Validating Leap Years

Question

Is there a way of checking that an entered leap year date is valid?
Eg. User enters 2/29/2001 which is not a valid date because 2001 was not a leap year.

Answer 1

You should be able to use the SimpleDateFormat class to do this by issuing a setLenient(false) call. However, it does not seem to detect a leap year problem with the date 2/29. If you run the code below, you'll see that in the first section it correctly detects that 2/30 is a bad date, but in the second section, it does not detect 2/29 as a bad date. In section 3, you can see how an added test can detect the problem date.
        //Date validation
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        //Section 1 - correctly detects bad date
        try {
            String date = "2001-02-30";
            System.out.println("Here's the date - " + sdf.parse(date));
            sdf.setLenient(false);
            System.out.println("Here's the date - " + sdf.parse(date));
        } catch (ParseException pe) {
            System.out.println("Bad date");
        //Section 2 - does not detect bad date
        try {
            String date = "2001-02-29";
            System.out.println("Here's the date - " + sdf.parse(date));
            sdf.setLenient(false);
            System.out.println("Here's the date - " + sdf.parse(date));
        } catch (ParseException pe) {
            System.out.println("Bad date");
        //Section 3 - correctly detects bad date with additional check
        try {
            String date = "2001-02-29";
            System.out.println("Here's the date - " + sdf.parse(date));
            sdf.setLenient(false);
            //Additional test to compensate for leap year failure
            String dateString = sdf.format(sdf.parse(date));
            if (!dateString.equals(date)) {
                System.out.println("Bad date");
            } else {
                System.out.println("Here's the date - " + sdf.parse(date));
        } catch (ParseException pe) {
            System.out.println("Bad date");
        }