The **``kotlin.collections`` package** is part of Kotlin's standard library. It contains all collection types, such as ``map``, ``list``, ``set``, etc.
The package provides the ``ArrayDeque`` class, a mutable double-ended queue, and uses a dynamic, resizable array as backup storage.


#   
## The `addFirst()` method
The `ArrayDeque` class contains the **`addFirst()` method**, which adds the specified element to the beginning of the queue.

>**```ArrayDeque```** implements the deque data structure using a resizable array. Deque (pronounced as "deck") stands for double-ended queue. This class provides methods to access both ends of a queue.

## Syntax
```kotlin
fun addFirst(element: E)
```

## Arguments
- This method takes an `element` of type `E` as input.

## Return value
- This method does not return any value.



The illustration below shows the `addFirst()` method of the ```ArrayDeque``` class.

fun main() {
    val monthQueue = ArrayDeque<String>()
    
    monthQueue.add("February")  
    monthQueue.add("March")  
    monthQueue.add("April")      
      
    println("Printing Queue elements --")  
    println(monthQueue)
    
    monthQueue.addFirst("January")
    println("Printing Queue elements after calling addFirst() --")     
    println(monthQueue)    
}

## Explanation
- **Line 2**: We create an empty queue named `monthQueue` to store the strings.

- **Lines 4-6**: We add a few months' names to the `monthQueue` object using the `add()` method.

- **Lines 8-9**: We print all the elements present in the queue.

- **Lines 11**: We call the `addFirst()` method and add `"January"` to the start of the queue.

- **Line 12-13**: We print the elements of `monthQueue` after calling the `addFirst()` method. As we can observe, `"January"` is present at the beginning of the printed queue. 

The `ArrayDeque` elements before and after calling `addFirst()` method are displayed using the `println()` function of the ``kotlin.io`` package.

What is the ArrayDeque.addFirst() method in Kotlin?

ArrayDeque's addFirst() method in Kotlin adds an element to the queue's start using a resizable array.

What is the ArrayDeque.addFirst() method in Kotlin?

The addFirst() method

Syntax

Arguments

Return value

Explanation

The `addFirst()` method