Question

I am tryig to convert birthday from String to Date in order to add to the arraylist contacts. Then read from the contacts to display the birthday. However 05/02/1990 becomes 365/12/1990, 06/12/1991 becomes 365/12/1991 (i.e. DD and MM are incorrect). Thank you very much for the help!

ArrayList<Person> contacts = new ArrayList<Person>();
...
String firstName = sc.next();
String lastName = sc.next();
String email = sc.next();
String birthdayStr = sc.next();
SimpleDateFormat formatter = new SimpleDateFormat("DD/MM/YYYY");
try{

    Date birthday = formatter.parse(birthdayStr); 
    Person s = new Person(firstName, lastName, email, birthday);
    contacts.add(s);
    Date b = s.getBirthday();
    System.out.println(formatter.format(b));

}catch(ParseException e){

   System.out.println( e.getMessage());
}

Answer 1

D is day in year, you need lowercase d for day of month. Use lowercase y also.

new SimpleDateFormat("dd/MM/yyyy")

The use of uppercase Y relates to week year:

A week year is in sync with a WEEK_OF_YEAR cycle. All weeks between the first and last weeks (inclusive) have the same week year value. Therefore, the first and last days of a week year may have different calendar year values.

For example, January 1, 1998 is a Thursday. If getFirstDayOfWeek() is MONDAY and getMinimalDaysInFirstWeek() is 4 (ISO 8601 standard compatible setting), then week 1 of 1998 starts on December 29, 1997, and ends on January 4, 1998. The week year is 1998 for the last three days of calendar year 1997. If, however, getFirstDayOfWeek() is SUNDAY, then week 1 of 1998 starts on January 4, 1998, and ends on January 10, 1998; the first three days of 1998 then are part of week 53 of 1997 and their week year is 1997.

To avoid this "side effect" on the year, lowercase y can be used.