How to initialize a variable of an abstract class from a child class - kotlin

Question

I have an abstract class:
inner abstract class Base {
fun Buscar(): Int {
// Do something with a object called Q
}
}
And two secondary class that I need to initialize Q with certain class
inner class BFS(): Base() {
constructor(): this() {
Q = Cola()
}
}
inner class DFS(): Base() {
constructor(): this() {
Q = Pila()
}
}
How can I do that?
--- EDIT ---
Pila() and Cola() are classes from an abstract class called Secuencia:
abstract class Secuencia<T> { ... }
public class Pila<T> : Secuencia<T>() { ... }
public class Cola<T> : Secuencia<T>() { ... }

Answer 1

You just need to make Q abstract and initialise it in your class, e.g.
sealed class Algo(val message: String)
class Cola : Algo("cola")
class Pila : Algo("pila")
abstract class Base {
// all concrete classes need to define a value for 'q'
abstract val q: Algo
fun buscar(): Int {
// you can reference q here since a concrete class will have initialised it
println(q.message)
return 1
}
}
class BFS(): Base() {
// since q is abstract it needs to be overridden in a concrete class
override val q = Cola()
}
class DFS(): Base() {
override val q = Pila()
}
fun main() {
BFS().buscar()
DFS().buscar()
}
>> cola
>> pila