@User shared a file: Untitled

@User uploaded a file: Abstract Java class to Kotlin interface help and commented: I am trying to convert an abstract Java class that some models extend to Kotlin. The classes that extend I would like to convert to data class in Kotlin, thus the abstract class would be an interface.

I am having trouble with the annotations in Kotlin. Getting this message:

This annotation is not applicable to target 'member property without backing field or delegate'

@User uploaded a file: Interface thus far

@fernandocortez you've successfully annotated fields in Java class, but there's no fields in given Kotlin interface.

@fernandocortez use

@JvmField

https://kotlinlang.org/docs/reference/java-to-kotlin-interop.html#instance-fields

but i guess you won't be able to put a field into an interface

@JvmField won't help.

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@miha-x64 @Andreas Sinz ok thanks for the help. What looks like is going to work is to move the annotations to the data class implementing the interface. It'll lead to duplication of the annotations in the data classes, but what I really want is not to have to maintain that

toString

function

Does anyone here know how to retrieve KClass of a class in java code?

Try

JvmClassMappingKt.getKotlinClass(javaClass)

.

appears to be

JvmClassMappingKt.getKotlinClass(clazz)

Thanks. 👍

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what is the best way to process a list and produce a new list with potentially fewer elements? I know I could do

listOf(1,2,3).mapNotNull { if (it %2 != 0) "hi ${it}" else null }

but (a) that relies on

null

never being a valid result element and (b) does not work for

flatMap

. Perhaps I should just use a classical for loop and add to the result list?

or perhaps first filter and then map?

What’s wrong with

filter

?

that I have to evaluate the same expression twice (and code it twice). concrete example: I want to create objects from files in subdirs of a given path, but only if the subdir name is from a "valid" list. in the

map

i have a

when(subdirname) { "foo" -> createFoo(subdirname); "bar" -> createBar(subdirname)

. any subdirs not "foo" or "bar" I want to ignore. So I would first have to filter on the names, and then still have the "when" in the map repeating the list of valid names

thus I end up writing

filter { it.name in listOf("foo", "bar") }.map { when(it.name) { "foo" -> ...; "bar"->...; }

@nkiesel what about calling

map

directly and filter all the rest out with

else

?

filter out how exactly? AFAIK, map returns a new list with a 1:1 mapping from elements of the original one. Thus, the best I can come up with is to use "UNWANTED" (e.g. null) as placeholder and then filter the resulting list

@nkiesel this way

map { when(it.name) { "foo" -> ...; "bar"->...;  else { /** this is your "filter" */} }

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i don't think that works for him, if he wants to filter, as he said map needs a return value

What does

as

do when used as a statement?

override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other?.javaClass != javaClass) return false

        other as EntityNotFoundException

        if (entityId != other.entityId) return false
        if (entityType != other.entityType) return false

        return true
    }

This was generated by IDEA

@dstarcev it's a cast

same that

((EntityNotFoundException) other)

would do in Java