Convert integer dates/times to unix timestamp in Java?

Question

This mainly applies to android, but could be used in Java. I have these listeners:

int year, month, day, hour, minute;
// the callback received when the user "sets" the date in the dialog
private DatePickerDialog.OnDateSetListener mDateSetListener =
        new DatePickerDialog.OnDateSetListener() {

            public void onDateSet(DatePicker view, int year, 
                                  int monthOfYear, int dayOfMonth) {
                year = year;
                month = monthOfYear;
                day = dayOfMonth;
            }
        };
// the callback received when the user "sets" the time in the dialog
private TimePickerDialog.OnTimeSetListener mTimeSetListener =
    new TimePickerDialog.OnTimeSetListener() {
        public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
            hour = hourOfDay;
            minute = minute;
        }
    };

How could I convert int year, month, day, hour, minute; to a unix timestamp? Is this possible without the Date class?

To avoid the Date object creation as stated here: http://stackoverflow.com/questions/732034/getting-unixtime-in-java — Mohit Deshpande, Jan 12 '11 at 21:29
Not possible without also having user's locale! (which I suppose you do in android, for but the general java extension, you don't have enough information in the sample to do it.) — Affe, Jan 12 '11 at 21:36

score 20 · Accepted Answer · edited Mar 04 '17 at 07:58

20

Okay, use Calendar then, since that's preferred to Date anyway:

int componentTimeToTimestamp(int year, int month, int day, int hour, int minute) {

    Calendar c = Calendar.getInstance();
    c.set(Calendar.YEAR, year);
    c.set(Calendar.MONTH, month);
    c.set(Calendar.DAY_OF_MONTH, day);
    c.set(Calendar.HOUR, hour);
    c.set(Calendar.MINUTE, minute);
    c.set(Calendar.SECOND, 0);
    c.set(Calendar.MILLISECOND, 0);

    return (int) (c.getTimeInMillis() / 1000L);
}

Calendar won't do any computations until getTimeMillis() is called and is designed to be more efficient than Date.

edited Mar 04 '17 at 07:58

CaptJak

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answered Jan 12 '11 at 21:42

Jerry Brady

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Would c.set(year, month, day, hour, minute, 0); work too? Since Calendar also has a method that takes a year, month, day of month, hour of day, minute, and second. – Mohit Deshpande Jan 13 '11 at 01:47
Not only would it work, it's more efficient, so yes setting them all with the same method call would be better still. – Jerry Brady Jan 17 '11 at 15:29
What about GregorianCalendar - would that be more efficient than Calendar? – IgorGanapolsky Jun 09 '14 at 22:01
@JerryBrady How is it more efficient? – OrhanC1 Sep 20 '15 at 13:51

Stephen P · Answer 2 · 2011-01-12T22:07:49.210

I'm assuming you want to avoid object overhead so I'm not suggesting any Date or Calendar classes; rather, you can calculate the value directly.

Unix time, or POSIX time, is a system for describing points in time, defined as the number of seconds elapsed since midnight Coordinated Universal Time (UTC) of January 1, 1970, not counting leap seconds. (Wikipedia article)

Calculate the number of days from Jan 1 1970 to the chosen year/month/day and multiply that by 24 * 3600, then add hour * 3600 + minute * 60 to get the number of seconds from 1970-01-01 00:00 to the chosen date and time.

There are well known algorithms for calculating the days between dates.

score 0 · Answer 3 · answered Jun 09 '13 at 13:41

Since I wanted to account for daylight saving as well, along with local timezone, so after searching for hours all the possible solutions, what worked for me was as follows:

int gmtOffset = TimeZone.getDefault().getRawOffset();
        int dstOffset = TimeZone.getDefault().getDSTSavings();
        long unix_timestamp = (System.currentTimeMillis() + gmtOffset + dstOffset) / 1000;

Convert integer dates/times to unix timestamp in Java?

3 Answers3