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    }