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 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. 