Queue

A queue is a type of collection that supports operations at both ends. Data is added to one end and removed from the other, following a “first in, first out” (FIFO) principle.

Syntax

Creating a queue:

Queue queue_name = new Queue();

We can also create a queue from an existing list:

var queue_name = new Queue.from(list_name);

Note: To use a queue in a Dart program, we have to import the dart:collection module. If we don’t do so, then we will see the following error:

Error compiling to JavaScript:
main.dart:6:3:
Error: 'Queue; isn't a type
  Queue<String> example_queue = new Queue<String>();
  ^^^^^
main.dart:6:28:
Error: Method not found: 'Queue'.
  Queue<String> example_queue = new Queue<String>();
                                    ^^^^^
Error: Compilation failed.

Example

In the following example, a queue is created and elements are inserted in the queue using the .add() method:

import 'dart:collection';

void main()
{
  // Creating a queue
  Queue<String> example_queue = new Queue<String>();

  // Printing the default value of example_queue
  print(example_queue);

  // Adding elements to example_queue
  example_queue.add("This");
  example_queue.add("Is");
  example_queue.add("A");
  example_queue.add("Queue");

  // Printing the updated example_queue
  print(example_queue);
}

The above code will result in the following output:

{}
{This, Is, A, Queue}