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 CoSoCo.de> wrote: > 4.) Now we see, that javac optimization fails again if StringBuilder, concatenation, toString(), append(String), append(Collection) etc. and StringJoiner use is mixed.