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 * Copyright (C) 2007 Google Inc.
 * 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
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.



 * An abstract base class for implementing the <a
 * href="">decorator pattern</a>.
 * The {@link #delegate()} method must be overridden to return the instance
 * being decorated.
 * This class does <i>not</i> 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.
 * <p>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
public abstract class ForwardingObject {

  /** Sole constructor. */
  protected ForwardingObject() {}
   * Returns the backing delegate instance that methods are forwarded to.
   * Abstract subclasses generally override the {@link ForwardingObject} 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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