Comparing two Dates in Java

Question

I have an Identity class with necessary accessors and mutators.

In a seperate program I am comparing the Identity's Date to todays date which always returns <= 10. However when I go to print it I get the same result no matter what the date is. Is there a different way to access the correct date?

I need to get the number of days between two dates and I'm having trouble on the formating:

Date today = new Date();
        DateFormat df = new SimpleDateFormat("MM/dd/yyyy");

        Date a = df.parse("06/18/2015");
        Date b = df.parse("01/04/2015");
        Date c = df.parse("02/04/2015"); 
        Date d = df.parse("03/04/2015"); 
        Date e = df.parse("07/04/2015"); 
if(a.compareTo(today) == 30{
//do stuff
}

I've tried multiple methods to no avail.

@SotiriosDelimanolis Returns: the value 0 if the argument Date is equal to this Date; a value less than 0 if this Date is before the Date argument; and a value greater than 0 if this Date is after the Date argument. -- To me this returns the difference between them but i could be wrong — BarryDale2014
– BarryDale2014, Commented Dec 4, 2014 at 17:21
It says 0, greater or lower. That is not the same as the difference between the two dates. — Tobías
– Tobías, Commented Dec 4, 2014 at 17:25

Julien R · Accepted Answer · 2014-12-04 18:00:30Z

1

You have two mistakes in your code :

compareTo() will only return 0 if dates are identical, a positive value if the date is after the argument, or a negative value if it is before. It does not return the difference between the two dates. To get the difference you can write :

today.getTime() - expiration.getTime()

to get the number of milliseconds between the two dates, and then compare it to 10 days converted in milliseconds.
You don't initialize your date correctly : Date a = new Date(06/18/2015); won't work. It is supposed to create a new Date with a number of milliseconds as a parameter. So your code will divide 6 by 18 and by 2015 to obtain a number of milliseconds... You can use :

Date a = new GregorianCalendar(2015, 06, 18).getTime();
You have a simpler way to get today : Date today = new Date();

edited Dec 4, 2014 at 18:00

answered Dec 4, 2014 at 17:25

Julien R

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Community · Accepted Answer · 2017-05-23 11:57:43Z

0

You're performing integer division, not calling the Date constructor you think.

Date a = new Date(06/18/2015);

Use a DateFormat like

public static void main(String[] args) {
    DateFormat df = new SimpleDateFormat("MM/dd/yyyy");
    try {
        Date a = df.parse("06/18/2015");
        System.out.println("1. " + a);
        System.out.println("2. " + df.format(a));
    } catch (ParseException e) {
        e.printStackTrace();
    }
}

Note Date is an instant in time, so it's default textual representation may vary from what you might expect. See the differences in lines 1 and 2 below,

1. Thu Jun 18 00:00:00 EDT 2015
2. 06/18/2015

Finally, you need to calculate the difference between two dates. compareTo will tell you smaller or bigger, not magnitude.

edited May 23, 2017 at 11:57

CommunityBot

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answered Dec 4, 2014 at 17:38

Elliott Frisch

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Comments

BarryDale2014 · Accepted Answer · 2014-12-10 19:03:54Z

0

I made a method that takes in two dates, converts them and returns a long that works fine. 86400000 is the number of milliseconds in a day. I am using GregorianCalendar format

public long compareDates(Date exp, Date today){

         return (exp.getTime()-today.getTime())/86400000;
    }

edited Dec 10, 2014 at 19:03

answered Dec 4, 2014 at 20:12

BarryDale2014

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2 Comments

Julien R Over a year ago

I'm not sure to understand what you're trying to do. Why do you substract one day to each date before converting it? If your goal is to get the number of days between the two dates, you can simply write : return Maths.abs(exp.getTime()-today.getTime())/86400000 (Math.abs is here to always return a positive value as the difference could be negative)

BarryDale2014 Over a year ago

@JulienR that's what I ended up doing without the Math.abs. A seperate function will be implemented if indeed there is a negative value

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