The **`dart:collection` library** provides the advanced 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 `add()` method
The ```DoubleLinkedQueue<E>``` class contains the **`add()` method**, which adds an element to the end of a queue.

>A **queue** is a FIFO (First In First Out) data structure.  In a queue, the element which is added first will be deleted first. 

### Syntax
```
void add(
E value
)
```

### Arguments
- This method takes a value of type ```E``` as input and adds it to the end of the queue.

### Return value
- This method does not return anything
- This is a constant-time operation




### Code
We first import the ```dart:collection``` library into our program.

import 'dart:collection'; 
void main() { 
   var dayQueue = DoubleLinkedQueue<String>();
   
   dayQueue.add("Sunday"); 
   dayQueue.add("Monday"); 
   dayQueue.add("Tuesday");   
   
   print('Printing Queue Elements');
   print(dayQueue); 
   
}  

##  
### Explanation
- We have created an instance of a ```DoubleLinkedQueue``` class of type ```String```.
- Next, we add a few strings to the queue: ```"Sunday"```, ```"Monday"```, and ```"Tuesday"```,   using the ```add()``` method. 
- Notice that all elements are added to the end of the queue, as the queue is a FIFO data structure.
- The queue elements are displayed using the ```print()``` function of the ```core``` library.


### Output
The program prints the output below and exits:
```
Printing Queue Elements
{Sunday, Monday, Tuesday}
```

How to add an element to a DoubleLinkedQueue in Dart

The add() method

Syntax

Arguments

Return value

Code

Explanation

Output

The `add()` method