The **```dart:collection``` library** provides the advance collection support for the Dart language apart from the basic collections already provided by the ```dart:core``` library.

It contains the **```DoubleLinkedQueue<E>``` class** which implements the abstract ```Queue<E>``` class, using a doubly-linked list.

#     
## The ```removeFirst()``` method
The ```DoubleLinkedQueue<E>``` class contains the **```removeFirst()``` method**, which removes and returns the first element of the queue.

>A **queue** is a #key# FIFO: First In First Out #key# data structure.  In a queue, the element that is added first will be deleted first. 
- This method modifies the state of the queue.
- This method throws an unhandled exception if it is called on an empty queue.

## Syntax
```
E removeFirst()
```

## Arguments
- This method does not take any arguments.

## Return values
- This method removes and returns the first element of the queue.
- This is a constant-time operation.




## Code
First, we import the ```dart:collection``` library into our program.

import 'dart:collection'; 
void main() { 
   var animalQueue = DoubleLinkedQueue<String>();
   
   animalQueue.add("Monkey"); 
   animalQueue.add("Lion"); 
   animalQueue.add("Tiger");   
   
   print('Printing Queue Elements');
   print(animalQueue); 

   var elem1 = animalQueue.removeFirst();
   print('Removing ${elem1} from Queue using removeFirst()');

   print('Printing Queue Elements');
   print(animalQueue); 
}  

## Explanation
- We created an instance of a ```DoubleLinkedQueue``` class of type ```String```.
- Next, we added the strings ```"Monkey"```, ```"Lion"```, and ```"Tiger"```  to the queue using the ```add()``` method. 
- The queue elements are displayed as `{Monkey, Lion, Tiger}`, and all the elements are added to the end of the queue because the queue is a FIFO data structure.
- Now, we remove call the ```removeFirst()``` method and store the return value in a variable.
- Then we display the removed item and all the queue elements once more, and we see that ```"Monkey"``` is removed from the queue. The queue elements are displayed using the ```print()``` function of the ```core``` library.

How to remove the first element from a DoubleLinkedQueue in Dart

The removeFirst() method in Dart's DoubleLinkedQueue removes and returns the first element, altering the queue's state, and throws an exception if the queue is empty.