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public class Test {
    public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String dateStr = "2023-12-31 23:59:59";
        try {
            Date date = sdf.parse(dateStr);

            String yearLowCase = sdf.format(date);
            System.out.println("LowYearCase: " + yearLowCase);

            SimpleDateFormat sdf2 = new SimpleDateFormat("YYYY-MM-dd HH:mm:ss");
            String yearUpperCase = sdf2.format(date);
            System.out.println("UpperYearCase: " + yearUpperCase);
        } catch (ParseException e) {
            throw new RuntimeException(e);
        }
    }
}