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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
 * 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 decorator pattern. The delegate() method must be overridden to return the instance being decorated.

This class does not forward the hashCode and equals methods through to the backing object, but relies on Object's implementation. This is necessary to preserve the symmetry of equals. Custom definitions of equality are usually based on an interface, such as Set or List, so that the implementation of equals can cast the object being tested for equality to the custom interface. ForwardingObject implements no such custom interfaces directly; they are implemented only in subclasses. Therefore, forwarding 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 java.util.Collections.unmodifiableCollection(java.util.Collection). Use an interface-specific subclass of ForwardingObject, such as, to preserve equality behavior, or override equals directly.

The toString method is forwarded to the delegate. Although this class does not implement, a serializable subclass may be created since this class has a parameter-less constructor.

Mike Bostock
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 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 toString method.
  public String toString() {
    return delegate().toString();
  /* No equals or hashCode. See class comments for details. */
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