    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
    017    package com.google.common.collect;
    018
    019    import com.google.common.annotations.Beta;
    020    import com.google.common.annotations.GwtCompatible;
    021
    022    import java.util.Set;
    023
    024    import javax.annotation.Nullable;
    025
    026    /**
    027     * A set which forwards all its method calls to another set. Subclasses should
    028     * override one or more methods to modify the behavior of the backing set as
    029     * 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
    033     * <b>indiscriminately</b> to the methods of the delegate. For example,
    034     * overriding {@link #add} alone <b>will not</b> change the behavior of {@link
    035     * #addAll}, which can lead to unexpected behavior. In this case, you should
    036     * override {@code addAll} as well, either providing your own implementation, or
    037     * delegating to the provided {@code standardAddAll} method.
    038     *
    039     * <p>The {@code standard} methods are not guaranteed to be thread-safe, even
    040     * when all of the methods that they depend on are thread-safe.
    041     *
    042     * @author Kevin Bourrillion
    043     * @author Louis Wasserman
    044     * @since 2.0 (imported from Google Collections Library)
    045     */
    046    @GwtCompatible
    047    public abstract class ForwardingSet<E> extends ForwardingCollection<E>
    048        implements Set<E> {
    049      // TODO(user): identify places where thread safety is actually lost
    050
    051      /** Constructor for use by subclasses. */
    052      protected ForwardingSet() {}
    053
    054      @Override protected abstract Set<E> delegate();
    055
    056      @Override public boolean equals(@Nullable Object object) {
    057        return object == this || delegate().equals(object);
    058      }
    059
    060      @Override public int hashCode() {
    061        return delegate().hashCode();
    062      }
    063
    064      /**
    065       * A sensible definition of {@link #equals} in terms of {@link #size} and
    066       * {@link #containsAll}. If you override either of those methods, you may wish
    067       * to override {@link #equals} to forward to this implementation.
    068       *
    069       * @since 7.0
    070       */
    071      @Beta protected boolean standardEquals(@Nullable Object object) {
    072        return Sets.equalsImpl(this, object);
    073      }
    074
    075      /**
    076       * A sensible definition of {@link #hashCode} in terms of {@link #iterator}.
    077       * If you override {@link #iterator}, you may wish to override {@link #equals}
    078       * to forward to this implementation.
    079       *
    080       * @since 7.0
    081       */
    082      @Beta protected int standardHashCode() {
    083        return Sets.hashCodeImpl(this);
    084      }
    085    }