Hey, I have this Converter in Kotlin: ```class ExampleConverter<T> : Converter<T, String&g...

# announcements

[Björn Mayer]

Hey,
I have this Converter in Kotlin:

class ExampleConverter<T> : Converter<T, String> {
    override fun convert(source: T): String? {
        TODO("Not yet implemented")
    }
}

it implements this Java interface:

@FunctionalInterface
public interface Converter<S, T> {

	/**
	 * Convert the source object of type {@code S} to target type {@code T}.
	 * @param source the source object to convert, which must be an instance of {@code S} (never {@code null})
	 * @return the converted object, which must be an instance of {@code T} (potentially {@code null})
	 * @throws IllegalArgumentException if the source cannot be converted to the desired target type
	 */
	@Nullable
	T convert(S source);

}

The IDE says, that everything is fine.

However when I try to compile I get:

Class 'ExampleConverter' is not abstract and does not implement abstract member public abstract fun convert(p0: T!!): String?
'convert' overrides nothing

Any idea?

[Pavel Sidyakin]

Try
override fun convert(source: T*?*): String?

[Björn Mayer]

Still doesn’t compile.
And the IDE is now also complaining:

[Pavel Sidyakin]

Strange. I can't reproduce the issue.
Possibly your module has some issues with java or kotlin version.
Try to add this in build.gradle of your module:

android {
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
}

[Björn Mayer]

My kotlinOptions look like this:

kotlinOptions {
                freeCompilerArgs = listOf(
                    "-progressive",
                    "-Xinline-classes",
                    "-Xjsr305=strict",
                    "-Xjvm-default=enable",
                    "-Xopt-in=kotlin.ExperimentalUnsignedTypes"
                )
                jvmTarget = "11"
                javaParameters = true
            }

Java Toolchain is set to 11:

java {
    toolchain {
        languageVersion.set(JavaLanguageVersion.of(11))
    }
}

[Pavel Sidyakin]

Looks like this is the problem:

"-Xjsr305=strict",

[Pavel Sidyakin]

https://kotlinlang.org/docs/java-interop.html#jsr-305-support

[Pavel Sidyakin]

Try to remove it or set to "warn"

[Pavel Sidyakin]

And BTW, why should you use the java interface? Can you just create the same interface in Kotlin? It's very simple interface.

[Björn Mayer]

the interface comes from Spring

[Pavel Sidyakin]

I see, ok

[J.Snow]

look like your are using

org.springframework.core.convert.Converter

which is come from spring

[Björn Mayer]

The thing with JSR 305 is: It is kinda a default. This compiler Arg is present in every new IDE project.
I wonder why this should cause such problems now.

I also tried to remove the other compilerArgs.
The project does compile without progressive

[Björn Mayer]

It fails to compile with Kotlin 1.4.20. Kotlin 1.4.10 works
https://github.com/bjoernmayer/progressive-kotlin-issue

[Björn Mayer]

removing progressive or Xjsr305=strict compiler args leads to succesful compilation.
However: both shouldn’t cause this IMO

[Björn Mayer]

I opened an issue 🤞
https://youtrack.jetbrains.com/issue/KT-46076