Calculate the number of days passed from a given year I have this code for calculating the number of days passed from a given year:

for (int currentYear = localDate.getYear() - 1; currentYear &gt;= STARTING_YEAR; currentYear--){
            LocalDate date = LocalDate.of(currentYear,5,5); //an arbitrary day of year
            jdn += date.lengthOfYear();
        }
jdn += localDate.getDayOfYear();


This code is working as expected. 

I am not comfortable with choosing an arbitrary day to only get the length of the year. Is there any better approach?
Your code scales poorly if there are many years between STARTING_YEAR and localDate.

Worse, if localDate occurs before the STARTING_YEAR, then your code behaves as if STARTING_YEAR is the same year as localDate, which is weird behavior.

To calculate the number of days between two dates, use DAYS.between().

import java.time.LocalDate;
import static java.time.temporal.ChronoUnit.DAYS;

…    
long jdn = 1 + DAYS.between(LocalDate.ofYearDay(STARTING_YEAR, 1), localDate);


The 1 + is necessary because the convention when subtracting dates is inclusive-exclusive, whereas your code uses an inclusive-inclusive range.