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Kotlin Lists

A list is a collection that holds values in order. A list made with listOf keeps the same values for its whole life.

A whole list printed

The list holds three names in order. Printing it shows the names inside square brackets.

fun main() {
    val names = listOf("Ana", "Bo", "Cy")
    println(names)
}

One value picked by index

Index 1 picks the second value. The output is that one value alone.

fun main() {
    val names = listOf("Ana", "Bo", "Cy")
    println(names[1])
}

A missing index with getOrNull

Index 9 is past the end of the list. getOrNull gives null instead of stopping the program.

fun main() {
    val names = listOf("Ana", "Bo", "Cy")
    println(names.getOrNull(9))
}

Each value printed by a loop

The for loop visits each value in order. Each visit prints one name.

fun main() {
    val names = listOf("Ana", "Bo", "Cy")
    for (name in names) {
        println(name)
    }
}

Example

fun main() {
    val names = listOf("Ana", "Bo", "Cy")
    println(names.size)
    println(names[0])
    println(names.getOrNull(5))
}

Key points

  • listOf: the call that builds a list from values in order.
  • Use a list index in square brackets to pick one value.
  • The first index is 0.
  • Use getOrNull to ask for an index that may not exist.
  • size: the .size value counts the values in a list.

In this example, the list holds three names. The size prints 3. Index 0 prints Ana, and getOrNull for index 5 prints null.

Note

A list from listOf cannot change after it is built.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Kotlin Playground

Exercise

What does listOf("Ana", "Bo", "Cy") print?