Lists in Kotlin: interface List , interface MutableList , class ArrayList. Functions to create: listOf(...), mutableListOf(...), arrayListOf(...)

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Lists in Kotlin: interface List , interface MutableList , class ArrayList. Functions to create: listOf(...), mutableListOf(...), arrayListOf(...)

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обновлено: 24 September 2026

Kotlin

interface List<E>

interface List<E> is an array (in other words, a collection of elements).
Any element can be gotten by integer index.
You cannot add or delete elements.

Description:

Kotlin library kotlin-stdlib.jar Collections.kt file

interface List<E> : Collection<E> {

Let's look at Functions >> ...

}

To create List<E>, use the function: listOf(...)

Kotlin Example

class Car (val name:String, val price:Int)
{
}

...

// Create List
val allCars:List<Car> = listOf(
     Car("Audi A6", 50000),
     Car("Toyota Camry", 25000),
     Car("Honda Accord", 40000)
)

// We find cars whose price > 20000
val foundItems = allCars.filter { elem ->
     elem.price>20000
}

// Going through all the elements
foundItems.forEach { elem ->
     // show car name and car price on the screen
     println("${elem.name} ${elem.price}")
}

Kotlin

interface MutableList<E>

interface MutableList<E> is an array (in other words, a collection of elements).
Any element can be gotten by integer index.
You can add and remove elements using the add, remove functions.

Description:

Kotlin library kotlin-stdlib.jar Collections.kt file

interface MutableList<E> : List<E>, MutableCollection<E> {

Let's look at Functions >> ...

}

To create MutableList<E>, use the function: mutableListOf(...)

Kotlin Example

class Car (val name:String, val price:Int)
{
}

...

// Create MutableList
val allCars:MutableList<Car> = mutableListOf(
     Car("Audi A6", 50000),
     Car("Toyota Camry", 25000),
     Car("Honda Accord", 40000)
)

allCars.add( Car("Kia Sorento", 32000) )
allCars.add( Car("Hyundai Tucson", 34000) )

allCars.removeIf{elem ->
     elem.name=="Honda Accord"
}

// We find cars whose price > 20000
val foundItems = allCars.filter { elem ->
     elem.price>20000
}

// Going through all the elements
foundItems.forEach { elem ->
     // show car name and car price on the screen
     println("${elem.name} ${elem.price}")
}

Kotlin

class ArrayList<E>

class ArrayList<E> is an array (in other words, a collection of elements).
Any element can be gotten by integer index.
You can add and remove elements using the add, remove functions.

Note!
There is NO class ArrayList <E>in the Kotlin library
Kotlin The library contains only the title. This name references the Java library.

Kotlin TypeAliases.kt file

typealias class ArrayList<E> = java.util.ArrayList<E>

Description:

Java Library java.util file ArrayList.java

class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, Serializable
{

Let's look at Functions >> ...

}

To create ArrayList<E>, use the function: arrayListOf(...)

Kotlin Method 1

val allCars:ArrayList<Car> = arrayListOf(
     Car("Audi A6", 50000),
     Car("Toyota Camry", 25000),
     Car("Honda Accord", 40000)
)

Another way to create we can use constructor ArrayList:

Kotlin Method 2

val allCars:ArrayList<Car> = ArrayList<Car>(
     listOf(
          Car("Audi A6", 50000),
          Car("Toyota Camry", 25000),
          Car("Honda Accord", 40000)
     )
)

Functions listOf(...), mutableListOf(...), arrayListOf(...)

Function

return

Implementation

Kotlin

listOf(...)

Kotlin

List<T>

Java

java.util.ArrayList

Kotlin

mutableListOf(...)

Kotlin

MutableList<T>

Java

java.util.ArrayList

Kotlin

arrayListOf(...)

Kotlin

ArrayList<T>

Java

java.util.ArrayList

Why create ArrayList ?
Answer: As a general rule, you should always give preference to the interface.
Therefore, interface MutableList should be used.

Examples, all interface functions MutableList

Create

mutableListOf(7, 35, 14)
function creates a list and within 3 items
Note! Any number of elements can be written at the time of creation

Kotlin Example 1

val myList1:MutableList<Int> = mutableListOf(7, 35, 14)
// myList1 = 7, 35, 14

Kotlin Example 2

val myList1:MutableList<Int> = mutableListOf(10, 20, 30, 40, 50, 60)
// myList1 = 10, 20, 30, 40, 50, 60

mutableListOf()
The function creates an empty list

Kotlin Example

val myList1:MutableList<Int> = mutableListOf()
// myList1 = 0 elements

number of elements

size
The field contains the number of elements

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35, 14)

val n:Int = myList1.size
// n = 3

isEmpty()
The function returns true if the list is empty

Kotlin Example 1

val myList1:MutableList<Int> = mutableListOf()

val myListEmpty:Boolean = myList1.isEmpty()
// myListEmpty = true

Kotlin Example 2

val myList1:MutableList<Int> = mutableListOf(7, 35, 14)

val myListEmpty:Boolean = myList1.isEmpty()
// myListEmpty = false

Converting a collection to

map{element -> object of new type}
Convert a collection to a different type of element

