Kotlin Set Interface

Kotlin Set interface is a generic unordered collection of elements. Set interface does not support duplicate elements. This interface is immutable in nature its methods supports read-only functionality of the set.

Set interface uses setOf() function to create the list of object of set interface which contains list of elements.

Set Interface declaration

Properties of Set Interface

Properties	Description
abstract val size: Int	It returns the size of collection.

Functions of Set Interface

Kotlin Set interface has several functions. Some of its functions are mention below.

Functions	Description
abstract fun contains(element: E): Boolean	It checks the mention element is present in this collection. If it contains element, it returns true else returns false.
abstract fun containsAll(elements: Collection<E>): Boolean	It checks all the mention elements of specified collection are present in this collection. If it contains element, it returns true else returns false.
abstract fun isEmpty(): Boolean	It returns true if the collection is empty (contains no elements) otherwise it returns false.
abstract fun iterator(): Iterator<E>	It returns an iterator over the elements of set object.
fun <T> Iterable<T>.all(predicate: (T) -> Boolean): Boolean	It returns true if all the elements matches with given predicate.
fun <T> Iterable<T>.any(): Boolean	It returns true if the collection contains at least one element.
fun <T> Iterable<T>.count(predicate: (T) -> Boolean): Int	It returns the total number of elements matching with given predicate.
fun <T> Iterable<T>.distinct(): List<T>	It returns a list which contains only distinct elements from the given collection.
fun <T> Iterable<T>.drop(n: Int): List<T>	It returns a list which contains all elements except first n elements.
fun <T> Iterable<T>.elementAtOrElse( index: Int, defaultValue: (Int) -> T ): T	It returns an element at given index or result of calling the defaultValue function if the index is out bounds in current collection.
fun <T> Iterable<T>.filter( predicate: (T) -> Boolean ): List<T>	It returns a list which contains only those elements matches with given predicate.
fun <T> Iterable<T>.filterIndexed( predicate: (index: Int, T) -> Boolean ): List<T>	It returns a list which contains only those elements matches with given predicate.
fun <T> Iterable<T>.filterNot( predicate: (T) -> Boolean ): List<T>	It returns a list which contains only those elements which does not matches with given predicate.
fun <T> Iterable<T>.find(predicate: (T) -> Boolean): T?	It returns the first element which matches with given predicate, or null if no such element was found.
fun <T> Iterable<T>.findLast(predicate: (T) -> Boolean): T?	It returns the last element which matches with given predicate, or null if no such element was found.
fun <T> Iterable<T>.first(): T	It returns the first element.
fun <T> Iterable<T>.first(predicate: (T) -> Boolean): T	It returns the first element which matches the given predicate.
fun <T> Iterable<T>.firstOrnull(): T?	It returns the first element or null if collection is empty.
fun <T> Iterable<T>.indexOf(element: T): Int	It returns the first index of given element, or -1 if element does not contains in collection.
fun <T> Iterable<T>.indexOfFirst( predicate: (T) -> Boolean ): Int	It returns the index of first element which matches the given predicate, or -1 if the element does not contains in collection.
fun <T> Iterable<T>.indexOfLast( predicate: (T) -> Boolean ): Int	It returns the index of last element which matches the given predicate, or -1 if the element does not contains in collection.
infix fun <T> Iterable<T>.intersect( other: Iterable<T> ): Set<T>	It returns a set which contains all elements present in both this set and given collection.
fun <T> Collection<T>.isNotEmpty(): Boolean	It returns true if is not empty.
fun <T> Iterable<T>.last(): T	It returns the last element.
fun <T> Iterable<T>.last(predicate: (T) -> Boolean): T	It returns the last element which matches with given predicate.
fun <T> Iterable<T>.lastIndexOf(element: T): Int	It returns the last index of given element, or -1 if element does not exist in collection.
fun <T> Iterable<T>.lastOrnull(): T?	It returns the last element of collection, or null if collection is empty.
fun <T> Iterable<T>.lastOrnull(predicate: (T) -> Boolean): T?	It returns the last element after matching the given predicate, or returns null if no such element found in collection.
fun <T : Comparable<T>> Iterable<T>.max(): T?	It returns the largest element or null if no elements in collection.
fun <T, R : Comparable<R>> Iterable<T>.maxBy( selector: (T) -> R ): T?	It returns the first element yielding the largest value of the given function, or it returns null if there are no elements in collection.
fun <T : Comparable<T>> Iterable<T>.min(): T?	It returns the smallest element or null if there is no element in the collection.
fun <T, R : Comparable<R>> Iterable<T>.minBy( selector: (T) -> R ): T?	It returns the first element which gives the smallest value of the given function or null if there are no elements.
operator fun <T> Set<T>.minus(element: T): Set<T>	It returns a set which contains all the elements of original set except those given element.
operator fun <T> Set<T>.minus(elements: Iterable<T>): Set<T>	It returns a set which contains all the elements of original set except those given elements collection.
operator fun <T> Iterable<T>.minus(element: T): List<T>	It returns a list which contains all the elements of original collection except those contained in the given elements array.
fun <T> Set<T>.minusElement(element: T): Set<T>	It returns a set which contains all the elements of original set except those given element.
fun <T> Iterable<T>.minusElement(element: T): List<T>	It returns a list which contains all the elements of original collection except the first occurrence of the given element.
operator fun <T> Set<T>.plus(element: T): Set<T>	It returns a set of all elements of original set as well as the given element if it is not already present in the set.
operator fun <T> Set<T>.plus(elements: Iterable<T>): Set<T>	It returns a set which contains all the elements of original set as well as the given elements collection which are not already present in the set. The returned set preserves the iteration of element in the same order of the original set.
operator fun <T> Iterable<T>.plus(element: T): List<T>	It returns a list which contains all the elements of the original collection as well as the given element.
fun <T> Set<T>.plusElement(element: T): Set<T>	It returns a set which contains all the elements of the original set as well as the given element.
fun <T> Iterable<T>.plusElement(element: T): List<T>	It returns a list which contains all the elements of the original collection as well as the given element.
fun <T> Iterable<T>.reversed(): List<T>	It returns a list with elements in the reverse order.
fun <T> Iterable<T>.single(): T	It returns the single element, or it throws an exception if the collection has more than one elements or empty.
fun <T> Iterable<T>.singleOrnull(): T?	It returns a single element, or null if the collection has more than one element or it is empty.

