Kotlin provides different types of collections to store data. The main types are:
Let's take a look at each type in more detail.
Arrays are used to store a fixed-size sequential collection of elements. You can create an array in Kotlin using the arrayOf() function:
val numbers = arrayOf(1, 2, 3, 4, 5)
The arrayOf() function takes a variable number of arguments, so you can also create an empty array using:
val emptyArray = arrayOf<Any>() // creates an empty array of type Any
If you know the size of the array you want to create, you can use the arrayOfNulls() function:
val nullArray = arrayOfNulls<String>(5) // creates an array of size 5 with null elements
You can access elements in an array using their index, which starts at 0:
val numbers = arrayOf(1, 2, 3, 4, 5)
numbers[0] // returns 1
numbers[1] // returns 2
numbers[2] // returns 3
numbers[3] // returns 4
numbers[4] // returns 5
You can also use the for loop to iterate over all the elements in an array:
for (number in numbers) {
println(number)
}
Lists are used to store a variable-size sequential collection of elements. You can create a list in Kotlin using the listOf() function:
val numbers = listOf(1, 2, 3, 4, 5)
The listOf() function takes a variable number of arguments, so you can also create an empty list using:
val emptyList = listOf<Any>() // creates an empty list of type Any
You can access elements in a list using their index, which starts at 0:
val numbers = listOf(1, 2, 3, 4, 5)
numbers[0] // returns 1
numbers[1] // returns 2
numbers[2] // returns 3
numbers[3] // returns 4
numbers[4] // returns 5
You can also use the for loop to iterate over all the elements in a list:
for (number in numbers) {
println(number)
}
Sets are used to store a variable-size collection of unique elements. You can create a set in Kotlin using the setOf() function:
val numbers = setOf(1, 2, 3, 4, 5)
The setOf() function takes a variable number of arguments, so you can also create an empty set using:
val emptySet = setOf<Any>() // creates an empty set of type Any
You can iterate over all the elements in a set using the for loop:
for (number in numbers) {
println(number)
}
Maps are used to store a variable-size collection of key-value pairs. You can create a map in Kotlin using the mapOf() function:
val numbers = mapOf("one" to 1, "two" to 2, "three" to 3)
The mapOf() function takes a variable number of arguments, so you can also create an empty map using:
val emptyMap = mapOf<Any, Any>() // creates an empty map of type Any to Any
You can access the value of a map using the key:
numbers["one"] // returns 1
numbers["two"] // returns 2
numbers["three"] // returns 3
You can also iterate over all the key-value pairs in a map using the for loop:
for ((key, value) in numbers) {
println("$key -> $value")
}
In this post, we looked at the different types of collections in Kotlin: arrays, lists, sets, and maps. We saw how to create each type of collection and how to access and iterate over the elements in each collection.