Kotlin arrayListOf()

The arrayList() is function of Kotlin ArrayList class, which is used to create a new ArrayList. ArrayList is mutable which means that we can modify the content of ArrayList. 

Syntax:

fun  arrayListOf()

It is used to create an empty new ArrayList.

fun  arrayListOf(vararg elements: T)

It is used to create a new ArrayList with provided elements. 

Example 1: Kotlin program to make new empty ArrayList.

Java

fun main(args : Array<String>)
{
    var arrList
        = arrayListOf<String>() println(arrList.isEmpty())
            println("ArrayList : ${arrList}")
}

Output :

true
ArrayList : []

Example 2: Kotlin program to make new ArrayList with String elements

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Python",
                                      "JavaScript")
        println(arrList.isEmpty())
            println("ArrayList : ${arrList}")
}

Output :

false
ArrayList : [Java, Python, JavaScript]

Example 3: Kotlin program to make new ArrayList with elements of any data type

Java

fun main(args : Array<String>)
{
    var arrList
        = arrayListOf<Any>(1, 2, 3, "GeeksforGeeks", 100.0)
            println(arrList.isEmpty())
                println("ArrayList : ${arrList}")
}

Output :

false
ArrayList : [1, 2, 3, GeeksforGeeks, 100.0]

Property

ArrayList in kotlin has one property i.e. size. It returns the number of element in the ArrayList. 

Example :

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>();
    println(arrList.size);
    arrList.add("GeeksforGeeks");
    println(arrList.size);
}

Output :

0
1

Functions

The ArrayList class has the following functions: 

add(element): This function is used to add the specified element to the ArrayList. 

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Python");
    println(arrList);
    arrList.add(0, "Kotlin");
    println(arrList);
}

Output :

[Java, Python]
[Kotlin, Java, Python]

add(index, element): This function is used to add the element to the provided index of ArrayList. 

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>();
    println(arrList);
    arrList.add("GeeksforGeeks");
    println(arrList);
}

Output :

[]
[GeeksforGeeks]

addAll(elementCollection): This function is used to add the specified collection of elements to the ArrayList. 

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Kotlin");
    println(arrList);
    arrList.addAll(listOf("Python", "JavaScript"));
    println(arrList);
}

Output :

[Java, Kotlin]
[Java, Kotlin, Python, JavaScript]

addAll(index, elementCollection): This function is used to add the specified collection of elements to the ArrayList at provided index. 

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Kotlin");
    println(arrList);
    arrList.addAll(1, listOf("Python", "JavaScript"));
    println(arrList);
}

Output :

[Java, Kotlin]
[Java, Python, JavaScript, Kotlin]

clear(): This function is used to remove all the elements from the ArrayList. 

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Kotlin");
    println(arrList);
    arrList.clear();
    println(arrList);
}

Output :

[Java, Kotlin]
[]

contains(element): This function is used to check whether an element exists in the ArrayList. It returns either true, if found, otherwise false

Java

fun main(args : Array<String>) {
    var arrList = arrayListOf<String>("Java", "Kotlin");
    println(arrList.contains("Kotlin"));
}

Output :

true

containsAll(elementCollection): This function is used to check whether a collection of elements exists in the ArrayList. It returns either true, if found, otherwise false

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>(
        "Java", "Kotlin", "Python", "JavaScript");
    var checkList = listOf("Python", "Java");
    println(arrList.containsAll(checkList));
}

Output :

true

get(index): This function is used to retrieve an element at the specified index from the ArrayList 

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>(
        "Java", "Kotlin", "Python", "JavaScript");
    println(arrList.get(1));
}

Output :

Kotlin

indexOf(element) This function returns the index of the first occurrence of the specified element in the ArrayList. If element is not present in the ArrayList, then it returns -1.

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Kotlin",
                                      "Python", "Kotlin");
    println(arrList.indexOf("Kotlin"));
}

Output :

1

lastIndexOf(element) This function returns the index of the last occurrence of the specified element in the ArrayList. If the element is not present in the ArrayList, then it returns -1.

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Kotlin",
                                      "Python", "Kotlin");
    println(arrList.lastIndexOf("Kotlin"));
}

Output :

3

remove(element) This function is used to remove a single instance of the specified element from the ArrayList. It returns true, if the element was present in the ArrayList and is removed, otherwise false.

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Kotlin",
                                      "Python", "Kotlin");
    println(arrList.remove("Kotlin"));
    println(arrList);
}

Output :

true
[Java, Python, Kotlin]

removeAll(elementCollection) This function is used to remove collection of element from the ArrayList. It returns true, if the element collection was removed, otherwise false.

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Kotlin",
                                      "Python", "Kotlin");
    var delList = listOf("Java", "Kotlin");
    println(arrList.removeAll(delList));
    println(arrList);
}

Output :

true
[Python]

removeAt(index): This function is used to remove an element by its position in the ArrayList. It returns true, if the element collection was removed, otherwise false.

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Kotlin",
                                      "Python", "Kotlin");
    println(arrList.removeAt(3));
    println(arrList);
}

Output :

Kotlin
[Java, Kotlin, Python]

set(index, element) This function is used to add an element to the specified position in the ArrayList. 

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Kotlin",
                                      "Python", "Kotlin");
    arrList.add(1, "PHP");
    println(arrList);
}

Output :

[Java, PHP, Kotlin, Python, Kotlin]

toArray() This function is used to convert the ArrayList to an array of type Array. 

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Kotlin",
                                      "Python", "Kotlin");
    var arr = arrList.toArray();
    for (i in arr) {
        println(i);
    }
}

Output :

Java
Kotlin
Python
Kotlin

toString() This function is used to get the string representation of the ArrayList object. 

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>("Java", "Kotlin",
                                      "Python", "Kotlin");
    var arr = arrList.toString();
    println(arr);
}

Output :

[Java, Kotlin, Python, Kotlin]

isEmpty() This function returns true if the ArrayList is empty otherwise true

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>(
        "Java", "Kotlin", "Python", "JavaScript");
    println(arrList.isEmpty());
}

Output :

false

Traversal of the ArrayList

We can use the following way to traverse through an ArrayList. Using for loop (index wise)

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>(
        "Java", "Python", "JavaScript", "Kotlin");
    for (index in 0..arrList.size-1) {
        println("${index} => ${arrList.get(index)}");
    }
}

Output :

0 => Java
1 => Python
2 => JavaScript
3 => Kotlin

Using for loop (element wise)

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>(
        "Java", "Python", "JavaScript", "Kotlin");
    for (value in arrList) {
        println(value);
    }
}

Output :

Java
Python
JavaScript
Kotlin

Using while loop

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>(
        "Java", "Python", "JavaScript", "Kotlin");
    var i = 0;
    while (i < arrList.size) {
        println(arrList.get(i)) i++;
    }
}

Output :

Java
Python
JavaScript
Kotlin

Using Iterator

Java

fun main(args : Array<String>)
{
    var arrList = arrayListOf<String>(
        "Java", "Python", "JavaScript", "Kotlin");
    var itr = arrList.iterator();
    while (itr.hasNext()) {
        println(itr.next());
    }
}

Output :

Java
Python
JavaScript
Kotlin