Any idea what's happening here? `lastJobExecution`...

# getting-started

[df]

Any idea what's happening here? lastJobExecution is clearly of type JobExecution?

[Michael Krussel]

What's the declaration of getLastJobExecution?

Does this compile using gradle, sometimes the IDE reports false positive errors.

[df]

@Nullable
	JobExecution getLastJobExecution(String jobName, JobParameters jobParameters);

And the maven build fails with the same error

[Michael Krussel]

What is BatchStatus.FAILED? Is that a mutable boolean variable or is it being compared to something under the tooltip?

[Michael Krussel]

This compiles for me

class JobExecution(
    val isSomethingICannotSee: Boolean
)
typealias JobParameters = String
const val IMPORT_ORDER_JOB_NAME = "name"
interface JobRepository {
    fun getLastJobExecution(jobName: String, jobParameters: JobParameters): JobExecution?
}

lateinit var jobRepository: JobRepository
fun validate(jobParameters: JobParameters) {
    val lastJobExecution: JobExecution? = jobRepository.getLastJobExecution(
        IMPORT_ORDER_JOB_NAME,
        jobParameters
    )

    val error = when {
        lastJobExecution == null -> "Job does not exist"
        lastJobExecution.isSomethingICannotSee -> "other error"
        else -> null
    }
}

[Michael Krussel]

Could be some Java/Kotlin interop issue. but the null check should be valid.

[Jacob]

Had the same issue years ago. Never figured it out

[Jacob]

https://stackoverflow.com/questions/56653315/why-is-kotlin-double-equals-not-finding-a-equals-method

[df]

Thanks for sharing Jacob. I gave up after a couple of minutes and went with lastJobExecution?.someProperty == null which worked fine.

[Michael Krussel]

I would report a bug to Kotlin.

[Klitos Kyriacou]

You could also try lastJobExecution === null - which seems unnecessarily longer than == but still shorter than your last workaround.

[Jacob]

I suspect it's springs fault. https://github.com/spring-projects/spring-batch/blob/main/spring-batch-core/src/main/java/org/springframework/batch/core/package-info.java makes all parameters nonnullable by default which is preventing the equals implementation from being picked up by kotlin

[Jacob]

They need to add @Nullable to here https://github.com/spring-projects/spring-batch/blob/42b1464a0994460112c854c4f93903f59c2a9bc9/spring-batch-core/src/main/java/org/springframework/batch/core/ExitStatus.java#L201

[Klitos Kyriacou]

That's interesting, but if Spring Batch inadvertently defines equals(Any) instead of equals(Any?), wouldn't ExitStatus still inherit equals(Any?) from its superclass Any?

[Michael Krussel]

Not really, since even though null is part of the type system it doesn't change the function signatures on the JVM. So the function is overriding the function but not in a valid way since they are restricting the type of an input parameter. Kotlin probably wouldn't allow it, but since null is not part of the Java type system, Java cannot. So yes, Spring should annotate the override with Nullable, since they handle null and not handling null would be a contract violation. So Kotlin, knows if they call equals they will get the one in ExitStatus, and not the one in Any , but Spring says they cannot pass null into it, so the compiler is stuck saying the operation is illegal.