AS of JDK 17 some of primitive wrappers, e.g. Long, Integer, Double and Float in their implementations of Object.toString() delegate to utility toString(primitive) methods.

Unlike those, Boolea, Byte, Character and Short just duplicate the contents of utility methods in implementations of Object.toString().

Yet another issue is a tiny discrepancy in implementation related to Byte and Short: (see e.g. Byte):

public static String toString(byte b) {
    return Integer.toString((int)b, 10);
}

public String toString() {
    return Integer.toString((int)value);
}

Unlike in overriden method, In utility one they explicitly specify radix which can be skipped, as implementation of Integer.toString(int,int) has a fast-path for radix 10, ending in Integer.toString(int). This simplification gives tiny improvement, see benchmark:

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g"})
public class ByteToStringBenchmark {
    @Benchmark
    public String byteToString() {
        return Byte.toString((byte) 1);
    }
}

Before

Benchmark Mode Cnt Score Error Units
ByteToStringBenchmark.byteToString avgt 30 11,648 ± 1,906 ns/op

After

Benchmark Mode Cnt Score Error Units
ByteToStringBenchmark.byteToString avgt 30 10,016 ± 0,530 ns/op