Kotlin Tutorials

Kotlin Set toHashSet()
Syntax & Examples

toHashSet() extension function

The toHashSet() extension function in Kotlin returns a new HashSet containing all the elements of the collection.

Syntax of toHashSet()

The syntax of Set.toHashSet() extension function is:

fun <T> Set<T>.toHashSet(): HashSet<T>

This toHashSet() extension function of Set returns a new HashSet of all elements.

Return Type

Set.toHashSet() returns value of type HashSet.


✐ Examples

1 Converting a set of integers to a HashSet

Using toHashSet() to convert a set of integers to a HashSet.

For example,

  1. Create a set of integers.
  2. Use toHashSet() to convert the set to a HashSet.
  3. Print the resulting HashSet.

Kotlin Program

fun main() {
    val numbers = setOf(1, 2, 3, 4, 5)
    val hashSet = numbers.toHashSet()
    println(hashSet)
}

Output

[1, 2, 3, 4, 5]

2 Converting a set of strings to a HashSet

Using toHashSet() to convert a set of strings to a HashSet.

For example,

  1. Create a set of strings.
  2. Use toHashSet() to convert the set to a HashSet.
  3. Print the resulting HashSet.

Kotlin Program

fun main() {
    val strings = setOf("one", "two", "three")
    val hashSet = strings.toHashSet()
    println(hashSet)
}

Output

[one, two, three]

3 Converting a set of custom objects to a HashSet

Using toHashSet() to convert a set of custom objects to a HashSet.

For example,

  1. Create a data class.
  2. Create a set of custom objects.
  3. Use toHashSet() to convert the set to a HashSet.
  4. Print the resulting HashSet.

Kotlin Program

data class Person(val name: String, val age: Int)

fun main() {
    val people = setOf(Person("Alice", 30), Person("Bob", 25), Person("Charlie", 35))
    val hashSet = people.toHashSet()
    println(hashSet)
}

Output

[Person(name=Alice, age=30), Person(name=Bob, age=25), Person(name=Charlie, age=35)]

Summary

In this Kotlin tutorial, we learned about toHashSet() extension function of Set: the syntax and few working examples with output and detailed explanation for each example.