Several attempts have been made to improve Formatter's numeric performance by caching the current Locale zero. Such fixes, however, ignore the real issue, which is the slowness of fetching DecimalFormatSymbols. By directly caching DecimalFormatSymbols in the Formatter, this enhancement streamlines the process of accessing Locale DecimalFormatSymbols and specifically getZeroDigit(). The result is a general improvement in the performance of numeric formatting.

@Benchmark
public void bigDecimalDefaultLocale() {
    result = String.format("%1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f", X);
}

@Benchmark
public void bigDecimalLocaleAlternate() {
    result = String.format(THAI, "%1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f", X);
    other = String.format(DEFAULT, "%1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f", X);
}

@Benchmark
public void bigDecimalThaiLocale() {
    result = String.format(THAI, "%1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f", X);
}

@Benchmark
public void integerDefaultLocale() {
    result = String.format("%1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d", x);
}

@Benchmark
public void integerLocaleAlternate() {
    result = String.format(THAI, "%1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d", x);
    other = String.format(DEFAULT, "%1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d", x);
}

@Benchmark
public void integerThaiLocale() {
    result = String.format(THAI, "%1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d", x);
}


Before:
Benchmark Mode Cnt Score Error Units
MyBenchmark.bigDecimalDefaultLocale thrpt 25 75498.923 ± 3686.966 ops/s
MyBenchmark.bigDecimalLocaleAlternate thrpt 25 39068.721 ± 162.983 ops/s
MyBenchmark.bigDecimalThaiLocale thrpt 25 77256.530 ± 294.743 ops/s
MyBenchmark.integerDefaultLocale thrpt 25 344093.071 ± 6189.002 ops/s
MyBenchmark.integerLocaleAlternate thrpt 25 165685.488 ± 440.857 ops/s
MyBenchmark.integerThaiLocale thrpt 25 327461.302 ± 1168.243 ops/s

After:
Benchmark Mode Cnt Score Error Units
MyBenchmark.bigDecimalDefaultLocale thrpt 25 94735.293 ± 674.587 ops/s
MyBenchmark.bigDecimalLocaleAlternate thrpt 25 44215.547 ± 291.664 ops/s
MyBenchmark.bigDecimalThaiLocale thrpt 25 91390.997 ± 658.677 ops/s
MyBenchmark.integerDefaultLocale thrpt 25 363722.977 ± 2864.554 ops/s
MyBenchmark.integerLocaleAlternate thrpt 25 165789.514 ± 779.656 ops/s
MyBenchmark.integerThaiLocale thrpt 25 351400.818 ± 1030.246 ops/s