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Is it possible to add Android Java sources to a KMP project? If so, how? I'm sure this is a stupid question, but I've been unable to find a definitive answer in the usual places. The multiplatform documentation talks about how to add Java sources to the Jvm target here: <https://kotlinlang.org/docs/multiplatform-configure-compilations.html#use-java-sources-in-jvm-compilations> but this isn't interesting because I don't have a Jvm target, I have an Android target. Any ideas?

I would expect it to work the same way. Just create a `java` folder in the `androidMain` directory.

That isn't enough. The `java` folder isn't recognized as part of the source tree. The files don't get compiled. Also, just putting java source files in the `kotlin` folder in the source tree doesn't work either. They don't get compiled. I have a feeling that the Java compiler is only applied to the Jvm parts of the source tree, but I don't know why or how to change that behaviour.

I have this in my convention plugin.

```    private fun Project.configureMultiplatformAndroidSources() {
        (this.extensions.findByName("android") as? BaseExtension)!!.run {
            sourceSets["main"].manifest.srcFile("src/androidMain/AndroidManifest.xml")
            sourceSets["main"].res.srcDir("src/androidMain/res")
            sourceSets["test"].java.srcDir("src/jvmTestCommon/java")
            sourceSets["test"].java.srcDir("src/androidUnitTest/java")
        }
    }```
`sourceSets["test"].java.srcDir("src/androidUnitTest/java")` part let me do the `java` folder in the `androidUnitTest` so I thought it was just working.  So you need to just add `src/AndroidMain/java` to Android's main java source directories.

In a gradle.build.kts file it would be

```android {
    sourceSets["main"].java.srcDir("src/androidMain/java")
}```

Now Android Studio recognizes that folder as part of the source tree, and it compiles, but when I run a unit test I get a ClassDefNotFoundException on the Java class.

that's strange. If it compiles, I would expect it to find the class at runtime. Could be a bug in multiplatform android plugin where the runtime class path isn't including the output directory for java class. I know the tests find the java classes that I create in the test source set. I haven't played with adding java to the main source set.