class LocalTime {
    public String toString() {
        // ...
                if (nanoValue % 1000_000 == 0) {
                    buf.append(Integer.toString((nanoValue / 1000_000) + 1000).substring(1));
                } else if (nanoValue % 1000 == 0) {
                    buf.append(Integer.toString((nanoValue / 1000) + 1000_000).substring(1));
                } else {
                    buf.append(Integer.toString((nanoValue) + 1000_000_000).substring(1));
                }
       // ...
    }
}
Currently, LocalTime.toString handles nanos by adding a value and then subString(1) to fill it with zeros. Using StringBuilder.repeat is more concise and has better performance.