what does `expect` and `actual` translate to in java eg ```expect fun getPlatformName(): String``...

# getting-started

[Koneko Toujou]

what does expect and actual translate to in java

eg

expect fun getPlatformName(): String

actual fun getPlatformName(): String {
    return "Desktop"
}

[hfhbd]

https://kotlinlang.org/docs/multiplatform-connect-to-apis.html#rules-for-expected-and-actual-declarations
expect/actual are language keywords and not visible in the resulting target code.

[Koneko Toujou]

hmm ok

could i do the same thing in Java ?

[Koneko Toujou]

as i am unable to mix java and kotlin in the same module

[Landry Norris]

Java doesn’t have different platform targets, so I don’t believe there is an equivalent. It’s all JVM bytecode

[Koneko Toujou]

alright

[hfhbd]

expect/actual are used for Kotlin Multiplatform only to enable consuming a common declaration in your common code.

[Koneko Toujou]

🙂

[Landry Norris]

Why can’t you mix java and Kotlin in the same module?

[Goetz Markgraf]

The best analogy is interface and class but it is not a translation but only another implementation of a similar concept.

[Koneko Toujou]

it doesnt seem to compile the java code for some reason (class def not found)

[Landry Norris]

Have you set up the java plugin or added withJava to your jvm block in the kotlin block?

[Koneko Toujou]

i dont think so

[Landry Norris]

kotlin {
    jvm {
        withJava()
    }
}

Note you can’t have this and an android target in the same module.

[Koneko Toujou]

so for example, i cannot put it in this?

plugins {
    kotlin("multiplatform")
    id("org.jetbrains.compose")
    id("com.android.library")
}

kotlin {
    android()
    jvm("desktop") {
        jvmToolchain(11)
    }
    sourceSets {
        val commonMain by getting { dependencies { ... } }
        val androidMain by getting { dependencies { ... } }
        val desktopMain by getting { dependencies { ... } }
    }
}

android {
    namespace = "smallville7123.lua.jit.kotlin.common"
    compileSdkVersion(33)
    sourceSets["main"].manifest.srcFile("src/androidMain/AndroidManifest.xml")
    defaultConfig {
        minSdkVersion(24)
        targetSdkVersion(33)
    }
    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_1_8
        targetCompatibility = JavaVersion.VERSION_1_8
    }
}

[Landry Norris]

You can try, but the android plugin and the java plugin are incompatible. Why do you need Java code? IntelliJ can convert it to Kotlin.

[Koneko Toujou]

easier to write in java 🙂

[Koneko Toujou]

imma just have both a java module and a kotlin module

[Landry Norris]

You won’t be able to expect/actual like that. I’d create an interface, then implement it in each platform and pass in a factory or something.

[Koneko Toujou]

true, but i should be able to expect/actual via seperate kotlin + java modules

eg

kotlin-impl-bindings-desktop
java-impl-desktop

kotlin-impl-bindings-android
java-impl-android

however the :common module would require both desktop and android modules but i think it wont actually build both if only building for a single platform?

[Landry Norris]

You could have your Kotlin module depend on your java module, then expect/actual creating it. Since you’re doing a Kotlin module anyway, I’d highly recommend learning to write in Kotlin directly instead of doing the Java modules.

[Koneko Toujou]

alright