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    }