How to initialize an empty ArrayList in Kotlin? [duplicate]

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<Int>(). Also note I specified val instead of var (it has nothing to do with the list's mutability). — Marko Topolnik
– Marko Topolnik, Commented Jun 12, 2018 at 10:41

LuCio · Accepted Answer · 2018-06-12 11:02:44Z

133

According to the api-doc:

val list = arrayListOf<Int>()

answered Jun 12, 2018 at 10:44

LuCio

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2 Comments

Isn't an arrayList different from an array in kotlin?

@SMBiggs See SO Q&A

Szymon Chaber · Accepted Answer · 2018-06-12 10:44:29Z

47

I suggest you write

var myList: ArrayList<Int> = arrayListOf()

answered Jun 12, 2018 at 10:44

Szymon Chaber

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val myList = arrayListOf<Int>() reads much better.

What if it's an array, not an arrayList?

you can do this with val value= Array(20) { 0 }