@GwtCompatible public abstract class ForwardingObject extends Object
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<? extends T>)
. 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.
Modifier | Constructor and Description |
---|---|
protected |
ForwardingObject()
Constructor for use by subclasses.
|
protected ForwardingObject()
protected abstract Object delegate()
ForwardingSet.delegate()
. Concrete subclasses override this method to supply
the instance being decorated.Copyright © 2010-2015. All Rights Reserved.