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/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;

import java.io.Serializable;

/**
 * An abstract base class for implementing the decorator pattern.
 * The {@link #delegate()} method must be overridden to return the instance
 * being decorated.
 *
 * 

This class does not forward the {@code hashCode} and {@code equals} * methods through to the backing object, but relies on {@code Object}'s * implementation. This is necessary to preserve the symmetry of {@code equals}. * Custom definitions of equality are usually based on an interface, such as * {@code Set} or {@code List}, so that the implementation of {@code equals} can * cast the object being tested for equality to the custom interface. {@code * ForwardingObject} implements no such custom interfaces directly; they * are implemented only in subclasses. Therefore, forwarding {@code equals} * would break symmetry, as the forwarding object might consider itself equal to * the object being tested, but the reverse could not be true. This behavior is * consistent with the JDK's collection wrappers, such as * {@link java.util.Collections#unmodifiableCollection}. Use an * interface-specific subclass of {@code ForwardingObject}, such as {@link * ForwardingList}, to preserve equality behavior, or override {@code equals} * directly. * *

The {@code toString} method is forwarded to the delegate. Although this * class does not implement {@link Serializable}, a serializable subclass may be * created since this class has a parameter-less constructor. * * @author Mike Bostock * @since 2.0 (imported from Google Collections Library) */ @GwtCompatible public abstract class ForwardingObject { /** Constructor for use by subclasses. */ protected ForwardingObject() {} /** * Returns the backing delegate instance that methods are forwarded to. * Abstract subclasses generally override this method with an abstract method * that has a more specific return type, such as {@link * ForwardingSet#delegate}. Concrete subclasses override this method to supply * the instance being decorated. */ protected abstract Object delegate(); /** * Returns the string representation generated by the delegate's * {@code toString} method. */ @Override public String toString() { return delegate().toString(); } /* No equals or hashCode. See class comments for details. */ }





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