How should I make this Spring formatter implementation suppo

Question

How should I make this Spring formatter implementation support LocalDate nullable ``` fun localDateFormatter Formatter lt LocalDate gt return object Formatter lt LocalDate gt override fun parse text String locale Locale LocalDate return LocalDate parse text DateTimeFormatter ISO DATE override fun print obj LocalDate locale Locale String return DateTimeFormatter ISO DATE format obj ```

Jukka Siivonen · Answer

I can t make parse return LocalDate no matter what

Jukka Siivonen · Answer

If I put ```override fun parse text String locale Locale LocalDate ``` it gives me error Return type is LocalDate which is not a subtype of overridden

Nikky · Answer

LocalDate is a subtype of LocalDate

Nikky · Answer

so you need to make the type it formats nullable or handle nullability ``` defaultDate ```

Nikky · Answer

or throw a exception

Jukka Siivonen · Answer

Using

Jukka Siivonen · Answer

```override fun parse text String locale Locale LocalDate ``` does not compile

Jukka Siivonen · Answer

whatever the implementation is

Jukka Siivonen · Answer

because changing return type LocalDate gt LocalDate then gives compiler error ```Return type is LocalDate which is not a subtype of overridden```

Nikky · Answer

because its for `Formatter lt LocalDate gt ` with that signature you would need `Formatter lt LocalDate gt `

Jukka Siivonen · Answer

same problem

Nikky · Answer

thats why you should isntead handle null on the parser call

Nikky · Answer

LocalData parse returns LocalDate because the input could be junk

Jukka Siivonen · Answer

I don t understand

Nikky · Answer

so adding elvis operator to get a default or to throw would fix that

Jukka Siivonen · Answer

because the problem is not the actual implementation but defining the nullable type

Nikky · Answer

to me it seems like the actual problem is that the return type is non nullable but your function return null maybe i am confused because i do not have the code in a IDE

Jukka Siivonen · Answer

``` Bean fun localDateFormatter Formatter lt LocalDate gt return object Formatter lt LocalDate gt override fun parse text String locale Locale LocalDate return null override fun print obj LocalDate locale Locale String return DateTimeFormatter ISO DATE format obj ```

Jukka Siivonen · Answer

does not compile

Jukka Siivonen · Answer

Return type is LocalDate which is not a subtype of overridden

Nikky · Answer

because the generic argument is LocalDate and not LocalDate

Jukka Siivonen · Answer

fixed same problem

Nikky · Answer

it could also be that formatter only takes T Any and nullability was not considered

Nikky · Answer

now the print function should take a nullable though

Jukka Siivonen · Answer

Formatter is Java

Jukka Siivonen · Answer

```public interface Formatter lt T gt extends Printer lt T gt Parser lt T gt ```

Jukka Siivonen · Answer

``` FunctionalInterface public interface Printer lt T gt Print the object of type T for display param object the instance to print param locale the current user locale return the printed text string String print T object Locale locale ```

Jukka Siivonen · Answer

``` FunctionalInterface public interface Parser lt T gt Parse a text String to produce a T param text the text string param locale the current user locale return an instance of T throws ParseException when a parse exception occurs in a java text parsing library throws IllegalArgumentException when a parse exception occurs T parse String text Locale locale throws ParseException ```

Nikky · Answer

it looks like it should work yeah

Jukka Siivonen · Answer

changing print LocalDate give me print overrides nothing

Nikky · Answer

seems broken do you want nullable Datetime though

Nikky · Answer

i d just hadle it in the parser and throw exception when something is invalid