I am newbie in kotlin, I trying to apply lesson on oop on

I don't know where's error in this code

open class Car( open val color:String?=null, open val brand:String?=null) {
    
    open fun speed(){
        println("max speed is 220")
    }
}

class Toyota() : Car() {
    override color = "White"
    override brand = "Toyota"
    
    override fun speed(){
        println("max speed is 360")
    }
}


fun main() {
   
    var car:Toyota = Toyota()
    car.speed()
    
   
}

CodePudding user response：

You are missing a val keyword in both parameters in Toyota class:

class Toyota() : Car() {
    override val color = "White"
    override val brand = "Toyota"

    override fun speed(){
        println("max speed is 360")
    }
}

Or you can do it even better by using Car constructor directly:

class Toyota : Car(color = "White", brand = "Toyota") {
    override fun speed(){
        println("max speed is 360")
    }
}

With this approach you can even make Car simpler (no need for open keyword on your properties):

open class Car(val color : String? = null, val brand : String? = null) {
    open fun speed(){
        println("max speed is 220")
    }
}

CodePudding user response：

You could override color and brand in the constructor of the subclass:

class Toyota(override val color: String = "White", override val brand: String = "White") : Car() {

  override fun speed() {
    println("max speed is 360")
  }

}