032 * <p><b>Warning:</b> The methods of {@code ForwardingSet} forward <b>indiscriminately</b> to the
033 * methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change the
034 * behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should
035 * override {@code addAll} as well, either providing your own implementation, or delegating to the
036 * provided {@code standardAddAll} method.
037 *
038 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
039 * default} methods. Instead, it inherits their default implementations. When those implementations
040 * invoke methods, they invoke methods on the {@code ForwardingSet}.
041 *
042 * <p>The {@code standard} methods are not guaranteed to be thread-safe, even when all of the
043 * methods that they depend on are thread-safe.
044 *
045 * @author Kevin Bourrillion
046 * @author Louis Wasserman
047 * @since 2.0
048 */
049@GwtCompatible
050public abstract class ForwardingSet<E extends @Nullable Object> extends ForwardingCollection<E>
051    implements Set<E> {
052  // TODO(lowasser): identify places where thread safety is actually lost
053
054  /** Constructor for use by subclasses. */
055  protected ForwardingSet() {}
056
057  @Override
058  protected abstract Set<E> delegate();
059
060  @Override
061  public boolean equals(@CheckForNull Object object) {
062    return object == this || delegate().equals(object);
063  }
064
065  @Override
066  public int hashCode() {
067    return delegate().hashCode();
068  }
069
070  /**
071   * A sensible definition of {@link #removeAll} in terms of {@link #iterator} and {@link #remove}.
072   * If you override {@code iterator} or {@code remove}, you may wish to override {@link #removeAll}
073   * to forward to this implementation.
074   *
075   * @since 7.0 (this version overrides the {@code ForwardingCollection} version as of 12.0)
076   */
077  @Override
078  protected boolean standardRemoveAll(Collection<?> collection) {
079    return Sets.removeAllImpl(this, checkNotNull(collection)); // for GWT
080  }
081
082  /**
083   * A sensible definition of {@link #equals} in terms of {@link #size} and {@link #containsAll}. If
084   * you override either of those methods, you may wish to override {@link #equals} to forward to
085   * this implementation.
086   *
087   * @since 7.0
088   */
089  protected boolean standardEquals(@CheckForNull Object object) {
090    return Sets.equalsImpl(this, object);
091  }
092
093  /**
094   * A sensible definition of {@link #hashCode} in terms of {@link #iterator}. If you override
095   * {@link #iterator}, you may wish to override {@link #equals} to forward to this implementation.
096   *
097   * @since 7.0
098   */
099  protected int standardHashCode() {
100    return Sets.hashCodeImpl(this);
101  }
102}