I did miss the point (or in fact the little word "not").
I think your theory is probably right, although in the absence of
arbitrary operator overloading it seems quite clear what the type of
(getOne() + "two ") is and since string concatenation is associative it
would be a valid optimization. But it requires a bit more reasoning.
Even with operator overloading the case would IMO still be clear since
the return type of getOne() is exact due to String's finalness. But
then: we are talking Java, other JVM languages might break some of these
rules.
Peter
Christian Catchpole wrote:
> hmm.. think you missed the point there peter. "two " + "three" ==
> "two three" regardless of what comes before it. But I think i might
> know why the optimizer picks up
>
> "one " + "two " + "three"
>
> but not
>
> getOne() + "two " + "three"
>
> it probably sees this..
>
> (("one " + "two ") + "three")
> ==
> (("one two ") + "three")
> ==
> ("one two three")
>
> It can collapse one two, then the third because they are all constant.
>
> ((getOne() + "two ") + "three")
>
> the first collapse produces something unpredictable.
>
> On Aug 27, 7:43 am, Peter Becker <peter.becker...@gmail.com> wrote:
>
>> Alexey Zinger wrote:
>>
>>> There are quite a few optimizations with strings, for sure. Such as
>>> replacing concatenation using "+" operator with StringBuilder and
>>> concatenation of literals with a single literal (*).
>>>
>>> There's an interesting exception to that rule. The following will
>>> work as expected:
>>> "one " + "two " + "three"
>>> gets turned into
>>> "one two three"
>>>
>>> However, in the context of this: public String getOne() { return "one "; }
>>> this: getOne() + "two " + "three"
>>> will not get turned into
>>> getOne() + "two three"
>>>
>> If I am not mistaken the compiler can not replace that without
>> potentially breaking the code. You method is public and non-final, which
>> means it can be overwritten, so you need the dynamic dispatch, inlining
>> is not ok.
>>
>> The JIT might do a different thing since it knows the state of the
>> running system. If it should optimize that call it will need to be able
>> to revert it if a baseclass of the class you describe is loaded.
>>
>> If the method getOne() would be either final or private, then the
>> compiler should theoretically be able to inline it. No idea if it would.
>>
>> Peter
>>
> >
>
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