Unparseable date with extra number in Java

Question

What's wrong in this code? I'm trying to parse a date format that has 0 between years and months.

import java.text.SimpleDateFormat;

class Main {
    public static void main(String[] args) {
        SimpleDateFormat format = new SimpleDateFormat("yyyy'0'MMdd");
        try {
            Date date = format.parse("201600101");
            System.out.println(date);
        } catch (Exception ex) {
            System.out.println(ex.getMessage());
        }
    }
}

This outputs Unparseable date: "201600101". If I change '0' to anything but number [e.g. 'X' and format.parse("2016X0101")] this will work.

Answer 1

As Peter Lawrey said Java sees '20160' as a year. You can solve your problem by modifying "201600101" to, for example, 2016-00101 and refactor your format patter as

SimpleDateFormat format = new SimpleDateFormat("yyyy-'0'MMdd");

That will parse your date.

Answer 2

Using a library where you can use fixed widths of four digits for the year would do the trick. Example for java.time-package in Java-8:

    String input = "201600101";

    DateTimeFormatter dtf =
        new DateTimeFormatterBuilder()
            .appendValue(ChronoField.YEAR, 4, 4, SignStyle.NEVER)
            .appendLiteral('0')
            .appendPattern("MMdd")
            .toFormatter();
    LocalDate date = LocalDate.parse(input, dtf);
    System.out.println(date); // 2016-01-01

This has the strong advantage not to be forced to change the input. It is always better to change the formatter. Admittingly, not possible with SimpleDateFormat.