Queues in Dart

Dart also provides the user to manipulate a collection of data in the form of a queue. A queue is a FIFO (First In First Out) data structure where the element that is added first will be deleted first. It takes the data from one end and removes it from the other end. Queues are useful when you want to build a first-in, first-out collection of data. It is a special case of list implementation of data in Dart.

Creating a Queue in Dart

- Using Constructor

Queue variable_name = new Queue();

- Through Existing List

// With type notation(E)
Queue<E> variable_name = new Queue<E>.from(list_name);

// Without type notation
var variable_name = new Queue.from(list_name);

It must be noted that to use a queue in a dart program you have to import 'dart:collection' module. If you don't do so then you will see the following Error:

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

Example 1: Creating a queue through a constructor and then inserting the elements in it

import 'dart:collection';

void main()
{
      // Creating a Queue
      Queue<String> geek = new Queue<String>(); 
      
      // Printing default value of queue
      print(geek);
      
      // Adding elements in a Queue
      geek.add("Geeks");
      geek.add("For");
      geek.add("Geeks");
      
      // Printing the inserted elements
      print(geek);
}

Output:

{}
{Geeks, For, Geeks}

In the above code queue_name.add(element) is used to add the data in the queue.

Example 2: Creating a queue through a list

import 'dart:collection';

void main()
{
      // Creating a List
      List<String> geek_list = ["Geeks","For","Geeks"];
      
      // Creating a Queue through a List
      Queue<String> geek_queue = new Queue<String>.from(geek_list); 
      
      // Printing the elements
      // in the queue
      print(geek_queue);
}

Output:

{Geeks, For, Geeks}

Functions of Queue in Dart

Dart also provides functions to manipulate queue created in the dart. Some important functions are listed in the table below followed by the example to use them.

Example: Using various functions on Queue in Dart

import 'dart:collection';

void main()
{
      // Creating a Queue
      Queue<String> geek = new Queue<String>(); 
      
      // Printing default value of queue
      print(geek);
      
      // Adding a element and displaying it
      geek.add("Geeks");
      print(geek);
      
      // Adding multiple element and displaying it
      List<String> geek_data = ["For","Geeks"];
      geek.addAll(geek_data);
      print(geek);
      
      // Deleting all the data from queue
      geek.clear();
      print(geek);
      
      // Checking if the queue is empty or not
      print(geek.isEmpty);
      
      // Adding first element
      geek.addFirst("Geeks");
      print(geek);
      
      //Adding Last element
      geek.addLast("For");
      geek.addLast("Geeks");
      print(geek);
        
      // Checking length of the queue
      print(geek.length);
      
      // Removing First Element from queue
      geek.removeFirst();
      print(geek);
      
      // Removing Last element from queue 
      geek.removeLast();
      print(geek);
      
      // Displaying all the elements
      // of the queue
      geek.forEach(print);
}

Output:

{}
{Geeks}
{Geeks, For, Geeks}
{}
true
{Geeks}
{Geeks, For, Geeks}
3
{For, Geeks}
{For}
For

Conclusion

In Dart, queues offer an effective way to manage data collections based on the First In, First Out (FIFO) principle. They are especially useful for handling ordered data that needs to be processed sequentially.

Queues can be created using constructors or initialized from existing lists. To avoid compilation errors, it is essential to import the `dart:collection` module. Dart also provides various functions for manipulating queues, such as adding, removing, and retrieving elements, which enhances the flexibility of data handling.

By understanding queue operations in Dart, developers can create optimized, structured, and efficient applications that require sequential data processing.