Class ForwardingObject

  extended by
Direct Known Subclasses:
ForwardingCache, ForwardingCollection, ForwardingExecutorService, ForwardingFuture, ForwardingIterator, ForwardingMap, ForwardingMapEntry, ForwardingMultimap, ForwardingService, ForwardingTable

public abstract class ForwardingObject
extends Object

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 Collections.unmodifiableCollection(java.util.Collection). Use an interface-specific subclass of ForwardingObject, such as ForwardingList, to preserve equality behavior, or override equals directly.

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

2.0 (imported from Google Collections Library)
Mike Bostock

Constructor Summary
protected ForwardingObject()
          Constructor for use by subclasses.
Method Summary
protected abstract  Object delegate()
          Returns the backing delegate instance that methods are forwarded to.
 String toString()
          Returns the string representation generated by the delegate's toString method.
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail


protected ForwardingObject()
Constructor for use by subclasses.

Method Detail


protected abstract Object delegate()
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.


public String toString()
Returns the string representation generated by the delegate's toString method.

toString in class Object

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