Hi all. How can I create a List with initial capacity in Kotlin similar to Java? It seems the mutableListOf method only has elements parameter.

dineshbob:

MutableList<String>(n, {""})

Thanks Daniil. And it looks like the list has to be initialized inside the lamda itself, right?

Not sure what you meant by initializing, here are the docs: http://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-mutable-list.html

You would have to use the ArrayList constructor:

val list = ArrayList(size)

@jk `MutableList`function was added in 1.1 and works the same as

ArrayList

My point is that the name MutableList just indicates "a list, that is mutable". If they wanted to change the underlying implementation in the future they could do

Thanks @jk @voddan . If the ArrayList is created with an initial size, we can just call add() to add the elements. But if we create

MutableList<String>(n, {""}

then the List is initialized with empty strings. If we call add() to add the elements now, they are added after the empty strings. I see that's one big difference.

@dineshbob i don't think it is a bad practice. You could instantiate an ArrayList without any issue 😉

Kotlin has it's own ArrayList that implements MutableList: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-array-list/index.html

whoa. looks like there are two ArrayList. One for JVM which is type alias to Java's ArrayList, and another one for JS which implements MutableList

Oh I didn't notice that! So on JVM it doesn't implement MutableList?

In this document they say to use the methods such as mutableListOf to create the Lists: https://kotlinlang.org/docs/reference/collections.html @muhil

Yes, using MutableList should be the default when you need a mutable list

Okay. that makes sense. Thanks 🙂

on JVM it doesn't implement MutableList?

It does. The type hierarchy does not depend on the target platform. The types are mapped. Details: http://kotlinlang.org/docs/reference/java-interop.html#mapped-types