Date Formatting to yyyymmdd in a TXT file

Question

Converting User Input Date Format from dd/mm/yyyy to yyyymmdd to facilitate date checking. The code writes the date to a .TXT file but write it to it in the dd/mm/yyyy format when I'm wanting it in yyyymmdd. The method ValidDate is what I've tried to fix the problem so far but still isnt working. All help appreciated.

Possible duplicate of [Is Java "pass-by-reference" or "pass-by-value"?](https://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value) — PM 77-1, Jul 31 '19 at 17:08
Please try to format your code for increased readability including proper indentation, removing extra empty lines and removing irrelevant comments. — Joakim Danielson, Jul 31 '19 at 17:11
FYI, the terribly troublesome date-time classes such as [`java.util.Date`](https://docs.oracle.com/javase/10/docs/api/java/util/Date.html), [`java.util.Calendar`](https://docs.oracle.com/javase/10/docs/api/java/util/Calendar.html), and `java.text.SimpleDateFormat` are now [legacy](https://en.wikipedia.org/wiki/Legacy_system), supplanted by the [*java.time*](https://docs.oracle.com/javase/10/docs/api/java/time/package-summary.html) classes built into Java 8 and later. See [*Tutorial* by Oracle](https://docs.oracle.com/javase/tutorial/datetime/TOC.html). — Basil Bourque, Jul 31 '19 at 17:27

score 1 · Answer 1 · answered Jul 31 '19 at 17:23

1

You need to execute the parse to have a new date from string. Try change your validDate and execute a parse, like this:

    SimpleDateFormat df = new SimpleDateFormat("dd/MM/yyyy");
    Date theDate = df.parse(date);
    SimpleDateFormat formater = new SimpleDateFormat ("yyyymmdd");
    String formatedDateAsString = formater.format(theDate);

answered Jul 31 '19 at 17:23

Mychell Teixeira

80
4

Thanks for replying. Where exactly would I place this code you have given me? just replace what I have in the ValidDate method with this? Sorry quite new to java. Thanks again. – sr864 Jul 31 '19 at 17:36
@sr864 to your validateDate function. – Apoorva sahay Jul 31 '19 at 17:58
You should create a new method, String dateConverter(String date), for example. Then on dateConverter method you make: SimpleDateFormat df = new SimpleDateFormat("dd/MM/yyyy"); Date theDate = df.parse(date); SimpleDateFormat formatdate = new SimpleDateFormat ("yyyymmdd"); return formatdate.format(theDate); After, you can use this method to write on file: pw.println(dateConverter(formatdate)+","+litres+","+cost); – Mychell Teixeira Jul 31 '19 at 18:04
That all works apart from the last line when I amend the pw.println to that netbeans doesn't allow it and it says "Void type not allowed here" and gives me the option to Flip Operands. Am I doing something wrong? Thanks again – sr864 Jul 31 '19 at 19:06
dateConverter(..) should returns the formatted string. – Mychell Teixeira Jul 31 '19 at 19:15
Still seems to not be working the only error that shows up is for the printwriter line – sr864 Jul 31 '19 at 22:09
I've edited the original code at the top to what I have now – sr864 Jul 31 '19 at 22:13
Buddy, try do not use variable with initial letter on uppercase. Maybe your IDE is confusing. – Mychell Teixeira Aug 01 '19 at 14:54

Basil Bourque · Answer 2 · 2019-07-31T17:27:15.600

tl;dr

LocalDate
.parse(
    "23/01/2001" , 
    DateTimeFormatter.ofPattern( "dd/MM/uuuu" )
)
.format(
    DateTimeFormatter.BASIC_ISO_DATE 
)

See this code run live at IdeOne.com.

20010123

Tip: Better to exchange date-time data textually using only the standard ISO 8601 formats.

java.time

You are using terrible date-time classes that were supplanted years ago by the modern java.time classes as of the adoption of JSR 310.

`LocalDate`

The LocalDate class represents a date-only value without time-of-day and without time zone or offset-from-UTC.

ISO 8601

Your desired output format is known as the "Basic" variation of the standard ISO 8601 formats. I suggest considering using the expanded variation, YYYY-MM-DD, as it is more recognizable and readable.

Also, the expanded variations are used by default in the java.time classes when parsing/generating strings. So no need to specify a formatting pattern.

LocalDate ld = LocalDate.parse( "2019-01-23" ) ;  // Parsed by default, no need to specify a formatting pattern.

Date Formatting to yyyymmdd in a TXT file

2 Answers2

tl;dr

java.time

LocalDate

ISO 8601

`LocalDate`