#    
## Overview

Let's say we have a `list` containing the `list` type as an element. We can use the **`flatten` method** to create a new list containing all the sub-list elements in this scenario.

## Syntax

```kotlin
fun <T> Iterable<Iterable<T>>.flatten(): List<T>
```
## Arguments 
This method doesn't take any arguments.

## Return value 
This method returns a new list containing all the elements of the sublist of the list on which this method is invoked.

## Code example
The code written below demonstrates how we use the `flatten` method:

fun main() {

  var list = arrayListOf(listOf(1,2), listOf(3,4))
  println("The ArrayList is $list")
  
  val newList = list.flatten()
  println("The flattened list is $newList")
}

## Code explanation



* **Line 3**: We create a new ArrayList with the name `list`, using the `arrayListOf` method. We pass two lists, `listOf(1,2) and listOf(3,4)`, as arguments to the `arrayListOf` method. Hence, we get an `ArrayList` with two list elements as the elements of the `list`.

* **Line 6**: We use the `flatten` method to get a new `list` containing all the elements of the sub-list that are present in the `list`. In our case, the list elements are `[1,2]` and `[3,4]`. These are flattened to `1,2,3,4` and returned as a new list. Hence, we get `[1,2,3,4]` as a result.

How to use the flatten method of the ArrayList in Kotlin

Use Kotlin's flatten method to transform a list of lists into a single list containing all sub-list elements. This method takes no arguments and returns a new list.