Lists
Learn how to create and use lists in Kotlin to store and manipulate multiple values in one data structure.
Collections are a central feature of any programming language. They allow storing multiple values – such as your list of favorite books – in one convenient data structure which can then be stored and accessed with a single variable.
The fundamental collection types you’ll master in the following lessons are:
- Lists
- Sets
- Arrays*
- Maps
*Arrays are not part of the actual Collections API but are included here because they’re also a data structure for storing multiple elements.
Creating a List #
Kotlin provides three convenient functions to initialize lists:
val siUnits = listOf("s", "m", "kg", "A", "K", "mol", "cd") // Creates readonly listval quarks = mutableListOf("up", "down", "charm", "strange", "top", "bottom") // Creates mutable listval physicists = arrayListOf("Albert Einstein", "Isaac Newton") // Creates mutable list
All three functions allow you to add any number of elements (try it out!). The main difference between them is that listOf creates a read-only list whereas mutableListOf creates a mutable list. What does this mean? With read-only lists, you cannot add or remove elements from the list after it’s created. With a mutable list, however, you can.
The code example uses type inference so you can’t see what the data types are. They are:
Function Call Return Type listOf("", ...)List<String>mutableListOf("", ...)MutableList<String>arrayListOf("", ...)ArrayList<String>You can read the type
List<String>as “list of string”. ...