Question

I have written a small method to return a date object when given a string. The method is as shown below:

public Date getDateObjectFromString(String dateAsString)
{
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ");
    Date tempDate = null;

    try
    {
        tempDate = sdf.parse(dateAsString);
    }
    catch(ParseException pe)
    {
        //do some error reporting here
    }
    return tempDate;
}

Everything is working ok, but I’ve run into something that I’d like to clarify. When I pass two different strings to this method it is returning the same date when reading the value in the debugger. The two strings I am passing are:

2011-07-21T19:44:00.000-0400

2011-07-21T19:44:00.000-04:00

As you can see these two strings are nearly identical, and when I look at the variable output for these newly created dates in the debugger, it shows the exact same date/time for either string. So, does the colon in the second string (at 04:00) make any difference if the debugger is showing the same date? Should I worry or can I proceed without any weird bugs popping up later on?

Answer 1

The Android docs for SimpleDateFormat mention that they use RFC 822 timezones. When I went to the JavaDocs for SimpleDateFormat, which is what Android is attempting to mimic with this class, I see this note about RFC 822 timezones:

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

 RFC822TimeZone:
         Sign TwoDigitHours Minutes
 TwoDigitHours:
         Digit Digit

TwoDigitHours must be between 00 and 23. Other definitions are as for
general time zones. For parsing, general time zones are also
accepted.

And here is the note for general time zones:

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

Hours must be between 0 and 23, and Minutes must be between 00 and 59.
The format is locale independent and digits must be taken from the
Basic Latin block of the Unicode standard.

In the definition for the general time zones, you will notice they use a ‘:’.

This means that your two strings, while different, will be parsed to the same time.

1. RFC 822 –> 2011-07-21T19:44:00.000-0400
2. General –> 2011-07-21T19:44:00.000-04:00