Kotlin hashSetOf()

Kotlin HashSet is a generic unordered collection of elements and it does not contain duplicate elements. It implements the set interface. hashSetOf() is a function which returns a mutable hashSet, which can be both read and written. The HashSet class store all the elements using hashing mechanism.

Syntax:

fun <T> hashSetOf(vararg elements: T): HashSet<T>

It returns a new HashSet with the given elements but does not guarantee about the order sequence specified at the storing time.

Example of hashSetOf()

Kotlin

fun main(args: Array<String>)
{

    //declaring a hash set of integers
    val seta = hashSetOf(1,2,3,3);
    //printing first set
    println(seta)

    //declaring a hash set of strings
    val setb = hashSetOf("Geeks","for","geeks");
    println(setb);

}

Output:

[1, 2, 3]
[Geeks, for, geeks] 

Adding and removing elements in hashset –

• We can add elements in a hashset using add() and addAll() functions.
• We can remove an element using remove() function.

Kotlin program of using the add() and remove() method –

Kotlin

fun main(args: Array<String>)
{
    //declaring a hash set of integers
    val seta = hashSetOf<Int>();
    println(seta)

    //adding elements
    seta.add(1)
    seta.add(2)

    //making an extra set to add it in seta
    val newset = setOf(4,5,6)
    seta.addAll(newset)

    println(seta)

    //removing 2 from the set
    seta.remove(2)
    println(seta)
}

Output:

[]
[1, 2, 4, 5, 6]
[1, 4, 5, 6] 

Traversal in hashSet-

We can traverse a hashSet using an iterator in a loop.

Kotlin

fun main(args: Array<String>)
{
    //declaring a hash set of integers
    val seta = hashSetOf(1,2,3,5);

    //traversing in a set using a for loop
    for(item in seta)
        println(item)
}

Output:

1
2
3
5

HashSet Indexing –

Using index functions indexOf() , lastIndexOf() we can get the index of the specified element. And we can also find the elements at some specific index using elementAt() function.

Kotlin program of using index –

Kotlin

fun main(args: Array<String>) {

    val captains = hashSetOf("Kohli","Smith","Root","Malinga","Rohit","Dhawan")

    println("The element at index 2 is: "+captains.elementAt(3))

    println("The index of element is: "+captains.indexOf("Smith"))

    println("The last index of element is: "+captains.lastIndexOf("Rohit"))
}

Output:

The element at index 2 is: Malinga
The index of element is: 4
The last index of element is: 0 

contains() and containsAll() functions –

Both the methods are used to check whether an element is present in the Hashset or not? 
Kotlin program of using contains() and containsAll() function –

Kotlin

fun main(args: Array<String>){
    val captains = hashSetOf(1,2,3,4,"Kohli","Smith",
        "Root","Malinga","Rohit","Dhawan")


    var name = "Rohit"
    println("The set contains the element $name or not?" +
            "   "+captains.contains(name))

    var num = 5
    println("The set contains the element $num or not?" +
            "   "+captains.contains(num))

    println("The set contains the given elements or not?" +
            "   "+captains.containsAll(setOf(1,3,"Dhawan","Warner")))
}

Output:

The set contains the element Rohit or not?   true
The set contains the element 5 or not?   false
The set contains the given elements or not?   false 

Checking equality of empty hash sets and use of isEmpty() functions –

fun <T> hashSetOf(): hashSet<T>

This syntax returns an empty hash set of a specific type.
Kotlin program of using isEmpty() function –

Kotlin

fun main(args: Array<String>) {
    //creating an empty hash set of strings
    val seta = hashSetOf<String>()
    //creating an empty hashset of integers
    val setb =hashSetOf<Int>()


    //checking if set is empty or not
    println("seta.isEmpty() is ${seta.isEmpty()}")

    // Since Empty hashsets are equal

    //checking if two hash sets are equal or not
    println("seta == setb is ${seta == setb}")
}

Output :

seta.isEmpty() is true
seta == setb is true