Replace concat String to append in StringBuilder parameters

Wang Weijun at
Fri Aug 29 08:01:30 UTC 2014

So it's not that the optimization fails but there is no optimization on them yet.

I do see the .append("x") case will be easy to deal with, but it looks like historically javac has not been a place to do many optimizations. It mostly converts the java source to byte codes in a 1-to-1 mapping and let VM do whatever it wants (to optimize). When you talked about compiling multiple concatenation into using a single StringBuilder, it's more like choosing the correct implementation rather than an optimization.

I don't expect to see big change on this in the near future, so shall we go on with the current enhancement?


On Aug 29, 2014, at 2:17, Ulf Zibis <Ulf.Zibis at> wrote:

> I mean:
> It does not output byte code that only uses a single char array to compose the entire String in question.
> With "optimization fails", I also mean, there is used an additional "StringComposer" e.g. another StringBuilder or a StringJoiner in addition to the 1st StringBuilder.
> -Ulf
> Am 27.08.2014 um 14:02 schrieb Pavel Rappo:
>> Could you please explain what you mean by "javac optimization fails" here?
>> -Pavel
>> On 27 Aug 2014, at 10:41, Ulf Zibis <Ulf.Zibis at> wrote:
>>> 4.) Now we see, that javac optimization fails again if StringBuilder, concatenation, toString(), append(String), append(Collection) etc. and StringJoiner use is mixed.

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