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Android Kotlin for Java Developers Modelling Solitaire Building the Foundation

Sai Krishna Katkam
PLUS
Sai Krishna Katkam
Courses Plus Student 1,946 Points
Posted by Sai Krishna Katkam
Sai Krishna Katkam
Courses Plus Student 1,946 Points

How can we use "val" keyword with MutableList in Kotlin?! Isn't it supposed to stop us from changing a value?

In the Solitaire app, Ben declares a property using val. I wonder how can a mutable object be declared as val?

FoundationPile.kt 
class FoundationPile(val suit: String) {

val cards: MutableList<Card> = mutableListOf()

   fun reset() 
  { 
   cards.clear()
   }
}

1 Answer

Ben Deitch
STAFF
Ben Deitch
Treehouse Teacher
Ben Deitch
Ben Deitch
Treehouse Teacher

That's actually not a mutable object. You can modify the contents of the list (even clearing it), but you're not actually changing the list itself; it's the same list just with different contents.

So while you can use the 'clear' method to reset the cards list, you couldn't set it equal to a new list.

val cards = mutableListOf()
cards.clear() // Ok
cards = mutableListOf() // Not ok