[PATCH] Use StringJoiner where appropriate in java.base

[Kasper Nielsen]

Hi,

On Wed, 19 Jun 2019 at 14:12, Сергей Цыпанов <sergei.tsypanov at yandex.ru> wrote:
>
> Hello,
>
> in JDK code base we have many places (mainly in j.u.Arrays) where we convert array to String using verbose constructions with StringBuilder.
>
> As far as we have got StringJoiner for a long time we can use it making the code more simple.

It may make the code simpler, but it also comes with a hefty
performance penalty, taking twice as long in most cases compared to
the existing code.

A quick benchmark toString'ing int arrays of size 1,10,100,1000

Benchmark                    (size)  Mode  Cnt      Score     Error  Units
ToString2.toStringExisting        1  avgt    5     16.675 ±   0.327  ns/op
ToString2.toStringExisting       10  avgt    5     78.467 ±   1.373  ns/op
ToString2.toStringExisting      100  avgt    5    801.956 ±   7.517  ns/op
ToString2.toStringExisting     1000  avgt    5  14944.235 ± 155.393  ns/op

ToString2.toStringSuggested       1  avgt    5     35.053 ±   0.533  ns/op
ToString2.toStringSuggested      10  avgt    5    222.043 ±  10.157  ns/op
ToString2.toStringSuggested     100  avgt    5   2150.948 ±  13.285  ns/op
ToString2.toStringSuggested    1000  avgt    5  23411.264 ± 201.721  ns/op

/Kasper