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

Сергей Цыпанов sergei.tsypanov at yandex.ru
Wed Mar 25 21:18:54 UTC 2020


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);
     }
 
     /**



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