RFR: 8354724: BufferedReader readAllLines and readString methods [v5]

[Chen Liang]

On Fri, 18 Apr 2025 02:32:39 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> src/java.base/share/classes/java/io/Reader.java line 424:
>> 
>>> 422:         int n;
>>> 423:         while ((n = read(str)) != -1) {
>>> 424:             result.append(str, 0, n);
>> 
>> If the characters in the Reader are always Latin1, this process will convert the UTF16 char[] to the LATIN1 encoded byte[] value in the StringBuilder every time, which will cause unnecessary performance overhead.
>
> We need to provide a StringBuilder that creates a coder of UTF16 to avoid the unnecessary UTF16 to LATIN1 conversion overhead here. 
> 
> If we do not want to add a new public method, we can add an internal method and expose it through JLA for use here.

`Reader` by specification works on `char`, so I think this is fine. Even if a StringBuilder is UTF16, it still has to check for all-Latin1 characters at the time of string creation, so not really an overhead elimination.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24728#discussion_r2049929906