getJarVersions.kt

fun getJarVersions(jarFolder: String): String {
    val jarFiles = File(jarFolder)
        .listFiles { _, name -> name.toLowerCase().endsWith(".jar") }
        ?: emptyArray()

    val text = jarFiles.map { "\t" + it }.sorted().joinToString("\n")
    return "${jarFiles.size} JAR files below ${jarFolder}: \n${text}"
}

object App {
    @JvmStatic
    fun main(args: Array<String>) {
        println(getJarVersions("lib"))
    }
}