Y returns 2012 while y returns 2011 in SimpleDateFormat

Question

I wonder why \'Y\' returns 2012 while \'y\' returns 2011 in SimpleDateFormat:

System.out.println(new SimpleDateFormat(\"Y\").format(new Date()))         


        

Answer 1

I convert a date back and forth - you would expect the same year when you do this.

Notice how it advances one!

This is bad: YYYY!

You can run it here.

import java.util.Date;
import java.text.SimpleDateFormat;
import java.text.ParseException;
import static java.lang.System.out;
class Playground {
    public static Date convertYYYYMMDDStr(String s) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        Date result = null;
        try {
            result = sdf.parse(s);
        } catch(ParseException e) {
            e.printStackTrace();
        }
        return result;
    }
    public static String formatDateToStrWithSDF(Date d, SimpleDateFormat s) {
        return s.format(d);
    }
    public static void main(String[ ] args) {
        // DON'T DO. Use yyyy instead of YYYY
        SimpleDateFormat sdfdmy = new SimpleDateFormat("dd-MM-YYYY"); 
        String jan1st2020sb = "2020-01-01";
        Date jan1st2020d = convertYYYYMMDDStr(jan1st2020sb);
        String jan1st2020sa = formatDateToStrWithSDF(jan1st2020d, sdfdmy);
        out.println(jan1st2020sb);
        out.println(jan1st2020d);
        out.println(jan1st2020sa);
        String dec31st2020sb = "2020-12-31";
        Date dec31st2020d = convertYYYYMMDDStr(dec31st2020sb);
        String dec31st2020sa = formatDateToStrWithSDF(dec31st2020d, sdfdmy);
        out.println(dec31st2020sb);
        out.println(dec31st2020d);
        out.println(dec31st2020sa);
    }
}

This is good: yyyy