JAVA中日期 yyyy-MM-dd HH：mm：ss和yyyy-MM-dd hh：mm：ss的区别

//24小时制
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
//12小时制
SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");

String date1 = "2017-04-23 16:45:12";
try {
    sdf.parse(date1);
    System.out.println(sdf.format(sdf.parse(date1))); //2017-04-23 16:45:12
    System.out.println(sdf1.format(sdf.parse(date1))); //2017-04-23 04:45:12
} catch (ParseException e) {
    e.printStackTrace();
}