DIP.kt

interface Database {
    fun read(): String
    fun create(): String
}

class MySQL: Database {
    override fun read() = "MYSQL read database"
    override fun create() = "MYSQL create database"
}

class MongoDB: Database {
    override fun read() = "MongoDB read database"
    override fun create() = "MongoDB create database"
}

class Controller(private val database: Database) {
    fun createData() = database.create()
    fun readData() = database.read()
}

fun main() {
    val controller = Controller(MySQL())
    val result = controller.readData()
    
    println(result)
}

no-DIP.kt

class Database {
    fun create() = "create database"
    
    fun read() = "read database"
}

class Controller {
    private val database = Database()
    
    fun createData() = database.create()
    
    fun readData() = database.read()
   
}

fun main() {
    val controller = Controller()
    val result = controller.readData()
    
    println(result)
}