Java Reference
In-Depth Information
public void
clear()
Clears this reference object so it has no referent object.
public boolean
enqueue()
Adds this reference object to the reference queue with which
it is registered, if any. Returns
TRue
if the reference object was
enqueued and
false
if there is no registered queue or this ref-
erence object was already enqueued.
public boolean
isEnqueued()
Returns
true
if this reference object has been enqueued
(either by the programmer or the garbage collector), and
false
otherwise.
We defer a discussion of reference queues until
Section 17.5.3
on page
459
.
Subclasses of
Reference
provide ways to bind the referent object to the
reference objectthe existing subclasses do this with a constructor argu-
ment. Once an object has been wrapped in a reference object you can
retrieve the object via
get
(and thus have a normal strong reference to
it) or you can clear the reference, perhaps making the referent unreach-
able. There is no means to change the object referred to by the referen-
ce object and you cannot subclass
Reference
directly.
17.5.2. Strengths of Reference and Reachability
In decreasing order of strength, the kinds of reference objects available
to you are
SoftReference<T>
,
WeakReference<T>
, and
PhantomReference<T>
.
These correspond to the reachability stages an object can pass through:
