[java] Difference between java HH:mm and hh:mm on SimpleDateFormat

Whats the difference between kk:mm, HH:mm and hh:mm formats ??

    SimpleDateFormat broken = new SimpleDateFormat("kk:mm:ss");
    broken.setTimeZone(TimeZone.getTimeZone("Etc/UTC"));
    SimpleDateFormat working = new SimpleDateFormat("HH:mm:ss");
    working.setTimeZone(TimeZone.getTimeZone("Etc/UTC"));
    SimpleDateFormat working2 = new SimpleDateFormat("hh:mm:ss");
    working.setTimeZone(TimeZone.getTimeZone("Etc/UTC"));

    System.out.println(broken.format(epoch));
    System.out.println(working.format(epoch));
    System.out.println(working2.format(epoch));

prints:

24:00:00
00:00:00
05:30:00

Actually the last one is not weird. Code is setting the timezone for working instead of working2.

SimpleDateFormat working2 = new SimpleDateFormat("hh:mm:ss"); working.setTimeZone(TimeZone.getTimeZone("Etc/UTC"));

kk goes from 1 to 24, HH from 0 to 23 and hh from 1 to 12 (AM/PM).

Fixing this error gives:

24:00:00
00:00:00
01:00:00

Use the built-in localized formats

If this is for showing a time of day to a user, then in at least 19 out of 20 you don’t need to care about kk, HH nor hh. I suggest that you use something like this:

    DateTimeFormatter defaultTimeFormatter
            = DateTimeFormatter.ofLocalizedTime(FormatStyle.SHORT);
    System.out.format("%s: %s%n",
            Locale.getDefault(), LocalTime.MIN.format(defaultTimeFormatter));

The point is that it gives different output in different default locales. For example:

en_SS: 12:00 AM
fr_BL: 00:00
ps_AF: 0:00
es_CO: 12:00 a.m.

The localized formats have been designed to conform with the expectations of different cultures. So they generally give the user a better experience and they save you of writing a format pattern string, which is always error-prone.

I furthermore suggest that you don’t use SimpleDateFormat. That class is notoriously troublesome and fortunately long outdated. Instead I use java.time, the modern Java date and time API. It is so much nicer to work with.

Four pattern letters for hour: H, h, k and K

Of course if you need to parse a string with a specified format, and also if you have a very specific formatting requirement, it’s good to use a format pattern string. There are actually four different pattern letters to choose from for hour (quoted from the documentation):

  Symbol  Meaning                     Presentation      Examples
  ------  -------                     ------------      -------
   h       clock-hour-of-am-pm (1-12)  number            12
   K       hour-of-am-pm (0-11)        number            0
   k       clock-hour-of-day (1-24)    number            24
   H       hour-of-day (0-23)          number            0

In practice H and h are used. As far as I know k and K are not (they may just have been included for the sake of completeness). But let’s just see them all in action:

    DateTimeFormatter timeFormatter
            = DateTimeFormatter.ofPattern("hh:mm a  HH:mm  kk:mm  KK:mm a", Locale.ENGLISH);
    System.out.println(LocalTime.of(0, 0).format(timeFormatter));
    System.out.println(LocalTime.of(1, 15).format(timeFormatter));
    System.out.println(LocalTime.of(11, 25).format(timeFormatter));
    System.out.println(LocalTime.of(12, 35).format(timeFormatter));
    System.out.println(LocalTime.of(13, 40).format(timeFormatter));

12:00 AM  00:00  24:00  00:00 AM
01:15 AM  01:15  01:15  01:15 AM
11:25 AM  11:25  11:25  11:25 AM
12:35 PM  12:35  12:35  00:35 PM
01:40 PM  13:40  13:40  01:40 PM

If you don’t want the leading zero, just specify one pattern letter, that is h instead of hh or H instead of HH. It will still accept two digits when parsing, and if a number to be printed is greater than 9, two digits will still be printed.

Links

• Oracle tutorial: Date Time explaining how to use java.time.
• Documentation of DateTimeFormatter .

kk: (01-24) will look like 01, 02..24.

HH:(00-23) will look like 00, 01..23.

hh:(01-12 in AM/PM) will look like 01, 02..12.

so the last printout (working2) is a bit weird. It should say 12:00:00 (edit: if you were setting the working2 timezone and format, which (as kdagli pointed out) you are not)

Please take a look here

HH is hour in a day (starting from 0 to 23)

hh are hours in am/pm format

kk is hour in day (starting from 1 to 24)

mm is minute in hour

ss are the seconds in a minute

h/H = 12/24 hours means you will write hh:mm = 12 hours format and HH:mm = 24 hours format