RFR: 8341566: Adding factory for non-synchronized CharSequence Reader [v4]

[Jaikiran Pai]

On Tue, 8 Oct 2024 11:23:42 GMT, Markus KARG <duke at openjdk.org> wrote:

>> This Pull Requests proposes an implementation for [JDK-8341566](https://bugs.openjdk.org/browse/JDK-8341566): Adding the new method `public static Reader Reader.of(CharSequence)` will return an anonymous, non-synchronized implementation of a `Reader` for each kind of `CharSequence` implementation. It is optimized for `String`, `StringBuilder`, `StringBuffer` and `CharBuffer`.
>> 
>> In addition, this Pull Request proposes to replace the implementation of `StringReader` to become a simple synchronized wrapper around `Reader.of(CharSequence)` for the case of `String` sources. To ensure correctness, this PR...
>> * ...simply moved the **original code** of `StringBuilder` to become the de-facto implementation of `Reader.of()`, then stripped synchronized from it on the left hand, but kept just a synchronized wrapper on the right hand. Then added a `switch` for optimizations within the original code, at the exact location where previously just an optimization for `String` lived in.
>> * ...added tests for all methods (`Of.java`), and applied that test upon the modified `StringBuilder`.
>> 
>> Wherever new JavaDocs were added, existing phrases from other code locations have been copied and adapted, to best match the same wording.
>
> Markus KARG has updated the pull request incrementally with six additional commits since the last revision:
> 
>  - renamed source to cs; cs is final; close sets boolean; no adouble reference to source
>  - Fixed Typo: 'resect' -> 'respect'
>  - Improved wording: 'The returned reader supports the {@link #mark mark()} operation'
>  - Improved wording: 'Returns a {@code Reader} that reads characters from a {@code CharSequence}, starting at the first character in the sequence'
>  - test for generic read(char, int, int) case
>  - Remove useless test

src/java.base/share/classes/java/io/Reader.java line 174:

> 172: 
> 173:         return new Reader() {
> 174:             private final int length = cs.length();

Hello Markus, as far as I can see, a  `CharSequence` is allowed to have a non-fixed `length()` (typically allowed to increase?). Is there a reason why the length is captured at construction time instead of being evaluated during the read operations of the `Reader`?

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PR Review Comment: https://git.openjdk.org/jdk/pull/21371#discussion_r1791734338