Kotlin Array - all() Function

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The Kotlin array all() function is used to check all the elements satisfy the given predicate. If they do, it returns true; otherwise, it returns false.

If the array does not contains any elements, the function returns true because there are no elements in it that do not match the predicate.

An important use case of this function is to check whether an array is consistent with the same type of objects in it.

Syntax

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

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

Parameters

This function accepts apredicateas a parameter, which is a lambda function that takes an element of type T.

Return value

This function returns a boolean value: true if all elements in the array satisfy the predicate; otherwise, false.

Example 1

Following is the basic example, we use the all() function to check all the element is of same type or not −

fun main(args: Array<String>) {
   var array = Array(10) { i -> i}
   var result = array.all() {
      i -> i is Int
   }
   if (result == true){
      println("The array is of type integer")
   }        
   else{
      println("The array is not of type integer")
   }        
}

Output

Following is the output −

The array is of type integer

Example 2

Now, let's see another example. Here, we use the all() function to check all the element is positive, or even −

fun main() {
   val numbers = arrayOf(1, 2, 3, 4, 5)

   // Check if all elements in the array are greater than 0
   val areAllPositive = numbers.all { it > 0 }
   println("Are all numbers positive? $areAllPositive")

   // Check if all elements in the array are even
   val areAllEven = numbers.all { it % 2 == 0 }
   println("Are all numbers even? $areAllEven")
}

Output

Following is the output −

Are all numbers positive? true
Are all numbers even? false

Example 3

The example below checks whether the length of each element in a string array is at-least 1 −

fun main(args: Array<String>) {
   var array = arrayOf("Hi", "", "Sample", " Bye")

   var result = array.all {
      i -> i.length >= 1
   }
   if (result == true){
      println("All the values in the array have their string length of more than or equal to 1")
   }        
   else{
     println("All the values in the array don't have their string length of more than or equal to 1")
   }        
}

Output

Following is the output −

All the values in the array don't have their string length of more than or equal to 1