no-ocp.kt

enum class Shipping {
    JNE, JNT
}

class Product() {
    fun calculateShippingPrice(price: Int, shipping: Shipping): Int{
        return when(shipping){
            Shipping.JNE -> 12 * price
            Shipping.JNT -> 20 * price
            else -> 0
        }
    }
}

fun main() {
    val product = Product()
    val price = product.calculateShippingPrice(10_000, Shipping.JNE)
    println(price)
}

ocp.kt

abstract class Shipping {
    abstract fun calculateShippingPrice(price: Int): Int
}

class JNE: Shipping() {
    override fun calculateShippingPrice(price: Int): Int {
        return 12 * price
    }
}

class JNT: Shipping() {
    override fun calculateShippingPrice(price: Int): Int {
        return 20 * price
    }
}

class Product() {
    fun calculateShippingPrice(price: Int, shipping: Shipping): Int{
        return shipping.calculateShippingPrice(price)
    }
}

fun main() {
    val product = Product()
    val price = product.calculateShippingPrice(10_000, JNE())
    println(price)
}