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

Here's my solution using good old Calendar objects:

public static int daysApart(Calendar d0,Calendar d1)
{
    int days=d0.get(Calendar.DAY_OF_YEAR)-d1.get(Calendar.DAY_OF_YEAR);
    Calendar d1p=Calendar.getInstance();
    d1p.setTime(d1.getTime());
    for (;d1p.get(Calendar.YEAR)

This assumes d0 is later than d1. If that's not guaranteed, you could always test and swap them.

Basic principle is to take the difference between the day of the year of each. If they're in the same year, that would be it.

But they might be different years. So I loop through all the years between them, adding the number of days in a year. Note that getActualMaximum returns 366 in leap years and 365 in non-leap years. That's why we need a loop, you can't just multiply the difference between the years by 365 because there might be a leap year in there. (My first draft used getMaximum, but that doesn't work because it returns 366 regardless of the year. getMaximum is the maximum for ANY year, not this particular year.)

As this code makes no assumptions about the number of hours in a day, it is not fooled by daylight savings time.