CODEWITHSUNDEEP
javadate
Farhan Syed
Farhan Syed

Reputation: 326

Finding days difference in java

After consulting a few forums, I ended up using the code below to find the days difference. But, I see a problem with the logic (may be it's my over sight?). I see that for days difference between 11 to 14 and 11 to 15 is same. How is it possible?

Date createdDate = new Date((2013 + 1900), (1 + 1), 11);
Date expirationDate = new Date((2013 + 1900), (1 + 1), 11);
for (int i = 11; i < 20; i++) {
    expirationDate.setDate(i);

    System.out.println("11 to " + i + " = "
            + (int) (expirationDate.getTime() - createdDate.getTime())
            / (1000 * 60 * 60 * 24));
}

The output is:

11 to 11 = 0
11 to 12 = 1
11 to 13 = 2
11 to 14 = 3
11 to 15 = 3
11 to 16 = 4
11 to 17 = 5
11 to 18 = 6
11 to 19 = 7

Upvotes: 1

Views: 727

Answers (5)

Radio Rogal
Radio Rogal

Reputation: 457

1000 * 60 * 60 * 24 is wrong way to find day difference. You can use JodaTime but there is a pure java solution.

Let we have two inialized variables

Calendar firstDay = ...;
Calendar secondDay = ...;

and

firstDay.before(lastDay)

is true.

Run

int firstDayNo = firstDay.get(Calendar.DAY_OF_YEAR);
int secondDayNo = secondDay.get(Calendar.DAY_OF_YEAR);
int dayDifference, yearMultiplier;

dayDifference = -firstDayNo;
yearMultiplier = secondDay.get(Calendar.YEAR) - firstDay.get(Calendar.YEAR);
while (yearMultiplier > 0) {
    dayDifference += firstDay.getActualMaximum(Calendar.DAY_OF_YEAR);
    firstDay.add(Calendar.YEAR, 1);
    yearMultiplier--;
}
dayDifference += secondDayNo;

return dayDifference;

Upvotes: 1

Evgeniy Dorofeev
Evgeniy Dorofeev

Reputation: 135992

At least in the current version your code prints correct results

11 to 11 = 0
11 to 12 = 1
11 to 13 = 2
11 to 14 = 3
11 to 15 = 4
11 to 16 = 5
11 to 17 = 6
11 to 18 = 7
11 to 19 = 8

Nevertheless new Date((2013 + 1900), (1 + 1), 11); is incorrect, in fact it is 5813-03-01. It should be new Date((2013 - 1900), (1 - 1), 11); see Date(int year, int month, int day) API 

Parameters:
year - the year minus 1900.
month - the month between 0-11.
date - the day of the month between 1-31.

Upvotes: 0

Farhan Syed
Farhan Syed

Reputation: 326

Using float, I see the problem. Using timestamp doesn't seem like a good approach to finding the days difference between 2 dates.

11 to 11 = 0.0
11 to 12 = 1.0
11 to 13 = 2.0
11 to 14 = 3.0
11 to 15 = 3.9583333
11 to 16 = 4.9583335
11 to 17 = 5.9583335
11 to 18 = 6.9583335
11 to 19 = 7.9583335

Going forward, I find the most conclusive way to determine the date difference as

Calendar cre_calendar = new GregorianCalendar((2013), (1), 11);
        Calendar exp_calendar = new GregorianCalendar((2013), (1), 19);
        Calendar maxDays = new GregorianCalendar(((2013)), (12), 31);

        if (exp_calendar.get(Calendar.DAY_OF_YEAR) < cre_calendar
                .get(Calendar.DAY_OF_YEAR)) {
            System.out
                    .println((exp_calendar.get(Calendar.DAY_OF_YEAR) + maxDays
                            .get(Calendar.DAY_OF_YEAR))
                            - cre_calendar.get(Calendar.DAY_OF_YEAR));
        } else {
            System.out.println((exp_calendar.get(Calendar.DAY_OF_YEAR))
                    - cre_calendar.get(Calendar.DAY_OF_YEAR));
        }

Upvotes: 0

PermGenError
PermGenError

Reputation: 46398

Date(year,day, month ) constructor is deprecated. i would simply use Calendars methods to get the difference between two days:

Calendar cal1=Calendar.getInstance();
Calendar cal2=Calendar.getInstance();
cal1.setTime(createdDate);
cal2.setTime(expirationDate);
System.out.println(cal2.get(Calendar.DAY_OF_MONTH )-cal1.get(Calendar.DAY_OF_MONTH ) );

EDIT:

Calendar cal1 = Calendar.getInstance();
cal1.set(2013, 2, 11);
Calendar cal2 = Calendar.getInstance();
cal2.set(2013, 2, 11);
for (int i = 11; i < 20; i++) {
 cal2.set(Calendar.DATE, i);
    System.out.println("11 to " + i + " = " + (cal2.get(Calendar.DAY_OF_MONTH) -cal1.get(Calendar.DAY_OF_MONTH)));
}

OUTPUT:

11 to 11 = 0
11 to 12 = 1
11 to 13 = 2
11 to 14 = 3
11 to 15 = 4
11 to 16 = 5
11 to 17 = 6
11 to 18 = 7
11 to 19 = 8

Upvotes: 1

Matt Ball
Matt Ball

Reputation: 359776

Use Joda Time's Days#daysBetween(). There is no better way.

DateMidnight createdDate = new DateMidnight(2013, 2, 11);

for (int i = 11; i < 20; i++) {

    DateMidnight expirationDate = new DateMidnight(2013, 2, i);
    int dayDifference = Days.daysBetween(createdDate, expirationDate);

    System.out.println("11 to " + i + " = " + dayDifference);
}

Upvotes: 4

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