- Direct Known Subclasses:
@GwtCompatible public abstract class ForwardingObject extends ObjectAn 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
equalsmethods 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
List, so that the implementation of
equalscan cast the object being tested for equality to the custom interface.
ForwardingObjectimplements no such custom interfaces directly; they are implemented only in subclasses. Therefore, forwarding
equalswould 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<? extends T>). Use an interface-specific subclass of
ForwardingObject, such as
ForwardingList, to preserve equality behavior, or override
toStringmethod 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.
- Mike Bostock
Constructors Modifier Constructor Description
ForwardingObject()Constructor for use by subclasses.
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description
protected abstract Object
delegate()Returns the backing delegate instance that methods are forwarded to.
toString()Returns the string representation generated by the delegate's
protected ForwardingObject()Constructor for use by subclasses.
delegateReturns 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.