How to add an item to an ArrayList in Kotlin?

For people just migrating from java, In Kotlin List is by default immutable and mutable version of Lists is called MutableList.

Hence if you have something like :

val list: List<String> = ArrayList()

In this case you will not get an add() method as list is immutable. Hence you will have to declare a MutableList as shown below :

val list: MutableList<String> = ArrayList()

Now you will see an add() method and you can add elements to any list.