WeakReference with null referent

mandy chung mandy.chung at oracle.com
Mon Jul 9 22:18:10 UTC 2018

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?


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