@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.
|
Modifier and Type | Method and Description |
---|---|
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. |
protected ForwardingObject()
protected abstract Object delegate()
ForwardingSet.delegate()
. Concrete subclasses override this method to supply the
instance being decorated.Copyright © 2010–2019. All rights reserved.