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

The `ArrayList` class contains the **`lastIndexOf()` method**, which returns the index of the last occurrence of the specified element in the list and -1 if the element is not present in the list.
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## Syntax
```
fun lastIndexOf(element: E): Int
```

## Arguments 
- This method takes the element to search as input.

## Return value
- It returns the last index of the element in the list and -1 if the input element is not present.

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

- It is allowed to contain duplicate elements.

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

fun main(args : Array<String>) {
    val sportsList = ArrayList<String>()
    
    sportsList.add("Cricket")
    sportsList.add("Football")
    sportsList.add("Tennis")  
    sportsList.add("Football")  
    sportsList.add("Racing")      
    println("Printing ArrayList elements --")  
    println(sportsList)
    
    var lastIndex = sportsList.lastIndexOf("Football")
    println("Last Index of 'Football' is ${lastIndex}")
    lastIndex = sportsList.lastIndexOf("Hockey")
    println("Last Index of 'Hockey' is ${lastIndex}")
}

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## Explanation
- Line 2: We create an empty array list named `sportsList` to store the strings.

- Line 4 to 7: We add a few sport names to the `ArrayList` object using the `add()` method, such as: `"Cricket"`, `"Football"`, `"Tennis"`, `"Football"`, and `"Racing"`.

- Line 11: We call the `lastIndexOf()` method and pass the input string as `"Football"`. It returns 3 as `"Football"` exists twice, first at index 1 and last at index 3 in the list.

- Line 13: We call the `lastIndexOf()` method and pass the input string as `"Hockey"`. It returns -1, as `"Hockey"` does not exist in the list.

The `ArrayList` elements and result of the `lastIndexOf()` method are displayed using the `println()` function of the `kotlin.io` package.

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

ArrayList's lastIndexOf() in Kotlin returns the last index of an element or -1 if not found.