Hello you guys, So I have a question,Why we can not use `arrayListOf` as parameter , only ArrayList ...

# android

[Sam]

Hello you guys,
So I have a question,Why we can not use arrayListOf as parameter , only ArrayList can accept to use as parameter

1. class CategoriesViewHolder(context: Context,categories:ArrayList<Category>){}
2. val categories = arrayListOf<String>()

Thanks

[gergo]

I might not get what you mean, but ArrayList is a type while arrayListOf is a function to create an ArrayList. You can use arrayListOf to have a default parameter for your method if that's what you are trying to achieve.
fun foo(bar: ArrayList<Int> = arrayListOf()){}

[Sam]

Screen Shot 2019-09-10 at 3.59.05 PM.png

[gergo]

still, arrayListOf is a function to create an ArrayList, it's not a type

[gergo]

if you want to add any number of elements to the method via commas, then you may want to use vararg

[gergo]

fun foo(vararg bar: String){
bar.forEach {
}
}

[gergo]

caller side: foo("a","b")

[wasyl]

Henry, it’s the same difference as listOf<X> and List<X>. Also the same difference as Java’s List<X> and ArrayList<X>() - the type and the constructor

[Sam]

Thanks you guys :))))