Strange behavior of SimpleDateFormat

Question

I am using SimpleDateFormat like this:

SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd-HH:mm:ss.SSS");
Date result = sdf.parse("20221114-12:34:56.789");

Works fine for the above example (result: Mon Nov 14 12:34:56 CET 2022 ), but works strange for obvious erroneous input:

• 123-20221114-12:34:56.789 -> Sun Feb 15 12:34:56 CET 728
• 12320221114-12:34:56.789 -> Mon Nov 21 12:34:56 CET 1289

I would expect to throw ParseException in these cases.

Note that the timestamp is input and the format cannot be changed.

As a cross-check I tried this: abc-20221114-12:34:56.789 , and at least in this case it threw ParseException .

Answer 1

The terrible SimpleDateFormat class was years ago supplanted by the modern java.time classes, specifically DateTimeFormatter .

DateTimeFormatter f = DateTimeFormatter.ofPattern ( "uuuuMMdd-HH:mm:ss.SSS" );
LocalDateTime result = LocalDateTime.parse( "20221114-12:34:56.789" , f );

Answer 2

The SimpleDateFormat contains bugs. In the example posted the interpretations are the following:

• 123-20221114-12:34:56.789 : year 123, month -2, day 221114
• 12320221114-12:34:56.789 : year 1232, month 02, day 21114

Actually this answers the original question. And as a suggestion the java.time module should be used introduced in Java 8, as described in other comments.