parsing a date from command line

[kelly evans]

Here's my problem: the user enter's a date in the command line. I want to take that date, in whatever date format it happens to be in, and reformat it into a standard date format of: "dd-MMM-yy". Because the possibilities are endless as to what the user might enter, how do i account for so many variations? Many possible dates IN --> one OUTcome.

[Sunetra Saha]

You have to have some guidelines as to the formatting. For example - you cannot allow the user to enter dates as
dd/mm/yy
mm/dd/yy
yy/mm/dd - all at the same time. No compiler can then possibly say what 01/02/03 means.
Once you decide what are the allowable formats e.g
dd/mm/yy
dd/mm/yyyy
dd/mon/yyyy
dd/month/yyyy
All the above with - & . seperator etc. etc.
Then you have to write a method that parses for all these cases. For example you have to check the seperator chars and tokenize the string into 3 fragments. Then check value of first fragment. If it is digit and within 31(max possible value of dd) etc.
Let us know how it goes.

[Angela Lamb]

The DateFormat class has a method to parse a date string into a Date. There is no need to tokenize the string and parse it yourself, as Sunetra described.
There are 4 instances of this class that you can use: SHORT, MEDIUM, LONG, and FULL. Each instance parses several different input formats. See the API docs for more information on these formats.
I can't guarantee that there is a way to accept ALL possible inputs, but this should come pretty close:

Date inputDate = null;
DateFormat shortFormat = DateFormat.getDateInstance(DateFormat.SHORT);
DateFormat mediumFormat = DateFormat.getDateInstance(DateFormat.MEDIUM);
DateFormat longFormat = DateFormat.getDateInstance(DateFormat.LONG);
DateFormat fullFormat = DateFormat.getDateInstance(DateFormat.FULL);
try {
  inputDate = shortFormat.parse(inputString);
}
catch (ParseException pe) {}
try {
  inputDate = mediumFormat.parse(inputString);
}
catch (ParseException pe) {}
try {
  inputDate = longFormat.parse(inputString);
}
catch (ParseException pe) {}
try {
  inputDate = fullFormat.parse(inputString);
}
catch (ParseException pe) {}
if (inputDate == null) {
  System.out.println("Date could not be parsed");
}
else {
  System.out.println("You entered " + inputDate);
}

The try/catch code is a little messy, but it shows the general idea.