What is the difference between 'kk:mm', 'HH:mm', and 'hh:mm' in SimpleDateFormat?

Hour Format Specifiers in SimpleDateFormat

When employing SimpleDateFormat to format time values, it's crucial to understand the differences among the hour format specifiers kk:mm, HH:mm, and hh:mm.

kk:mm

The kk specifier represents hours on a 24-hour scale, ranging from 01 to 24. For instance, 24:00:00 indicates midnight.

HH:mm

Unlike kk, HH specifies hours on a 24-hour scale from 00 to 23. 00:00:00 denotes midnight.

hh:mm

The hh specifier displays hours on a 12-hour scale, using 01 to 12 in conjunction with AM/PM. Therefore, 12:00:00 AM or 12:00:00 PM would represent midday.

Consider the following Java code:

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));

This code prints the following output:

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

The discrepancy in working2's output is because the code sets working2's timezone but not its format. As a result, it wrongly displays 05:30:00 AM or PM, whereas it should output 12:00:00 AM.

The above is the detailed content of What is the difference between 'kk:mm', 'HH:mm', and 'hh:mm' in SimpleDateFormat?. For more information, please follow other related articles on the PHP Chinese website!