Kotlin arrayListOf()

In Kotlin, the arrayListOf() function is used to create a new ArrayList. An ArrayList is a mutable collection, which means that we can add, remove, or update its elements after it is created.

Syntax:

1. To create an empty ArrayList:

fun arrayListOf(): ArrayList<T>

This creates an empty ArrayList that doesn’t contain any elements.

2. To create an ArrayList with some initial elements:

fun arrayListOf(vararg elements: T): ArrayList<T>

This creates a new ArrayList with the given elements.

Example 1: Create an empty ArrayList

Output :

true
ArrayList : []

Example 2: Create an ArrayList with String elements

Output :

false
ArrayList : [Java, Python, JavaScript]

Example 3: Create an ArrayList with mixed data types

Output :

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

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

Example :

Output :

0
1

The ArrayList class has the following functions: 

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

Example:

Output :

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

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

Example:

Output :

[]
[GeeksforGeeks]

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

Example:

Output :

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

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

Example:

Output :

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

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

Example:

Output :

[Java, Kotlin]
[]

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

Example:

Output :

true

7. 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

Example:

Output :

true

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

Example:

Output :

Kotlin

9. 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.

Example:

Output :

1

10. 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.

Example:

Output :

3

11. 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.

Example:

Output :

true
[Java, Python, Kotlin]

12. 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.

Example:

Output :

true
[Python]

13. 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.

Example:

Output :

Kotlin
[Java, Kotlin, Python]

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

Example:

Output :

[Java, PHP, Kotlin, Python, Kotlin]

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

Example:

Output :

Java
Kotlin
Python
Kotlin

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

Example:

Output :

[Java, Kotlin, Python, Kotlin]

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

Example:

Output :

false

We can use the following way to traverse through an ArrayList.

1. Using for loop with index:

Example:

Output :

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

2. Using for-each loop (element wise):

Output :

Java
Python
Kotlin

3. Using while loop:

Output :

Java
Python
Kotlin

4. Using Iterator:

Output :

Java
Python
Kotlin