[Android, Java] Method to find the elapsed date from two dates

Thing you want to do

Obtain the elapsed date (such as 0 years, 0 months, 0 days) from the two dates. Example 2020/08/01 and 2020/08/03 → 0 years 0 months 2 days 2020/08/01 and 2020/09/01 → 0 years, 1 month, 0 days 2020/08/01 and 2021/08/01 → 1 year 0 months 0 days

specification

-From date> To date returns an error (error code: -1) ・ Date format is yyyy / MM / dd only -From date and To date are both String type ・ Return year, month, and day with int [](0: year, 1: month, 2: day)

Implementation

    public static int getDateDiff(String paraFromDate, String paraToDate, int[] paraDiffDay) {
        int     diffYear = 0 ;
        int     diffMonth = 0 ;
        int     diffDay = 0 ;

        //Break down the date of the start date into year, month, and day(From)
        int     from_year = parseInt(paraFromDate.substring(0,4)) ;
        int     from_month = parseInt(paraFromDate.substring(5,7)) ;
        int     from_day = parseInt(paraFromDate.substring(8,10)) ;

        //Break down the base date into year, month, and day(To)
        int     to_year = parseInt(paraToDate.substring(0,4)) ;
        int     to_month = parseInt(paraToDate.substring(5,7)) ;
        int     to_day = parseInt(paraToDate.substring(8,10)) ;

        Calendar comp_from = Calendar.getInstance() ;
        comp_from.set(from_year, from_month - 1, from_day) ;

        Calendar comp_to = Calendar.getInstance() ;
        comp_to.set(to_year, to_month - 1, to_day) ;

        //Starting date>If it is a base date, make an error
        if(comp_from.compareTo(comp_to) > 0) {
            return -1;
        }

        //Get the year difference
        diffYear = to_year - from_year ;

        //Compare months
        if(from_month > to_month) {
            //When the month of the starting date is larger=Across the year
            to_month = to_month + 12 ;
            //Minus year
            //If it is the same year from_The month can never be bigger, so it can't be negative
            diffYear = diffYear - 1 ;
        }

        //Get the difference between the months
        diffMonth = to_month - from_month ;

        //Compare days
        //Starting date(From)If is larger, it is judged that it straddles the moon
        if(from_day > to_day) {
            //Add the maximum number of start dates
            to_day = to_day + comp_from.getActualMaximum(comp_from.DATE) ;
            //Minus the difference between the months
            diffMonth = diffMonth - 1 ;
        }
        //Get the difference between days
        diffDay = to_day - from_day ;

        //Set in argument
        paraDiffDay[0] = diffYear ;
        paraDiffDay[1] = diffMonth ;
        paraDiffDay[2] = diffDay ;

        return 0 ;

    }

Caller

    String fromDate = '2020/08/20' ;
    String toDate = '2020/10/01' ;
    int diffDate[] = {0,0,0} ;
    if( getDateDiff(fromDate, toDate, diffDate) != 0 ) {
        //error
    }
    else {
        String keikaDate = diffDate[0] + "Year" + diffDate[1] + "Months" + diffDate[2] + "Day" ;
    }
    

Problems, issues

・ No error handling → Exception occurs if the argument date is not in the format of yyyy / MM / dd → If the date does not exist even if it is in yyyy / MM / dd format, the behavior is incorrect.

good point

-Get the maximum number of days in the month using getActualMaximum → At first 31st in January, 3,5,7,8,10, December 30th in April, June, September and November February was 29 days in leap years, 28 days otherwise. Solved with a sentence of getActualMaximum.