Clear a List in Kotlin

This article explores different ways to clear a mutable list in Kotlin.

1. Using `clear()` function

The standard operation to empty a list is using the clear() function, which efficiently removes all elements from it. This is the best approach in terms of performance. Note that this doesn’t work on unmodifiable lists.

fun main() {

val input = (1..5).toMutableList()

input.clear()

println(input) // []

}

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2. Using `removeAll()` function

We can also use the removeAll() function to remove all elements from a mutable list, that matches with any of the elements in the specified input. A typical invocation for this method would look like below to clear a list:

fun main() {

val input = (1..5).toMutableList()

input.removeAll(input)

println(input) // []

}

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3. Using `remove()` function

The idea is to get a copy of elements in the list and call the remove() function for each element. The copy of the list is used to avoid ConcurrentModificationException, since concurrent modification of the list is not allowed while iterating over it.

fun main() {

val input = (1..5).toMutableList()

input.toList().forEach { input.remove(it) }

println(input) // []

}

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4. Using `Iterator.remove()` function

The iterator’s remove() function doesn’t throw ConcurrentModificationException when some thread modifies the collection while another thread is iterating over it. It can be used as follows:

fun main() {

val input = (1..5).toMutableList()

val it = input.listIterator()

while (it.hasNext()) {

it.next()

it.remove()

}

println(input) // []

}

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That’s all about clearing a mutable list in Kotlin.

1. Using clear() function

2. Using removeAll() function

3. Using remove() function

4. Using Iterator.remove() function

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1. Using `clear()` function

2. Using `removeAll()` function

3. Using `remove()` function

4. Using `Iterator.remove()` function