The **```kotlin.collections``` package** is part of Kotlin's standard library and contains all collection types, such as ```Map```, ```List```, ```Set```, etc.
The package provides the **```ArrayList``` class**, which is a mutable list that uses a dynamic resizable array as the backing storage.

#    
## The `set()` method
The `ArrayList` class contains the **`set()` method**, which replaces an element at a specified index with the provided input element.

## Syntax
```
fun set(index: Int, element: E): E
```

## Parameters 
- This method takes the integer index and an element to put on that index as input. 

## Return value
- This method returns the element that was previously present at the input index before the `set()` operation.

## Things to note
- `ArrayList` follows the sequence of insertion of elements.

- `ArrayList` is allowed to contain duplicate elements.

The illustration below shows the function of the `set()` method.

# 
## Code
The ```ArrayList``` class is present in the ```kotlin.collection``` package and is imported in every Kotlin program by default.

fun main(args : Array<String>) {
    val sportsList = ArrayList<String>()
    
    sportsList.add("Cricket")
    sportsList.add("Football")  
    sportsList.add("Tennis")  
    sportsList.add("Volleyball")  
    
    println("Printing ArrayList elements--")  
    println(sportsList)  
    val prevElement =  sportsList.set(1,"BasketBall");
    println("Replacing element at index 1 using set() with 'BasketBall',  previous element is : ${prevElement}")
    println("Printing ArrayList elements--")  
    println(sportsList)  

}

#   
## Explanation
- First, we create an empty array list named `sportsList` to store the strings.

- Next, we use the `add()` method to add a few sport names to the ```ArrayList``` object, such as: ```"Cricket"```, ```"Football"```, ```"Tennis"```, and  ```"Volleyball"```.
- Next, we call the  ```set()``` method by passing `1` as the input index and  `BasketBall` as the input value, and it returns `Football` after replacing the element at index `1` - `Football` with `BasketBall`.
- We use the `print()` function of the `kotlin.io` package to display the `Arraylist` elements and result of the `set()` method.



What is the ArrayList.set() method in Kotlin?

The set() method

Syntax

Parameters

Return value

Things to note

Code

Explanation

The `set()` method