Hi Mandy,
On 07/10/2018 12:18 AM, mandy chung wrote:
On 7/9/18 12:59 PM, Per Liden wrote:
On 2018-07-09 20:49, mandy chung wrote:
On 7/9/18 11:31 AM, Zheka Kozlov wrote:
It is possible to create a
WeakReference/SoftReference/PhantomReference
with a null value in which case the Reference will never be
enqueued. This
is quite obvious (since null cannot be weakly/softly/phantom
reachable).
But I think it's worth being mentioned in the JavaDoc. What do you
think?
Alternatively, the constructor should require non-null referent and
throws NPE if null.
I created https://bugs.openjdk.java.net/browse/JDK-8206933 to track
this.
It's not completely obvious to me that throwing NPE or otherwise
blocking this is the right thing to do. Sure, creating a Reference
with a null referent seems pretty useless, but it's also very similar
to creating a Reference and immediately calling its clear() method,
which is perfectly valid (and equally useless).
Are you saying we should block this because we can easily detect this
particular case/misuse, as opposed to the immediately-called-clear
case? Or is there some other rationale?
I don't expect any one wants to create a reference with null referent
Throwing NPE would be one way to catch if a reference object is created
with null referent. I think the compatibility risk is low.
I agree that Reference::clear is equally useless. Are you thinking
something should be done with Reference::clear?
Mandy
There are situations where being able to create a XxxReference without a
referent is useful. For example, imagine a doubly-linked list of
WeakReference subclasses - a special instance without a referent can be
used as the head of such list that never goes away and simplifies
insertion/deletion logic, etc...
JDK's java.lang.ref.Cleaner API uses such scheme in its implementation
(see jdk.internal.ref.CleanerImpl.[Phantom|Weak|Soft]CleanableRef no-arg
constructors).
Regards, Peter
