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Java Forum / General / April 2006Date: Can you have one that is just mm/dd or mm/yyyy etc?
I need to store some data in this format: "mm/yyyy" as a Date or DateTime. I can create SimpleDateFormat("mm/yyyy"), but when I do format.parse() on "12/2001" it helpfully returns "December 1, 2001". I need to store it as a DateTime of December 2001. Storing it as a String is not an option. Has anyone dealt with this kind of situation before and could point me in the right direction to understand how to handle this? Thanks, Libby >I need to store some data in this format: "mm/yyyy" as a Date or > DateTime. I can create SimpleDateFormat("mm/yyyy"), but when I do > format.parse() on "12/2001" it helpfully returns "December 1, 2001". I > need to store it as a DateTime of December 2001. Storing it as a String > is not an option. Why is storing the date as a String not an option? I think you'll need to go that route. Or you could put the month name in a String and the year in an int and then bundle them together in a new Class with a name like MonthYear; that class could have methods to get the year and the month individually for convenience and to format the value however you want it. Another way to go would be store an arbitrary day with your month and year and then just ignore the day portion but I don't much like that; it feels like bad design to me although I can't articulate exactly what is wrong with it. > Has anyone dealt with this kind of situation before and could point me > in the right direction to understand how to handle this? This is a pretty unusual requirement, at least in my experience. In my view, a date always includes a year, month and a day of the month; I wouldn't even call the combination of year and month alone a date, really. In business, you normally store a year, month and a day for every 'event', like a bill payment or an insurance claim. Your reports may end up summarizing by year and month but then the month/year combination would normally be stored as a String, if it was stored at all. At least that's been my experience. Sorry I couldn't tell you what you wanted to her. Maybe someone else will have a different take on this question. -- Rhino >Has anyone dealt with this kind of situation before and could point me >in the right direction to understand how to handle this? You can store the date as a long millis since 1970 or int days since 1970 and use Date, GregorianCalendar and SimpleDateFormat when you need to display it.  SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > I need to store some data in this format: "mm/yyyy" as a Date or > DateTime. No, you don't. You need to display them as mm/yyyy. Store the date in milliseconds since the epoch, and use a display format which suppresses the day when you display the value. /Thomas SignatureThe comp.lang.java.gui FAQ: ftp://ftp.cs.uu.nl/pub/NEWS.ANSWERS/computer-lang/java/gui/faq http://www.uni-giessen.de/faq/archiv/computer-lang.java.gui.faq/ Unfortunately, yes, I do. At some point the stored date will be embedded in SQL and, if it is mm/yyyy format the SQL will be "LIKE %theMm/yyyyDate%", and if it is mm/dd/yyyy format the SQL will be "=theMm/dd/yyyyDate". I will need to evaluate the stored "Date" to determine if a day exists in it, and build the SQL accordingly. Storing the Date as a String would of course be the way to handle this, except that the Date Object is already previously used in this application I am patching. I don't wanna rewrite the whole thing... > Unfortunately, yes, I do. No, you don't. You are mixing up the representation of a value, and the value itself. But since this is getting boring. May I suggest that you at least think about the above sentence for, hmm, lets say 10 seconds, and study the API documentation of SimpleDateFormat? /Thomas SignatureThe comp.lang.java.gui FAQ: ftp://ftp.cs.uu.nl/pub/NEWS.ANSWERS/computer-lang/java/gui/faq http://www.uni-giessen.de/faq/archiv/computer-lang.java.gui.faq/ OK, you're right I don't. I studied the API doc for SimpleDateFormat before submitting my plea for help. I guess my real question is, how do I know if a Date portion such as day is not a valid value for my application, ie when Date = 01/05/2001, how do I know to ignore the month portion (or day, or year) because it is only a placeholder? If I try to create a Date with 01/00/2001 or some such, I of course get an unparseableDate exception. I apologize for boring you, I am not nearly as smart as most readers of this forum, which is why I came to it for help when I couldn't find a way in the API. Hopefully I will come away from here smarter after partaking of the comp.lang.java.programmer fountain of knowlege. "LibbyChantel" wrote... > "Thomas Weidenfeller" wrote... >> "LibbyChantel" wrote... > Unfortunately, yes, I do. >> No, you don't. You are mixing up the representation