Kotlin Array - single() Function

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The Kotlin array single() function is used to check whether single element is available in an array. If an array is empty and more than one element is available, then it returns an error.

This function also takes a predicate and return single element matching the predicate. Otherwise; throws an exception if there is no or more than one matching element.

Exception

Following are the exceptions −

• IllegalArgumentException − If an array contains more than one elements.

• NoSuchElementException − If an array is empty.

Syntax

Following is the syntax of Kotlin array single() function −

fun <T> Array<out T>.single(
   predicate: (T) -> Boolean
): T

Parameters

This function accepts a predicate represents boolean value, true if conditon satisfied. Otherwise; false.

Return value

This function returns an element. Otherwise; an exception.

Example 1

The following is a basic example to demonstrate the use of single() function −

fun main(args: Array<String>) {
   val numbers = arrayOf<Any>(1)   
   // use single
   val single = numbers.single()
   println(single)
}

Output

The above code generate following output −

1

Example 2

Now, Let's see another example, we use single() function with predicate to returns a single element matching with predicate −

fun main(args: Array<String>) {
   val numbers = arrayOf(1, 2, 3, 4, 5)
   try {
      val single = numbers.single { it % 3 == 0 }
      println("Array has a single element: $single")
   } catch (e: NoSuchElementException) {
      println("Array is empty.")
   } catch (e: IllegalArgumentException) {
      println("Array contains more than one element that matches the predicate.")
   }
}

Output

Following is the output −

Array has a single element: 3

Example 3

The below example checks whether in the string array contains exactly one elements having length 4 −

fun main(args: Array<String>) {
   val numbers = arrayOf<String>("tutorialspoint", "Hyderabad", "India")
   try {
      val single = numbers.single { it.length > 4 }
      println("Array has a single element: $single")
   } catch (e: NoSuchElementException) {
      println("Array is empty.")
   } catch (e: IllegalArgumentException) {
      println("Array contains more than one element that matches the predicate.")
   }
}

Output

Following is the output −

Array contains more than one element that matches the predicate.