OOP in Kotlin

oop_kotlin.kt

/**
 * You can edit, run, and share this code.
 * play.kotlinlang.org
 */
fun main() {
    val myCar = Car()
    println(myCar.color)
    println(myCar.model)
    myCar.drive()
    
    val myFunnyCar = FunnyCar(
        color = "Green"
        //model = "GLE"
    )
    
    println(myFunnyCar.color)
    println(myFunnyCar.model)
    
    val myTruck = Truck(
    	color = "Magenta",
        model = "AMG"
    )
    myTruck.speed(100, 199)
    println(myTruck.color)
    println(myTruck.model)
    myTruck.drive()
    
    val btn = CustomButton(label = "Submit")
    btn.onClick(message = "clicking...")
    
    // extension functions
    println("Hello".bolaji(", World"))
    println("Hello".removeFirstAndLastChars())
    
    val person = Person(
    	name = "Joe",
        lastName = "Ball",
        age = 23
    )
    println(person)
}

data class Person(
	val name: String,
    val lastName: String,
    val age: Int
)

// This extends the base string class to include
// custom functions beyond what the kotlin language 
// gives us
fun String.bolaji(toAppend: String): String {
    return this.plus(toAppend)
}

fun String.removeFirstAndLastChars(): String = this.substring(1, this.length - 1)

interface Clickable {
    fun onClick(message: String)
}

class CustomButton(val label: String): Clickable {
    override fun onClick(message: String) {
        println("button with label '$label' was clicked with message '$message'")
    }
}

class Car {
    // immutable
    val color: String = "Red"
    val model: String = "XMD"
    
    // mutable
    var isDriving: Boolean = false
    
    fun drive() {
        this.isDriving = true
        println("Driving .... vrooom!")
    }
}

// inheritance
// class Truck(color: String, model: String): FunnyCar(color, model)

class Truck(color: String, model: String): FunnyCar(color, model) {
    override fun drive() {
        println("a truck is being driven")
    }
}

// class must be open in order to inherit it
open class FunnyCar(
	val color: String = "Blue",
    val model: String = "xmdle"
) {
    init {
        if (color == "Green") {
            println("Yayy Green")
        } else {
            println("$color is not green")
        }
    }
    
    fun speed(minSpeed: Int, maxSpeed: Int) {
        println("min speed: $minSpeed\nmax speed: $maxSpeed")
    }
    
    open fun drive() {
        println("car is being driven")
    }
}