of a value, >> and the value itself. > OK, you're right I don't. > [quoted text clipped - 6 lines] > with 01/00/2001 or some such, I of course get an > unparseableDate exception. I think you still need to think over what Thomas said; to realize that there's a difference between a value and its representation. A Date is internally represented by a long (number of milliseconds since since January 1, 1970, 00:00:00 GMT), but as such it can only have values that corresponds to valid times and dates. There's no way around that. You actually provided half the answer to the solution yourself in a previous post. You want to format an SQL statement (which is represented by a *String*): "LIKE %theMm/yyyyDate%" ...which means that what you put into that string should be a string itself. In order to provide the *format* of that part of the string, you simply use a SimpleDateFormat to format a valid Date into the String representation you like, even excluding the day part. That is what you want to put into your SQL statement, not the Date itself. // Bjorn A You guys are totally missing the point. My question is not how to format a date to use it in SQL, which is why I left that information out originally. My question was, is there a way to save only a portion of a date in a Date object? My solution is to extend the Date Object and add a field to it which denotes whether the entire date is valid, or just some combination of mm/yyyy, etc. But I thought maybe there was a way to use the original Date object without "enhancing" it. I am REQUIRED to store the date in a Date, even if it is invalid : ) Thanks, Libby > You guys are totally missing the point. My question is not how to > format a date to use it in SQL, which is why I left that information [quoted text clipped - 6 lines] > Date object without "enhancing" it. I am REQUIRED to store the date in > a Date, even if it is invalid : ) Last time I did that sort of thing was in a system that needed to deal with ordinary dates, financial periods and birth/death dates of composers and dates of compositions, which are not always known closer than a year, a decade or even a century. I held two fields: Format code Date value The format code was set by parsing the input date value and was used to format output so the output looked the same as the input. It could also be used for validation if only certain date formats were permitted in some date fields. The date value was held internally as 8 digits ordered as ccyymmdd so any format of date could be compared with any other and arbitrary collections of dates could be sorted. If the input and display format didn't include a month and/or day the relevant parts of the internal value were set to appropriate values that corresponded to valid dates. Some of the types of date that the system were required to accept were: Format Example Internal form calendar date 26/04/05 20050426 a month May 1999 19990501 financial qtr 3rd q 2001 20010701 a year 1492 14920101 a century 19th 18000101 BC year 55BC -00550101 It must have worked OK: the system was in use for 20 years until it was rewritten to migrate it from ICL 2900 hardware to a UNIX RDBMS system, having slid through the change of century with no problems at all. With the possible exception of BC dates you could do the same but handle the internal date value as a Date class or an SQL date. HTH Signaturemartin@ | Martin Gregorie gregorie. | Essex, UK org | "LibbyChantel" wrote... > You guys are totally missing the point. Well, you just didn't express your point very clear. ;-) We *did* answer your question, but maybe we would have phrased the answers a bit differently if you had stated your point in another way. > My question was, > is there a way to save only a portion > of a date in a Date object? As we've said, the date object *always* has a long which represents a valid date, there's no way around that. > My solution is to extend the Date Object and add a field > to it which denotes whether the entire date is valid, or > just some combination of mm/yyyy, etc. But I thought maybe > there was a way to use the original Date object without > "enhancing" it. I am REQUIRED to store the date in > a Date, even if it is invalid : ) I'm not sure I dare to ask you why? ;-) What would the difference be, towards a solution where you combine arbitrary Date objects with specialized SimpleDateFormats? Maybe if you could tell us more what those dates are supposed to *do*? On another note, similar things has been done, even within the library. e.g. java.sql.Date and java.sql.Time are subclasses of java.util.Date, where the time respectively the date part is "hidden". So if it *really* is required to store invalid dates, that's one way to go, though it seems almost simpler to just create a completely new class, as it tends to be pretty ugly to break the Liskov substitution principle... Not knowing