Question

I am trying to calculate difference between two date strings both of which are taken from user through a html form in format (yyyy/MM/dd)
Code:

public boolean diffDate() throws ParseException
 {
     date1 = getissuedate();
     date2 = getduedate();
         Calendar cal1 = Calendar.getInstance();
    Calendar cal2 = Calendar.getInstance();
    SimpleDateFormat formatter1 = new SimpleDateFormat("yyyy/MM/dd");
    SimpleDateFormat formatter2 = new SimpleDateFormat("yyyy/MM/dd"); 
Date date_old = formatter1.parse(date1);
Date date_new = formatter2.parse(date2);
long milis1 = date_old.getTime();
long milis2 = date_new.getTime();

long diff = milis2 - milis1;       

    if( diff<3 || diff>3)
    {
        return true;
    }
    else 
    {       
        return false;
    }       
 }

Now am using an if condition to report error in my webpage if difference between the date is not equal to 3.
Code:

try {
        if(diffDate())
        {
            errors.add("duedate", new ActionMessage("error.duedate.required"));
        }
    } catch (ParseException ex) {
        Logger.getLogger(IssueBookForm.class.getName()).log(Level.SEVERE, null, ex);
    }

where error.duedate.required is mapped to “check date”

So, the issue is “check date” error is printed for any value of both date string.

Answer 1

you’ll never get a difference of exactly 3 milliseconds between two dates gotten from a yyyy/MM/dd formatted string (maximum accuracy will be 24 hours)

if you want 3 days difference use 24*60*60*1000 for a factor to scale the values