ArrayList or mutanleListOf. Strikes me latter is ...

# getting-started

[Ben Edwards]

ArrayList or mutanleListOf. Strikes me latter is better. My understanding is Arraylist specifically uses the Java implementation while mutanleListOf does not specifically use it, it tells kotlin to decide. Although if you are using JVM it will (currently) use the Java class if you are not using JVM (i.e. you are maybe doing iOS implementation) it would choose the appropriate class. So if I was planning on going to KMM in the future ArrayList would have to be changed to mutanleListOf? Would ArrrayList be preferable ever?

[Joffrey]

Usually if you don't specifically need ArrayList, you should stick to the more general mutableListOf and let Kotlin decide, as you said, KMM or not.

Note that ArrayList is defined in common Kotlin code, so it would be available in KMM too anyway, but that's not really the point of using mutableListOf - it's more about generality

[mkrussel]

The only time I would use it is when interacting with a poor third party API that requires ArrayList for the types of parameters.

[mkrussel]

I’ve dealt with APIs that required Vectors, not sure if I’ve ever encountered ArrayList requirements.

[ephemient]

ArrayList has a method to explicitly reserve space for additional elements

[ephemient]

there are a few cases where I can imagine that being useful

[ephemient]

for everything else… just use mutableListOf

[Klitos Kyriacou]

I use ArrayList if I know the initial capacity.

[Joffrey]

In most cases where I know the initial capacity, I can usually build the target list out of a map operation or other functional operators, so I still don't need ArrayList. I haven't needed it directly for quite some time to be frank.

That said, I also haven't needed mutableListOf much either. buildList { ... } usually covers everything that cannot be more efficiently expressed by functional operators

[Ben Edwards]

Thanks, everybody.

[Klitos Kyriacou]

And buildList also allows you to add an initial capacity too.