Public Modifier usage

marketing_person.kt

fun main() {
    val recipient = User()
    recipient.chat(
        "Hello, ${recipient.displayName} Greetings for the day! Black Friday Sale is nearing"
    )
    
    // marketing person can only send promotion messages to the user.
    // users confendential information such username, password are not visible outside the class.
}

User.kt

class User {

    private var userName: String? = null // not accessible outside the class
    private var password: String? = null // not accessible outside the class

    val displayName: String = "Joey" // accessible outside the class

    private val messages = mutableListOf<String>()

    private fun resetPassword() {

    }

    fun chat(message: String) {
        messages.add(message)
    }

}