How to initialize an empty ArrayList in Kotlin?

Question

I have an empty arraylist:

var mylist: ArrayList<Int> = ArrayList()

When I want to set value in it I got this error:

java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0

The question is: How can I initialize my list?

Don't use `set` but `add.`. Also use the factory instead of constructor: `val list = mutableListOf()`. Also note I specified `val` instead of `var` (it has nothing to do with the list's mutability). — Marko Topolnik, Jun 12 '18 at 10:41

LuCio · Accepted Answer · 2018-06-12T11:02:44.083

128

According to the api-doc:

val list = arrayListOf<Int>()

edited Jun 12 '18 at 11:02

answered Jun 12 '18 at 10:44

LuCio

1

Isn't an arrayList different from an array in kotlin? – SMBiggs Mar 28 '20 at 06:05
@SMBiggs See SO [Q&A](https://stackoverflow.com/questions/76051010/what-is-the-difference-between-array-list-and-arraylist-in-kotlin) – LuCio Aug 18 '23 at 08:32

score 44 · Answer 2 · answered Jun 12 '18 at 10:44

44

I suggest you write

var myList: ArrayList<Int> = arrayListOf()

answered Jun 12 '18 at 10:44

Szymon Chaber

15

`val myList = arrayListOf()` reads much better. – Marko Topolnik Jun 12 '18 at 11:06
What if it's an array, not an arrayList? – SMBiggs Mar 28 '20 at 06:05
you can do this with ```val value= Array(20) { 0 }``` – sajadab Jan 26 '22 at 12:41

2 Answers2