Calculate Date/Time Difference in Java considering AM/PM

Question

I want to calculate the difference between two date/time in java using Date and Calendar classes. The format that I have is \"2012-01-24 12:30:00 PM\".

I have implem

Answer 1

Don't build it yourself, use an established library. Jodatime is used widely.

Answer 2

Calendar has a methode add() that can be used for substracting too. Take a look at it. You should be using Calendar instead of Date anyway because most of the Date operations are deprecated.

Answer 3

The problem is your date format: instead of yyyy-MM-dd HH:mm:ss a use yyyy-MM-dd hh:mm:ss a.

HH will be the hour in day (0-23) whereas hh will be the hour in AM/PM (1-12). Thus with your date format 02:30:00 will be parsed as just that instead of being converted to the PM version (which in hour of day would be 14:30:00).

Answer 4

So, you have these dates as strings? Parse them with a SimpleDateFormat with the appropriate format string, and compute the difference in hours:

DateFormat df = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss a");

Date d1 = df.parse("2012-01-24 12:30:00 PM");
Date d2 = df.parse("2012-01-24 02:30:00 PM");

int hoursDifference = (int)((d2.getTime() - d1.getTime()) / 3600000L);
System.out.println("Difference in hours: " + hoursDifference);

Your error is that you are using HH (24-hour hours) instead of hh (12-hour hours) in your format string.

Answer 5

onsider using Apache Commons DateUtils DurationFormatUtils formatPeriod method will do the magic.

Good luck!

EDIT Assuming that you have Date a and Date b initialized at this point,

String format="HH:mm:ss.SSS";   // whatever you wish
boolean padWithZeros=true; // whatever you wish
TimeZone timezone=null; // whatever you wish
long timeA = a.getTime();
long timeB = b.getTime();

String period = DurationFormatUtils.formatPeriod(timeB, timeA, format, padWithZeros, timezone);

Answer 6

The reason why it shows 10 hours as the difference is that you've got an error in the pattern when parsing the input.

Here's an example using SimpleDateFormat:

SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss a");

Date date1 = df.parse("2012-01-24 12:30:00 PM");
Date date2 = df.parse("2012-01-24 02:30:00 PM");

long differenceInHours = Math.abs(date1.getTime() - date2.getTime()) / 1000 / 60 / 60);

Will return 10.

When we just slightly change the date format pattern, using hh for hour in am/pm (1-12) instead of HH for hour in day (0-23):

SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss a");

It returns (the expected) 2.

See the documentation for SimpleDateFormat to get your patterns right.