Kotlin List maxOfWithOrNull()
Syntax & Examples

Syntax of List.maxOfWithOrNull()

The syntax of List.maxOfWithOrNull() extension function is:

fun <T, R> Iterable<T>.maxOfWithOrNull( comparator: Comparator<in R>, selector: (T) -> R ): R?

This maxOfWithOrNull() extension function of List returns the largest value according to the provided comparator among all values produced by selector function applied to each element in the collection or null if there are no elements.


✐ Examples

1 Example

In this example,

  • We create a list named list containing the numbers [3, 1, 4, 1, 5, 9, 2, 6].
  • We apply maxOfWithOrNull() function with a custom comparator to find the maximum value.
  • The selector function { it } returns each element as it is.
  • Since the list is not empty, the maximum value is determined using the comparator.
  • The maximum value, which is 9, is stored in result.
  • Finally, we print the value of result to standard output using the print statement.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf(3, 1, 4, 1, 5, 9, 2, 6);
    val result = list.maxOfWithOrNull(Comparator.comparing { it }) { it };
    print(result);
}

Output

9

2 Example

In this example,

  • We create a list named list containing the characters ['a', 'p', 'p', 'l', 'e'].
  • We apply maxOfWithOrNull() function with the natural order comparator to find the maximum value.
  • The selector function { it } returns each character as it is.
  • Since the list is not empty, the maximum value is determined using the natural order comparator.
  • The maximum value, which is 'p', is stored in result.
  • Finally, we print the value of result to standard output using the print statement.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf('a', 'p', 'p', 'l', 'e');
    val result = list.maxOfWithOrNull(Comparator.naturalOrder()) { it };
    print(result);
}

Output

p

3 Example

In this example,

  • We create a list named list containing the strings ['apple', 'banana', 'orange', 'grape'].
  • We apply maxOfWithOrNull() function with a comparator based on the length of the strings to find the string with the maximum length.
  • The selector function { it } returns each string as it is.
  • Since the list is not empty, the string with the maximum length is determined using the length-based comparator.
  • The string with the maximum length, which is 'banana', is stored in result.
  • Finally, we print the value of result to standard output using the print statement.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf("apple", "banana", "orange", "grape");
    val result = list.maxOfWithOrNull(compareBy { it.length }) { it };
    print(result);
}

Output

banana

Summary

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