Initialize a set in Kotlin
This article explores different ways to initialize a set in Kotlin.
1. Using Copy Constructor
You can initialize a set with elements of another collection. The idea is to use a copy constructor that accepts another collection. Note that any duplicates in the list will be silently discarded.
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fun main() { val set: MutableSet<Int> = HashSet(listOf(1, 2, 3)) println(set) // [1, 2, 3] } |
2. Using toSet() function
Alternatively, you can call the toSet() function that accumulates the input elements into an unmodifiable instance of Set.
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fun main() { val set: Set<Int> = (1..3).toSet() println(set) // [1, 2, 3] } |
It can be called upon another collection or an array. Here’s an example using a list:
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fun main() { val set: Set<Int> = listOf(1, 2, 3).toSet() println(set) // [1, 2, 3] } |
If you need a mutable instance of a set, you can use the toMutableSet() function.
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fun main() { val set: MutableSet<Int> = arrayOf(1, 2, 3).toMutableSet() println(set) // [1, 2, 3] } |
3. Using setOf() function
Kotlin provides a convenient way to create instances of Set with small numbers of elements with setOf() function. The setOf() function creates an immutable instance of Set, while mutableSetOf() function creates a mutable instance of it.
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fun main() { val set: Set<Int> = setOf(1, 2, 3) println(set) // [1, 2, 3] } |
4. Using addAll() function
You can initialize a MutableSet later with all elements of a collection or an array using the addAll() function.
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fun main() { val set: MutableSet<Int> = HashSet() set.addAll(1..3) println(set) // [1, 2, 3] } |
5. Using Double Brace Initialization
Although not recommended, you can use Double Brace Initialization in Kotlin, which creates an anonymous inner class with just an instance initializer in it.
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fun main() { val set: HashSet<Int?> = object : HashSet<Int?>() { init { add(1) add(2) add(3) } } println(set) // [1, 2, 3] } |
That’s all about initializing a set in Kotlin.
Thanks for reading.
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