How to convert Java generics into kotlin language generics
The java code:
public abstract class Request<T, R extends Request> implements Serializable {}
But the kotlin code:How to do???
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"public abstract class Request<T, R extends Request> implements Serializable"，how to convert this use kotlin language?gooboot– gooboot2019-09-30 01:43:13 +00:00Commented Sep 30, 2019 at 1:43
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test this >>> something: StringElias Fazel– Elias Fazel2019-09-30 01:50:09 +00:00Commented Sep 30, 2019 at 1:50
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What's the question here? What have you done so far?Thingamajig– Thingamajig2019-09-30 02:56:38 +00:00Commented Sep 30, 2019 at 2:56
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3 Answers
According to my needs, I finally realized this way.
Open abstract class Request < T, out R > (url: String): Serializable where R: Request < T, R > {}
Open class GetRequest < T > (url: String): Request < T, GetRequest < T > (url){
}
Comments
You can just use the Java-to-Kotlin converter and get
abstract class <T, R : Request<*, *>> : Serializable
But the second Request (the one in extends Request) is a raw type which shouldn't be used in Java and is happily unsupported in Kotlin. Very likely it should be Request<T, R> instead; then the translation uses Request<T, R> in Kotlin too.
3 Comments
Cililing
"This type parameter violates Finite Bound Restriction."
Cililing
That's the error compiler throws when you try use two wildcards. Actually, I am not convenient that there should be
Request<T, R> - I see some use cases where second type parameter should be in Request bounds.
gooboot
Thank you very much for your help. According to my needs, I finally achieved this. Open abstract class Request < T, out R > (url: String): Serializable where R: Request < T, R > {} Open class GetRequest < T > (url: String): Request < T, GetRequest < T > (url){ }
public abstract class Request<T, R extends Request> implements Serializable {}
So, we have two generic types. T, which can by any type and R which have to extends Request. But, Request still requires two parameters.
In Java it's simpler as generics are not so strict and we can use raw type.
In Kotlin it would be like this:
abstract class Request<T, R : Request<*, *> : Serializable, but then we have a error: This type parameter violates Finite Bound Restriction. So, we need to specify somehow second type argument.
I am not sure if it is a correct way for your case, but you can do following:
abstract class Request<T, R : Request<*, R>> : Serializable {
abstract val dummy: R
}
class ExampleRequest<T, N> : Request<T, ExampleRequest<T, N>>() {
override val dummy: ExampleRequest<T, N> get() = this
}
1 Comment
gooboot
Thank you very much for your help. I learned some new knowledge from your help. According to my needs, I finally realized this way. Open abstract class Request < T, out R > (url: String): Serializable where R: Request < T, R > {} Open class GetRequest < T > (url: String): Request < T, GetRequest < T > (url){ }