Kotlin Example

class Car (val name:String, val price:Int)
{
}

class Book (val author:String)
{
}

...

val allCars:MutableList<Car> = mutableListOf(
     Car("Audi A6", 50000),
     Car("Toyota Camry", 25000),
     Car("Honda Accord", 40000)
)

// Convert a collection of Car elements to Book elements
val convertedItems:List<Book> = allCars.map {elem -> Book(elem.name) }

Functions: toList() toSet() toMutableList() toSortedSet() toTypedArray()

View items, search for items

get(index)
Selecting an element by position
index it is a position starting from 0

You can do it like this:
[index]

Kotlin Example 1

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 9)

val element = myList1.get(2)
// element = 14

Kotlin Example 2

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 9)

val element = myList1[2]
// element = 14

find{element -> conditions}
finding one element by conditions
The function returns the
If not found, return null

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 9)

val foundValue = myList1.find{ value -> value==14 || value==7 }
// foundValue = 7

val foundValue = myList1.find{ value -> value==97 }
// foundValue = null

filter{element -> conditions}
Select elements by condition.
A new list is created.

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 9)

// Select elements where the values are greater than 10
val myList2 = myList1.filter { value -> value>10 }
// myList2 = 35, 14 This is a new list
// myList1 = 7, 35, 14, 9 The old list has not changed

subList(indexStart, indexEnd)
Select the elements from the starting to the final position.
A new list is created.
Note! No element is taken in the final position.

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 9, 82)

// Select the elements, from 1 to 3 positions
val myList2 = myList1.subList(1, 3)
// myList2 = 35, 14 This is a new list
// myList1 = 7, 35, 14, 9, 82 The old list has not changed

forEach{element -> Action}
Go through all the elements.

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 9)

myList1.forEach { value ->
// Displaying the value on the screen
println(value)
}

Other functions: single() elementAtOrElse() elementAtOrNull() first() firstOrElse() firstOrNull() take()

replace element

set(index, element)
replace element at the position with the specified element
index it is a position

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 9)

// For position 2, put the number 130
myList1.set(2, 26)
// myList1 = 7, 35, 130, 9
// index=0 index=1 index=2 index=3

Other functions: fill()

Adding Items

add(element)
adding one element to the end

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35)

myList1.add(10)
// myList1 = 7, 35, 10

addAll(array)
adding array of elements to the end

addAll(collection)
adding collection of elements to the end

Kotlin Example 1

val myList1:MutableList<Int> = mutableListOf(7, 35)

val values:Array<Int> = arrayOf(210, 160, 14)
myList1.addAll(values)
// myList1 = 7, 35, 210, 160, 14

Kotlin Example 2

val myList1:MutableList<Int> = mutableListOf(7, 35)

val myList2:Collection<Int> = listOf(400,300,200)
myList1.addAll(myList2)
// myList1 = 7, 35, 400, 300, 200

add(index, element)
adding one element at the specified position
index it is a position

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 9)

// At position 2, add the number 26
myList1.add(2, 26)
// myList1 = 7, 35, 26, 14, 9
// index=0 index=1 index=2 index=3 index=4

addAll(index, collection)
adding collection of elements at the specified position

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(10, 20, 30)

val values:Collection<Int> = listOf(500,600)
myList1.addAll(1, values)
// myList1 = 10, 500, 600, 20, 30

Other functions: addFirst() addLast() plus()

Deleting Items

remove(element)
deleting one element, even if element duplicating

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 7, 21)

val isDeleted = myList1.remove(7)
// isDeleted = true
//myList1 = 35, 14, 7, 21

removeAt(index)
deleting by index

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 9)

val element = myList1.removeAt(1)
// element = 35
// myList1 = 7, 14, 9

removeAll(collection)
to delete only those elements that match the collection

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(10, 20, 30)

val values:Collection<Int> = listOf(10, 30)
myList1.removeAll(values)
// myList1 = 20

retainAll(collection)
delete all elements but retain only those elements that match the collection

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(10, 20, 30)

val values:Collection<Int> = listOf(10, 30)
myList1.retainAll(values)
// myList1 = 10, 30

clear()
deleting all elements

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 9)

val element = myList1.clear()
// myList1 = 0 elements

Other functions: removeFirst() removeFirstOrNull() removeLast() removeLastOrNull() removeIf()

sorting, filtering (selection of elements by condition), grouping and other algorithms

sortBy{element -> Sort field}
sorting all elements

Kotlin Example

val myList1:MutableList<Int> = mutableListOf(7, 35, 14, 9)

// Sorting Ascending
myList1.sortBy { value -> value }
// myList1 = 7, 9, 14, 35

// Sorting Descending
myList1.sortBy { value -> -value }
// myList1 = 35, 14, 9, 7

filter{element -> conditions}
Select elements by condition.
A new list is created.

Kotlin Example

Other functions: binarySearch drop subList() retainAll{ } replaceAll{ } groupBy{ } fold() max() min() intersect() slice() sum() average() zip() sortWith() asReversed() reverse() reversed() shuffle() associateBy{ } associateWith{ } average() chunked() distinct() random() partition{ }

Validating a Collection

Functions: contains() containsAll() all() any()

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