RFR: 8336741: Optimize LocalTime.toString with StringBuilder.repeat

[Shaojin Wen]

On Thu, 18 Jul 2024 11:32:47 GMT, Shaojin Wen <duke at openjdk.org> wrote:

> class LocalTime {
>     public String toString() {
>         // ...
>                 if (nanoValue % 1000_000 == 0) {
>                     buf.append(Integer.toString((nanoValue / 1000_000) + 1000).substring(1));
>                 } else if (nanoValue % 1000 == 0) {
>                     buf.append(Integer.toString((nanoValue / 1000) + 1000_000).substring(1));
>                 } else {
>                     buf.append(Integer.toString((nanoValue) + 1000_000_000).substring(1));
>                 }
>        // ...
>     }
> }
> 
> Currently, LocalTime.toString handles nanos by adding a value and then subString(1) to fill it with zeros. Using StringBuilder.repeat is more concise and has better performance.

printFixedWidth cannot meet the needs of append nanos, For example, if the value is 1000, the output is `.000001`, not `.000001000`

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PR Comment: https://git.openjdk.org/jdk/pull/20232#issuecomment-2236588022