RFR: 8341566: Adding factory for non-synchronized CharSequence Reader

[Markus KARG]

On Sun, 6 Oct 2024 14:21:30 GMT, Chen Liang <liach 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.
>
> src/java.base/share/classes/java/io/Reader.java line 163:
> 
>> 161:      * {@code transferTo()} methods all throw {@code IOException}.
>> 162:      *
>> 163:      * <p> The {@code markSupported()} method returns {@code true}.
> 
> Suggestion:
> 
>      * <p>The returned reader supports the {@link #mark mark()} operation.

This is not wrong. This style is used all over the place already within `Reader.java`, so it would be strange to change it *just here*.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21371#discussion_r1789121226