SimpleDateFormat class introduction

SimpleDateFormat is a concrete class for formatting and parsing dates in a locale-sensitive manner. It allows for formatting date to text, parsing from text to date, and normalization.

Date and Time Patterns

Pattern letters are usually repeated, as their number determines the exact presentation:

1. Text:For formatting, if the number of pattern letters is 4 or more, the full form is used; otherwise a short or abbreviated form is used if available. For parsing, both forms are accepted, independent of the number of pattern letters.
2. Number:For formatting, the number of pattern letters is the minimum number of digits, and shorter numbers are zero-padded to this amount. For parsing, the number of pattern letters is ignored unless it's needed to separate two adjacent fields.
3. Month:If the number of pattern letters is 3 or more, the month is interpreted as text; otherwise, it is interpreted as a number.
4. Year:If the formatter's Calendar is the Gregorian calendar, the following rules are applied.
   1. For formatting, if the number of pattern letters is 2, the year is truncated to 2 digits; otherwise it is interpreted as a number.
   2. 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.
   3. For parsing with the abbreviated year pattern ("y" or "yy"), SimpleDateFormat must interpret the abbreviated year relative to some century. It does this by adjusting dates to be within 80 years before and 20 years after the time the SimpleDateFormat instance is created. For example, using a pattern of "MM/dd/yy" and a SimpleDateFormat instance created on Jan 1, 1997, the string "01/11/12" would be interpreted as Jan 11, 2012 while the string "05/04/64" would be interpreted as May 4, 1964. During parsing, only strings consisting of exactly two digits, as defined by Character#isDigit(char), 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, as Jan 2, 3 AD. Likewise, "01/02/-3" is parsed as Jan 2, 4 BC.
5. General time zone: Time zones are interpreted as text if they have names. For time zones representing a GMT offset value, the following syntax is used:

            GMTOffsetTimeZone:
                    GMT Sign Hours : Minutes
            Sign: one of
                    + -
            Hours:
                    Digit
                    Digit Digit
            Minutes:
                    Digit Digit
            Digit: one of
                    0 1 2 3 4 5 6 7 8 9
       

6. RFC 822 time zone: For formatting, the RFC 822 4-digit time zone format is used:

        RFC822TimeZone:
                Sign TwoDigitHours Minutes
        TwoDigitHours:
                Digit Digit

7. ISO 8601 Time zone: The number of pattern letters designates the format for both formatting and parsing as follows:

        ISO8601TimeZone:
                OneLetterISO8601TimeZone
                TwoLetterISO8601TimeZone
                ThreeLetterISO8601TimeZone
        OneLetterISO8601TimeZone:
                Sign TwoDigitHours
                Z
        TwoLetterISO8601TimeZone:
                Sign TwoDigitHours Minutes
                Z
        ThreeLetterISO8601TimeZone:
                Sign TwoDigitHours : Minutes
                Z