Dart Queues

A queue is a user-defined collection of data. It is based on the FIFO principle ( First In First Out ) which implies that the element to be inserted first, will be deleted first.

A queue has two ends =  front and rear. Elements are inserted at one end and deleted from the other end.

Note : Don’t forget to import ‘ dart : collection ’ module in the Dart program containing queue.

In Dart, queue can be created using following two methods :

1. Using queue( ) constructor
2. Using existing list

Creating a queue using constructor

Dart provides an in-built constructor Queue( ) to create the data structure queue.

Implementation = Queue queue_name =  new Queue(  ) ;

Program

import 'dart:collection' ;
  
void main( )
{
    // declaring queue using queue( ) constructor
    Queue< String > que = new Queue< String >( ) ; 
    
    // printing the elements of the queue. 
    // Nothing will be printed as queue is empty as of now
    print( que ) ;
    
    // initializing queue with the string elements
    que.add( " This " ) ;
    que.add( " is " ) ;
    que.add( " a " ) ;
    que.add( " Queue " ) ;
  
    // printing the elements of the queue
    print( que ) ;
}

Output :

{ }
{ This, is, a, Queue }

Creating a queue using existing list

Program

import 'dart:collection' ;
void main( )
{
  // creating a list with string elements
  List< String > queue_list = [ " This ", " creates ", " queue ", "  
  using ", " existing ", " list " ] ;
    
  // Creating a Queue using an existing list
  Queue< String > que = new Queue< String >.from( queue_list ) ; 
 
  // Printing the elements of the queue
  print( que ) ;
}

Output :

{ This, creates, queue, using, existing, list }

Functions of Queue in Dart

There are some functions provided by Dart to manipulate queues. Some of the functions are :

Sr.No	Function Syntax	Description of the Function
1.	queue_name.add ( element )	This function adds the element to the queue from the front end.
2.	queue_name.addAll( collection_name )	This function adds all the elements passed in the place of collection_name (generally List) as an argument.
3.	queue_name.addFirst( element )	This function adds the element in the queue at the beginning from the front.
4.	queue_name.addLast( element )	This function adds the element in the queue at the end from the rear end.
5.	queue_name.clear( )	This function clears the queue by deleting all the elements from the queue.
6.	queue_name.first( )	This function returns the first element of the queue from the beginning.
7.	queue_name.forEach( f ( element ) )	This function returns all the elements present in the queue.
8.	queue_name.isEmpty	This function checks if the queue is empty or not and accordingly returns true or false.
9.	queue_name.length	This function calculates the length of the queue and returns the same.
10.	queue_name.removeFirst( )	This function deletes the first element from the queue.
11.	queue_name.removeLast( )	This function deletes the last element from the queue.

Program

import 'dart:collection' ;




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




  //printing the values of queue
  print( " \n Values of the Queue : " ) ;
  print( str ) ;




  // checking length of the queue str
  print( " \n Length of the Queue : " ) ;
  print( str.length ) ;




  // adding a single element to the queue
  str.add( " \n Hello " ) ;




  // printing the values of the queue
  print( " \n Values of the Queue : " ) ;
  print( str ) ;




  // checking length of the queue str
  print( " \n Length of the Queue : " ) ;
  print( str.length ) ;




  // deleting the whole queue str
  str.clear( ) ;
  print( " \n Values of the Queue : "  ) ;
  print( str ) ;




  // check if the queue str is empty or not
  print( " \n Queue is Empty ? " ) ;
  print( str.isEmpty ) ;




  // adding first element in the beginning of the queue str
  str.addFirst( " Java " ) ;
  print( " \n Values of the Queue : " ) ;
  print( str ) ;




  //Adding the last element in the queue str
  str.addLast( " Tpoint " ) ;
  print( " \n Values of the Queue : " ) ;
  print( str ) ;




  // removing the first element of the queue str
  str.removeFirst( ) ;
  print( " \n Values of the Queue : " ) ;
  print( str ) ;




  // remving the last element of the queue str
  str.removeLast( ) ;
  print( " \n Values of the Queue : " ) ;
  print( str ) ;




  // printing the whole queue str
  print( " \n Values of the Queue : " ) ;
  str.forEach( print ) ;
}

Output :

Values of the Queue : 
{}
 
 Length of the Queue : 
0
 
 Values of the Queue : 
{ 
 Hello }
 
 Length of the Queue : 
1
 
 Values of the Queue : 
{}
 
 Queue is Empty ? 
true
 
 Values of the Queue : 
{ Java }
 
 Values of the Queue : 
{ Java ,  Tpoint }
 
 Values of the Queue : 
{ Tpoint }
 
 Values of the Queue : 
{}
 
 Values of the Queue :