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?

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 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. 