This is NOT my work, found the answer here. did not want a broken link in the future :).
The key is this line for taking daylight setting into account, ref Full Code.
TimeZone.setDefault(TimeZone.getTimeZone("Europe/London"));
or try passing TimeZone as a parameter to daysBetween() and call setTimeZone() in the sDate and eDate objects.
So here it goes:
public static Calendar getDatePart(Date date){
Calendar cal = Calendar.getInstance(); // get calendar instance
cal.setTime(date);
cal.set(Calendar.HOUR_OF_DAY, 0); // set hour to midnight
cal.set(Calendar.MINUTE, 0); // set minute in hour
cal.set(Calendar.SECOND, 0); // set second in minute
cal.set(Calendar.MILLISECOND, 0); // set millisecond in second
return cal; // return the date part
}
getDatePart() taken from here
/**
* This method also assumes endDate >= startDate
**/
public static long daysBetween(Date startDate, Date endDate) {
Calendar sDate = getDatePart(startDate);
Calendar eDate = getDatePart(endDate);
long daysBetween = 0;
while (sDate.before(eDate)) {
sDate.add(Calendar.DAY_OF_MONTH, 1);
daysBetween++;
}
return daysBetween;
}
The Nuances:
Finding the difference between two dates isn't as straightforward as subtracting the two dates and dividing the result by (24 * 60 * 60 * 1000). Infact, its erroneous!
For example: The difference between the two dates 03/24/2007 and 03/25/2007 should be 1 day; However, using the above method, in the UK, you'll get 0 days!
See for yourself (code below). Going the milliseconds way will lead to rounding off errors and they become most evident once you have a little thing like Daylight Savings Time come into the picture.
Full Code:
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;
public class DateTest {
public class DateTest {
static SimpleDateFormat sdf = new SimpleDateFormat("dd-MMM-yyyy");
public static void main(String[] args) {
TimeZone.setDefault(TimeZone.getTimeZone("Europe/London"));
//diff between these 2 dates should be 1
Date d1 = new Date("01/01/2007 12:00:00");
Date d2 = new Date("01/02/2007 12:00:00");
//diff between these 2 dates should be 1
Date d3 = new Date("03/24/2007 12:00:00");
Date d4 = new Date("03/25/2007 12:00:00");
Calendar cal1 = Calendar.getInstance();cal1.setTime(d1);
Calendar cal2 = Calendar.getInstance();cal2.setTime(d2);
Calendar cal3 = Calendar.getInstance();cal3.setTime(d3);
Calendar cal4 = Calendar.getInstance();cal4.setTime(d4);
printOutput("Manual ", d1, d2, calculateDays(d1, d2));
printOutput("Calendar ", d1, d2, daysBetween(cal1, cal2));
System.out.println("---");
printOutput("Manual ", d3, d4, calculateDays(d3, d4));
printOutput("Calendar ", d3, d4, daysBetween(cal3, cal4));
}
private static void printOutput(String type, Date d1, Date d2, long result) {
System.out.println(type+ "- Days between: " + sdf.format(d1)
+ " and " + sdf.format(d2) + " is: " + result);
}
/** Manual Method - YIELDS INCORRECT RESULTS - DO NOT USE**/
/* This method is used to find the no of days between the given dates */
public static long calculateDays(Date dateEarly, Date dateLater) {
return (dateLater.getTime() - dateEarly.getTime()) / (24 * 60 * 60 * 1000);
}
/** Using Calendar - THE CORRECT WAY**/
public static long daysBetween(Date startDate, Date endDate) {
...
}
OUTPUT:
Manual - Days between: 01-Jan-2007 and 02-Jan-2007 is: 1
Calendar - Days between: 01-Jan-2007 and 02-Jan-2007 is: 1
Manual - Days between: 24-Mar-2007 and 25-Mar-2007 is: 0
Calendar - Days between: 24-Mar-2007 and 25-Mar-2007 is: 1
