How to get number of days between two calendar instance?

Question

I want to find the difference between two Calendar objects in number of days if there is date change like If clock ticked from 23:59-0:00 there should be a day

Answer 1

This function computes the number of days between two Calendars as the number of calendar days of the month that are between them, which is what the OP wanted. The calculation is performed by counting how many multiples of 86,400,000 milliseconds are between the calendars after both have been set to midnight of their respective days.

For example, my function will compute 1 day's difference between a Calendar on January 1, 11:59PM and January 2, 12:01AM.

import java.util.concurrent.TimeUnit;

/**
 * Compute the number of calendar days between two Calendar objects. 
 * The desired value is the number of days of the month between the
 * two Calendars, not the number of milliseconds' worth of days.
 * @param startCal The earlier calendar
 * @param endCal The later calendar
 * @return the number of calendar days of the month between startCal and endCal
 */
public static long calendarDaysBetween(Calendar startCal, Calendar endCal) {

    // Create copies so we don't update the original calendars.

    Calendar start = Calendar.getInstance();
    start.setTimeZone(startCal.getTimeZone());
    start.setTimeInMillis(startCal.getTimeInMillis());

    Calendar end = Calendar.getInstance();
    end.setTimeZone(endCal.getTimeZone());
    end.setTimeInMillis(endCal.getTimeInMillis());

    // Set the copies to be at midnight, but keep the day information.

    start.set(Calendar.HOUR_OF_DAY, 0);
    start.set(Calendar.MINUTE, 0);
    start.set(Calendar.SECOND, 0);
    start.set(Calendar.MILLISECOND, 0);

    end.set(Calendar.HOUR_OF_DAY, 0);
    end.set(Calendar.MINUTE, 0);
    end.set(Calendar.SECOND, 0);
    end.set(Calendar.MILLISECOND, 0);

    // At this point, each calendar is set to midnight on 
    // their respective days. Now use TimeUnit.MILLISECONDS to
    // compute the number of full days between the two of them.

    return TimeUnit.MILLISECONDS.toDays(
            Math.abs(end.getTimeInMillis() - start.getTimeInMillis()));
}