I want to calculate the difference of days between two dates. My code works fine when the year of the date does not change, but when I calculate the difference between two dates like so: (13/01/2012 to 13/12/2011), it gives a negative value. It also gives wrong values of difference when I calculate the difference between today's date and a future date. Please help me. Thank you in advance. Here is my code:
//getting values from text box
String fromtext = from.getText().toString();
String totext = to.getText().toString();
//sdf if a simple date formatter
SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
Date fromdate = (Date) sdf.parse(fromtext);
Date todate = (Date) sdf.parse(totext);
Calendar fromcal = Calendar.getInstance();
Calendar tocal = Calendar.getInstance();
fromcal.setTime(fromdate);
tocal.setTime(todate);// setting to date
int reportDays=(int)(todate.getTime()-fromdate.getTime())/(3600*24*1000);
please tell me what is the best way to calculate the difference in days.
Dates input : 13/01/2012
, 13/12/2011
format seems dd/MM/yyyy
and you are using wrong one (ie MM/dd/yyyy
)
ChronoUnit.DAYS.between(
LocalDate.parse( "13/01/2012" , DateTimeFormatter.ofPattern( "dd/MM/uuuu" ) ) ,
LocalDate.parse( "13/12/2011" , DateTimeFormatter.ofPattern( "dd/MM/uuuu" ) )
)
Much easier with the modern java.time classes that supplant the troublesome old legacy date-time classes such as Date
& Calendar
.
(13/01/2012 to 13/12/2011),
The LocalDate
class represents a date-only value without time-of-day and without time zone.
DateTimeFormatter f = DateTimeFormatter.ofPattern( "dd/MM/uuuu" );
LocalDate start = LocalDate.parse( "13/01/2012" , f );
LocalDate stop = LocalDate.parse( "13/12/2011" , f );
Use ChronoUnit
to calculate elapsed days.
long days = ChronoUnit.DAYS.between( start , stop );
Of course the number of days is negative when going back in time. Notice how your stop date is earlier than your start date.
A time zone is crucial in determining a date. For any given moment, the date varies around the globe by zone. For example, a few minutes after midnight in Paris France is a new day while still “yesterday” in Montréal Québec .
Specify a proper time zone name in the format of continent/region
, such as America/Montreal
, Africa/Casablanca
, or Pacific/Auckland
. Never use the 3-4 letter abbreviation such as EST
or IST
as they are not true time zones, not standardized, and not even unique(!).
ZoneId z = ZoneId.of( "America/Montreal" );
LocalDate today = LocalDate.now( z );
You can use ChronoUnit
again to count days into the future.
long days = ChronoUnit.DAYS.between( today , today.plusMonths( 7 ) );
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date
, Calendar
, & SimpleDateFormat
.
The Joda-Time project, now in maintenance mode , advises migration to the java.time classes.
To learn more, see the Oracle Tutorial . And search Stack Overflow for many examples and explanations. Specification is JSR 310 .
Where to obtain the java.time classes?
The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval
, YearWeek
, YearQuarter
, and more .
I think you should try better googling....
In addition to the format issue already mentionned, you are likely to have an overflow. Try this:
int reportDays=(int)((todate.getTime()-fromdate.getTime())/(3600*24*1000));
I would do it like this!