what you actually need it for, I would rather suggest using Composition instead of Inheritance, in order to only expose the necessary features. // Bjorn A > You guys are totally missing the point. I'm not totally following either. > My question is not how to > format a date to use it in SQL, which is why I left that information > out originally. My question was, is there a way to save only a portion > of a date in a Date object? No, there isn't. > My solution is to extend the Date Object and add a field to it which > denotes whether the entire date is valid, or just some combination of > mm/yyyy, etc But I thought maybe there was a way to use the original > Date object without "enhancing" it. I am REQUIRED to store the date in > a Date, even if it is invalid : ) Careful the way you phrase this. You say you're "required to store the date in a Date", but might your requirements be "store the date", without regards of the actual class where the Date is stored? If you really do need to use the Date object, you're out of luck. The date object simply doesn't support what you want. Even if you extend the Date object to add functionalities, when you pass that Date object to an SQL database, the database isn't going to know about your extended functionalities, and will simply store Dates the way it always has. You should probably go a level higher in abstraction, and describe what you're trying to do, rather than describe how you want to do it. - Oliver > My question was, is there a way to save only a portion >> of a date in a Date object? > > No, there isn't. You can use a convention, e.g. story YYYY-MM as if it were YYYY-MM-01. SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > You can use a convention, e.g. story YYYY-MM as if it were YYYY-MM-01. At first I thought both Roedy and Thomas were oh so wrong, but I realize that they read the original quote: >some data in this format: "mm/yyyy" Meaning that the OP has a column of date all of which only has month resolution. If so, they are right, just display it with less resolution might be your ticket. If "some" applied to some of the rows in one column then Libby is SOL, because 01/01/2006 00:00:00.00 stored in either a java.util.Date or a DB DATETIME needs something else to tell us if it is exactly that time or trying to represent the whole month of January or even the whole year. Others talked about an additional column which sort of implied that they were thinking of there was mixed resolutions in one DATETIME column. Libby, here are some things to consider: >but when I do format.parse() on "12/2001" it helpfully returns >December 1, 2001". No, it returns a java.util.Date which when you call the toString() either explicitly or when you are using System.out.print(myDate), shows a millisecond value converted to localized String. Go back to this code and consider always showing it to yourself while debugging and to the user using a SimpleDateFormat as several others have pointed out. If this consistency of simply ignoring the smaller fields works your in business. One thing to watch is to NOT take my suggestion and print out everything in the Date wherever you have it in application (particularly right before displaying to the user and right before shipping to the DB) and make sure 2005-04-01 T 00:00:00.0000 (using ISO 8601 notation to avoid any month day confusion in this discussion), doesn't magically drift to 2005-01-04 T 15:34:17.1234 because you ran the application in the afternoon and somehow you transfered the right date over the present date time (just past 3:30 in the afternoon). Meanwhile, your suggested use of SQL where you "I will need to evaluate the stored "Date" to determine if a day exists in it, and build the SQL accordingly. " seem suspiciously unsual to me. I don't get how the word "the" is imbedded in a real DATETIME as %theMm/yyyyDate%" and how you can use the % operator on it. In fact, I'd be interested in knowing what DB you are using and what SQL you can use. I dont' thing you want to have the DB think in terms of Strings, but use SQL Date creating expressions to specify the appropriate midnight-fixed DATETIME. Particularly watch for comparing to not right NOW, but today at midnight with consideration for when you want this mornings midnight or tonights. Good luck, and don't be discouraged by people answering the wrong question. Hopefully, I have answered the right question. If not do let me know. -Paul On Thu, 27 Apr 2006 22:01:09 -0700, "P.Hill" <goodhillREMOVE@xmissionREMOVE.com> wrote, quoted or indirectly quoted someone who said : > >some data in this format: "mm/yyyy" another way to store it is as binary int of the form yyyymm you use %100 or /100 to get the fields. In that form you can still compare date order and equality. SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. 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