SimpleDateFormat problems with 2 year date

Question

I\'m trying to understand two things:

1. Why doesn\'t the following code throw an exception (since the SimpleDateFormat is not lenient)
2. It d

Answer 1

SimpleDateFormat API:

For parsing, if the number of pattern letters is more than 2, the year is interpreted literally, regardless of the number of digits. So using the pattern "MM/dd/yyyy", "01/11/12" parses to Jan 11, 12 A.D.

As for lenient, when it's set to false parse throws exception for invalid dates, eg 01/32/12, while in lenient mode this date is treated as 02/01/12. SimpleDateFormat uses Calendar internally, details about leniency can be found in Calendar API.

Answer 2

Question 1. This is a partial duplicate of Why Does Java's SimpleDateFormat parse this. The second answer on the question answers this nicely. The crux of it is this:

Number: For parsing, the number of pattern letters is ignored unless it's needed to separate two adjacent fields. Year: During parsing, only strings consisting of exactly two digits […] will be parsed into the default century. Any other numeric string, such as a one digit string, a three or more digit string, or a two digit string that isn't all digits (for example, "-1"), is interpreted literally. So "01/02/3" or "01/02/003" are parsed, using the same pattern

Question 2. Look carefully: your input format is not the same as the format that you are passing to the function.

new SimpleDateFormat("dd/MM/yyyy");

vs.

format.parse("01/01/13");

Either parse to 01/01/2013 or use the date forat 'dd/MM/yy'.

Answer 3

java.time

Use java.time, the modern Java date and time API, and the exception you expected comes sure thing:

    DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
    String strToParse = "01/01/13";
    LocalDate date = LocalDate.parse(strToParse, dateFormatter);

Result:

Exception in thread "main" java.time.format.DateTimeParseException: Text '01/01/13' could not be parsed at index 6
  at java.base/java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:2046)
  at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1948)
  at java.base/java.time.LocalDate.parse(LocalDate.java:428)

If you scroll right, you will see that the exception message mentions “could not be parsed at index 6”. Index 6 in the string is where the two digit year stands where four digits were expected.

When this question was asked nearly 7 years ago, using SimpleDateFormat and Date was acceptable. They were always poorly designed, and their replacement came out 7 months after the question was asked, so they are now considered long outdated. I warmly recommend using java.time instead.

Link

Oracle tutorial: Date Time explaining how to use java.time.

Answer 4

According to the SimpleDateFormat javadoc for JDK 1.6,

For parsing, the number of pattern letters is ignored unless it's needed to separate two adjacent fields.

A look at the source code for the method that does the work, SimpleDateFormat.parse(String, ParsePosition), confirms this. There is a variable obeyCount that is true if the pattern has no delimiters, like "yyyyMMdd", and false otherwise. With your pattern the parser looks for 3 numbers separated by 2 delimiters and does not care about the number of digits in each position.

The answers to your questions:

1. Lenient is not a factor when delimiters are used.
2. You did not call SimpleDateFormat.set2DigitYearStart so why should the code do what you didn't tell it to do?