RFR: 8358533: Improve performance of java.io.Reader.readAllLines [v3]

[Brian Burkhalter]

On Mon, 23 Jun 2025 21:23:05 GMT, Stuart Marks <smarks at openjdk.org> wrote:

>> src/java.base/share/classes/java/io/Reader.java line 508:
>> 
>>> 506:         }
>>> 507: 
>>> 508:         return lines;
>> 
>> Do we really want to return a mutable `ArrayList` here? In earlier discussions about this very API I was told that it deliberately returns `String` instead of `CharSequence` due to *intended* immutability, even if that potentially implied slower performance. Following this logic, it would be just straightforward to `return Collections.unmodifiableList(lines);` here. 🤔
>
> Right, the specification here requires an unmodifiable List, so an unmodifiable wrapper or a list from `List.copyOf()` is appropriate.

Fixed in [d5abfa4](https://github.com/openjdk/jdk/pull/25863/commits/d5abfa450cb3fcd604560833038735e41952bce9
).

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/25863#discussion_r2164687743