ConcurrentHashMap/ConcurrentMap/Map.compute

[Brian Goetz]

As a user, I have found the computeIfAbsent semantics more useful.

On 12/14/2012 11:08 AM, Doug Lea wrote:
> On 12/14/12 10:47, David M. Lloyd wrote:
>
>> Oh I see - the point I was missing is that computeIfAbsent is
>> specified to
>> return the *new* value if the mapping is replaced, instead of
>> returning null as
>> putIfAbsent does.
>>
>> Now given the precedent of putIfAbsent, why change the behavior in
>> this case?
>> Is it just because we are arguing that it was in fact a mistake?
>>
>
> For computeIfAbsent, the method must return the computed value
> to you or else you won't know it. The tradeoff is that the method
> cannot tell you whether you've computed it vs it was already there.
> The putIfAbsent method does provide this old vs new information,
> so is in principle more powerful in this restricted sense.
> But it is also susceptible to mistakes when people use
> the return value directly rather than checking if null.
>
> -Doug
>
>
>