package javaapplication2;
//@author Ibrahim Yesilay
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Scanner;
public class JavaApplication2 {
public static void main(String[] args) throws ParseException {
Scanner scan = new Scanner(System.in);
System.out.println("First dates Day :");
int d = scan.nextInt();
System.out.println("First dates Mounth :");
int m = scan.nextInt();
System.out.println("First dates Year :");
int y = scan.nextInt();
String date;
date = Integer.toString(d) + "/" + Integer.toString(m) + "/" + Integer.toString(y);
SimpleDateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy");
Date firstdate = null;
firstdate = dateFormat.parse(date);
System.out.println(dateFormat.format(firstdate));
System.out.println("Second dates Day :");
d = scan.nextInt();
System.out.println("Second dates Month :");
m = scan.nextInt();
System.out.println("Second dates Year :");
y = scan.nextInt();
date = Integer.toString(d) + "/" + Integer.toString(m) + "/" + Integer.toString(y);
Date seconddate = null;
seconddate = dateFormat.parse(date);
System.out.println(dateFormat.format(seconddate));
if (seconddate.getTime() > firstdate.getTime()) {
long sonuc = (long)(seconddate.getTime()- firstdate.getTime())/(3600*24*1000);
System.out.println("" + sonuc);
} else if (firstdate.getTime() > seconddate.getTime()) {
long sonuc = (long)(firstdate.getTime()- seconddate.getTime())/(3600*24*1000);
System.out.println("" + sonuc);
} else {
System.out.println("The dates are equal!");
}
}
}
使用joda时间将是最简单的方法。
check this code:
import java.util.Calendar;
public class DateDifferent{
public static void main(String[] args){
Calendar calendar1 = Calendar.getInstance();
Calendar calendar2 = Calendar.getInstance();
calendar1.set(2007, 01, 10);
calendar2.set(2007, 07, 01);
long milliseconds1 = calendar1.getTimeInMillis();
long milliseconds2 = calendar2.getTimeInMillis();
long diff = milliseconds2 - milliseconds1;
long diffSeconds = diff / 1000;
long diffMinutes = diff / (60 * 1000);
long diffHours = diff / (60 * 60 * 1000);
long diffDays = diff / (24 * 60 * 60 * 1000);
System.out.println("\nThe Date Different Example");
System.out.println("Time in milliseconds: " + diff + " milliseconds.");
System.out.println("Time in seconds: " + diffSeconds + " seconds.");
System.out.println("Time in minutes: " + diffMinutes + " minutes.");
System.out.println("Time in hours: " + diffHours + " hours.");
System.out.println("Time in days: " + diffDays + " days.");
}
}
Here's a simple little class I wrote for this purpose:
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class DifferenceInDays
{
public int dateOffset(String incomingDate) throws ParseException
{
// parse dates
DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
Date date = (Date) formatter.parse(incomingDate);
// convert to milliseconds
long millisecs = date.getTime();
// convert to days
int offsetInDays = (int) Math.abs(millisecs / (1000 * 60 * 60 * 24));
return offsetInDays;
}
}
It takes care of negative offsets using the absolute value method.
If you try this with a locale that has daylight saving, and the from and to dates are before and after a daylight saving change the result may be different by 1 day. This is because Date
and Calendar
use timezones.
If you are only going to be dealing with dates between the years 1900 and 2100, there is a simple calculation which will give you the number of days since 1900:
public static int daysSince1900(Date date) {
Calendar c = new GregorianCalendar();
c.setTime(date);
int year = c.get(Calendar.YEAR);
if (year < 1900 || year > 2099) {
throw new IllegalArgumentException("daysSince1900 - Date must be between 1900 and 2099");
}
year -= 1900;
int month = c.get(Calendar.MONTH) + 1;
int days = c.get(Calendar.DAY_OF_MONTH);
if (month < 3) {
month += 12;
year--;
}
int yearDays = (int) (year * 365.25);
int monthDays = (int) ((month + 1) * 30.61);
return (yearDays + monthDays + days - 63);
}
Thus, to get the difference in days between two dates, you calculate their days since 1900 and calc the difference. Our daysBetween method looks like this:
public static Integer getDaysBetween(Date date1, Date date2) {
if (date1 == null || date2 == null) {
return null;
}
int days1 = daysSince1900(date1);
int days2 = daysSince1900(date2);
if (days1 < days2) {
return days2 - days1;
} else {
return days1 - days2;
}
}
And don't ask me where this calculation came from because we've used it since the early '90s.
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