    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 static com.google.common.base.Preconditions.checkNotNull;
    020
    021    import com.google.common.annotations.Beta;
    022    import com.google.common.annotations.GwtCompatible;
    023
    024    import java.util.Collection;
    025    import java.util.Set;
    026
    027    import javax.annotation.Nullable;
    028
    029    /**
    030     * A set which forwards all its method calls to another set. Subclasses should
    031     * override one or more methods to modify the behavior of the backing set as
    032     * desired per the <a
    033     * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
    034     *
    035     * <p><b>Warning:</b> The methods of {@code ForwardingSet} forward
    036     * <b>indiscriminately</b> to the methods of the delegate. For example,
    037     * overriding {@link #add} alone <b>will not</b> change the behavior of {@link
    038     * #addAll}, which can lead to unexpected behavior. In this case, you should
    039     * override {@code addAll} as well, either providing your own implementation, or
    040     * delegating to the provided {@code standardAddAll} method.
    041     *
    042     * <p>The {@code standard} methods are not guaranteed to be thread-safe, even
    043     * when all of the methods that they depend on are thread-safe.
    044     *
    045     * @author Kevin Bourrillion
    046     * @author Louis Wasserman
    047     * @since 2.0 (imported from Google Collections Library)
    048     */
    049    @GwtCompatible
    050    public abstract class ForwardingSet<E> extends ForwardingCollection<E>
    051        implements Set<E> {
    052      // TODO(user): identify places where thread safety is actually lost
    053
    054      /** Constructor for use by subclasses. */
    055      protected ForwardingSet() {}
    056
    057      @Override protected abstract Set<E> delegate();
    058
    059      @Override public boolean equals(@Nullable Object object) {
    060        return object == this || delegate().equals(object);
    061      }
    062
    063      @Override public int hashCode() {
    064        return delegate().hashCode();
    065      }
    066
    067      /**
    068       * A sensible definition of {@link #removeAll} in terms of {@link #iterator}
    069       * and {@link #remove}.  If you override {@code iterator} or {@code remove},
    070       * you may wish to override {@link #removeAll} to forward to this
    071       * 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
    082       * {@link #containsAll}. If you override either of those methods, you may wish
    083       * to override {@link #equals} to forward to this implementation.
    084       *
    085       * @since 7.0
    086       */
    087      @Beta 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}.
    093       * If you override {@link #iterator}, you may wish to override {@link #equals}
    094       * to forward to this implementation.
    095       *
    096       * @since 7.0
    097       */
    098      @Beta protected int standardHashCode() {
    099        return Sets.hashCodeImpl(this);
    100      }
    101    }