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
050@ElementTypesAreNonnullByDefault
051public abstract class ForwardingSet<E extends @Nullable Object> extends ForwardingCollection<E>
052    implements Set<E> {
053  // TODO(lowasser): identify places where thread safety is actually lost
054
055  /** Constructor for use by subclasses. */
056  protected ForwardingSet() {}
057
058  @Override
059  protected abstract Set<E> delegate();
060
061  @Override
062  public boolean equals(@CheckForNull Object object) {
063    return object == this || delegate().equals(object);
064  }
065
066  @Override
067  public int hashCode() {
068    return delegate().hashCode();
069  }
070
071  /**
072   * A sensible definition of {@link #removeAll} in terms of {@link #iterator} and {@link #remove}.
073   * If you override {@code iterator} or {@code remove}, you may wish to override {@link #removeAll}
074   * to forward to this implementation.
075   *
076   * @since 7.0 (this version overrides the {@code ForwardingCollection} version as of 12.0)
077   */
078  @Override
079  protected boolean standardRemoveAll(Collection<?> collection) {
080    return Sets.removeAllImpl(this, checkNotNull(collection)); // for GWT
081  }
082
083  /**
084   * A sensible definition of {@link #equals} in terms of {@link #size} and {@link #containsAll}. If
085   * you override either of those methods, you may wish to override {@link #equals} to forward to
086   * this implementation.
087   *
088   * @since 7.0
089   */
090  protected boolean standardEquals(@CheckForNull Object object) {
091    return Sets.equalsImpl(this, object);
092  }
093
094  /**
095   * A sensible definition of {@link #hashCode} in terms of {@link #iterator}. If you override
096   * {@link #iterator}, you may wish to override {@link #equals} to forward to this implementation.
097   *
098   * @since 7.0
099   */
100  protected int standardHashCode() {
101    return Sets.hashCodeImpl(this);
102  }
103}