CODEWITHSUNDEEP
java
ark1974
ark1974

Reputation: 655

Calculating time difference in hours

I am a newbie in java. I have written this function to find the time difference in hours from the current time to the time in function parameters. The results are kind of mixed, how I can I improve it? Thanks.

private int getTimeDiffFromCurrent(String date, String time)
    {
        String str_date_time = date + " " + time;
        DateFormat formatter = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss", Locale.getDefault());

        try {
            Date date_time = (Date) formatter.parse(str_date_time); 
            int hr = (int)((System.currentTimeMillis() - date_time.getTime())/(1000 * 60 * 60));
            return hr>=0? hr : 1000;
        }
        catch (Exception e) {
            System.out.println(e.toString() + ", " + str_date_time);
        }    
        return 1000;
    }

Example of used case:

getTimeDiffFromCurrent("19/07/2020", "07:19:00");

Upvotes: 0

Views: 115

Answers (1)

MC Emperor
MC Emperor

Reputation: 22977

If you use the Java Date and Time API available in the java.time package, then it'll becomes much simpler.

static long getDifferenceInHours(ZonedDateTime dateTime) {
    ZonedDateTime now = ZonedDateTime.now();
    return Duration
        .between(dateTime, now)
        .toHours();
}

You can then call it like this:

ZonedDateTime zdt = ZonedDateTime.of(2020, 7, 16, 0, 0, 0, 0, ZoneId.systemDefault());
long difference = getDifferenceInHours(zdt);
System.out.println(difference);

You shouldn't apply math to calculate date and time differences; there are many APIs out there doing the job pretty well.

I used ZonedDateTime in the abovementioned code, because this takes possible DST changes into consideration. For example, in the Europe/Amsterdam timezone, between 29th March 2020, 00:00 and 05:00 are just 4 hours (instead of 5) due to the wall clock skipping an hour at two.

Upvotes: 3

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