[PATCH] Trivial improvement for j.l.Character.toString()

[Claes Redestad]

Looks good and trivial, including the drive-by cleanups.

I can sponsor.

/Claes

On 2020-03-25 22:18, Сергей Цыпанов wrote:
> Hello,
> 
> I think we can reduce allocation rate for j.l.Character.toString() by calling String.valueOf(char) instead of String.valueOf(char[]).
> 
> Current implementation creates char[] with one char which is later decoded into byte[].
> 
> Instead String.valueOf(char) decodes char directly consuming less memory. I've used benchmark [1]
> and on my machine got those results (JDK 14):
> 
> Benchmark                                                       Mode    Score     Error   Units
> 
> CharacterToStringBenchmark.toString_utf8                        avgt   14.723 ±   1.354   ns/op
> CharacterToStringBenchmark.valueOf_utf8                         avgt    7.678 ±   0.601   ns/op
> 
> CharacterToStringBenchmark.toString_latin                       avgt   10.992 ±   1.371   ns/op
> CharacterToStringBenchmark.valueOf_latin                        avgt    7.844 ±   1.044   ns/op
> 
> CharacterToStringBenchmark.toString_utf8:·gc.alloc.rate.norm    avgt   96.003 ±   0.001    B/op
> CharacterToStringBenchmark.valueOf_utf8:·gc.alloc.rate.norm     avgt   48.002 ±   0.001    B/op
> 
> CharacterToStringBenchmark.toString_latin:·gc.alloc.rate.norm   avgt   72.003 ±   0.001    B/op
> CharacterToStringBenchmark.valueOf_latin:·gc.alloc.rate.norm    avgt   48.002 ±   0.001    B/op
> 
> 
> Patch is below.
> 
> With best regards,
> Sergey Tsypanov
> 
> [1] https://github.com/stsypanov/strings/blob/master/src/jmh/java/tsypanov/strings/character/CharacterToStringBenchmark.java
> 
> diff --git a/src/java.base/share/classes/java/lang/Character.java b/src/java.base/share/classes/java/lang/Character.java
> --- a/src/java.base/share/classes/java/lang/Character.java
> +++ b/src/java.base/share/classes/java/lang/Character.java
> @@ -3285,7 +3285,7 @@
>                                "SYMBOLS AND PICTOGRAPHS EXTENDED-A",
>                                "SYMBOLSANDPICTOGRAPHSEXTENDED-A");
>   
> -        private static final int blockStarts[] = {
> +        private static final int[] blockStarts = {
>               0x0000,   // 0000..007F; Basic Latin
>               0x0080,   // 0080..00FF; Latin-1 Supplement
>               0x0100,   // 0100..017F; Latin Extended-A
> @@ -8068,7 +8068,7 @@
>               UNKNOWN,                  // E01F0..10FFFF
>           };
>   
> -        private static HashMap<String, Character.UnicodeScript> aliases;
> +        private static final HashMap<String, Character.UnicodeScript> aliases;
>           static {
>               aliases = new HashMap<>((int)(153 / 0.75f + 1.0f));
>               aliases.put("ADLM", ADLAM);
> @@ -8421,8 +8421,7 @@
>        * @return  a string representation of this object.
>        */
>       public String toString() {
> -        char buf[] = {value};
> -        return String.valueOf(buf);
> +        return toString(value);
>       }
>   
>       /**
>