A DESCRIPTION OF THE PROBLEM :
Garbage is being generated when you call method StringBuilder.append(double).
I found that issue when I migrated from Java 17 to 21. We use LOGJ2 with garbage free configuration and now when you append double value append method generates garbage. It;s a problem because I see gc pauses every 1 second.

REGRESSION : Last worked in version 17.0.9

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
create any test when you call many times StringBuilder.append(dobule)

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
no gc
ACTUAL -
generate garbage

---------- BEGIN SOURCE ----------
@State(Scope.Benchmark)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Measurement(iterations = 5, time = 1)
@Warmup(iterations = 5, time = 1)
@Fork(1)
public class StringBuilderDoublePerf {
    private final StringBuilder b = new StringBuilder(128);

    @Benchmark
    @Threads(value = 1)
    public StringBuilder appendDouble() {
        b.setLength(0);
        return b.append(123.d);
    }

    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder()
                .include(StringBuilderDoublePerf.class.getSimpleName())
                .jvmArgs("-server",
                        "-XX:+UseG1GC",
                        "-Xmx2G",
                        "-XX:+AlwaysPreTouch"
                )
                // warmup
                .addProfiler(GCProfiler.class)
                .build();

        new Runner(opt).run();

    }
}
---------- END SOURCE ----------

FREQUENCY : always