Hi all, I have a java class with a method I want to override in my kotlin code. The method returns j...

# announcements

[Tobias G. Waaler]

Hi all,
I have a java class with a method I want to override in my kotlin code. The method returns java.lang.Object, meaning it can possibly be null, and I would like to return null from my kotlin implementation. The problem is that I am not allowed to specify the return type of my method as Any? when the method I'm overloading has return type Object 🤔

[diesieben07]

I just tried this out and it works fine in the way you described (specifying the return type as Any? in the override). Are you sure there are no @NonNull, etc annotations on the Java side?

[Tobias G. Waaler]

how strange. There's no @NonNull annotations

[Tobias G. Waaler]

I'm still on Kotlin 1.3.70, are you using 1.4?

[diesieben07]

yes, but that shouldn't matter. This behavior has existed since the very early days of Kotlin

[Tobias G. Waaler]

Return type of 'convert' is not a subtype of the return type of the overridden member 'public open fun convert(p0: ByteArray): Any defined in org.springframework.core.serializer.support.DeserializingConverter'

[Tobias G. Waaler]

I'll try to make a minimal reproduction

[Robert Jaros]

https://github.com/spring-projects/spring-framework/blob/master/spring-core/src/main/java/org/springframework/core/serializer/support/package-info.java

[Robert Jaros]

the @NonNull annotations are at the package level

[Tobias G. Waaler]

oh, I didn't know that

[Tobias G. Waaler]

https://github.com/spring-projects/spring-framework/blob/master/spring-core/src/main/java/org/springframework/core/convert/converter/Converter.java#L45

[Tobias G. Waaler]

the method I'm trying to override has an explicit @Nullable annotation, but I'm not sure how that interacts with the package level annotations

[Tobias G. Waaler]

But I'm inheriting from DeserializingConverter, and that method has no annotations, so it sort of makes sense

[Robert Jaros]

I would say, there is not much you can do about this if it doesn't compile 🙂

[Tobias G. Waaler]

seems it can be worked around by using delegation instead of inheritance

[Tobias G. Waaler]

in my case 🙂

[Tobias G. Waaler]

thank you both