Kotlin Set Interface Example 1

Let create an example of declaring and traversing set element using setOf() function. In this example we create a set of Int type non generic and another generic set of Any type.

fun main(args: Array<String>){
    val intSet = setOf(2,6,4,29,4,5)
    val mySet: Set<Any> = setOf(2,6,4,29,4,5,"Ashu","Ajay")
    println(".......print Int set.........")
    for(element in intSet){
        println(element)
    }
    println(".......print Any set.........")
    for(element in mySet){
        println(element)
    }

}

Output:

.......print Int set.........
2
6
4
29
5
.......print Any set.........
2
6
4
29
5
Ashu
Ajay

In the above example we declare element 4 twice in both intSet and mySet but while traversing them they print the element 4 only once. This is because the set interface does not support duplicate elements.

Kotlin Set Interface Example 2 - contains() and containsAll()

The contains() function checks the given element is present in current set or not. If it is contains in the set, the set returns true else returns false. Whereas containsAll() function checks all the elements of collection type are present in the current set or not. If the set contains all elements of collection type it returns true else false.

fun main(args: Array<String>){
    val mySet: Set<Any> = setOf(2,6,4,29,5,"Ashu","Ajay")
    val intSet = setOf(6,4,29)
    println(".......print Any set.........")
    for(element in mySet){
        println(element)
    }
    println("...mySet.contains\"Ashu\"...")
    println(mySet.contains("Ashu"))
    println("...mySet.contains(20)...")
    println(mySet.contains(20))
    println("...mySet.containsAll(intSet)...")
    println(mySet.containsAll(intSet))

}

Output:

.......print Any set.........
2
6
4
29
5
Ashu
Ajay
...mySet.contains"Ashu"...
true
...mySet.contains(20)...
false
...mySet.containsAll(intSet)...
true

Kotlin Set Interface Example 3 - isEmpty() and isNotEmpty()

The isEmpty() function checks the current set is empty. If the set is empty the isEmpty() function returns true otherwise it returns false. And isNotEmpty() checks the current set is not empty. If the set is not empty the isNotEmpty() function returns true else return false.

fun main(args: Array<String>){
    val mySet: Set<Any> = setOf(2,6,4,29,5,"Ashu","Ajay")
    println(".......print Any set.........")
    for(element in mySet){
        println(element)
    }

    println("...mySet.isEmpty()...")
    println(mySet.isEmpty())

    println("...mySet.isNotEmpty()...")
    println(mySet.isNotEmpty())

}

Output:

.......print Any set.........
2
6
4
29
5
Ashu
Ajay
...mySet.isEmpty()...
false
...mySet.isNotEmpty()...
true

Kotlin Set Interface Example 4 - drop()

The drop() function returns all the element except the first n elements of collection.

fun main(args: Array<String>){
    val mySet: Set<Any> = setOf(2,6,4,29,4,5,"Ajay","Ashu","Ajay")
    println(".......print Any set.........")
    for(element in mySet){
        println(element)
    }
    val remainList= mySet.drop(4)
    println(".......print Set after mySet.drop(4).........")
    for(element in remainList){
        println(element)
    }
}

Output:

.......print Any set.........
2
6
4
29
5
Ajay
Ashu
.......print Set after mySet.drop(4).........
5
Ajay
Ashu

Kotlin Set Interface Example 5 - elementAt() and elementAtOrNull()

The elementAt() function return element at given index and elementAtOrNull() function also return the element at given index , but if specified index does not contain element it returns null.

fun main(args: Array<String>){
    val mySet: Set<Any> = setOf(2,6,4,29,4,5,"Ajay","Ashu","Ajay")

    println(".......print Any set.........")
    for(element in mySet){
        println(element)
    }

    println(".......print mySet.elementAt(3).........")
    println(mySet.elementAt(3))

    println(".......print mySet.elementAtOrNull(5).........")
    println(mySet.elementAtOrNull(5))
}

Output:

.......print Any set.........
2
6
4
29
5
Ajay
Ashu
.......print mySet.elementAt(3).........
29
.......print mySet.elementAtOrNull(5).........
Ajay

Next TopicKotlin MutableSet: mutableSetOf()

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Set Interface declaration

Properties of Set Interface

Functions of Set Interface

Kotlin Set Interface Example 1

Kotlin Set Interface Example 2 - contains() and containsAll()

Kotlin Set Interface Example 3 - isEmpty() and isNotEmpty()

Kotlin Set Interface Example 4 - drop()

Kotlin Set Interface Example 5 - elementAt() and elementAtOrNull()

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