Queue in Scala

15 Oct, 2019
A queue is a first-in, first-out (FIFO) data structure. Scala offers both an immutable queue and a mutable queue. A mutable queue can be updated or extended in place. It means one can change, add, or remove elements of a queue as a side effect. Immutable queue, by contrast, never change.
In Scala, Queue is implemented as a pair of lists. One is used to insert the elements and second to contain deleted elements. Elements are added to the first list and removed from the second list. The two most basic operations of Queue are Enqueue and Dequeue.
Enqueue – Adding an element at the end of the queue.
Dequeue – Deleting an element from the beginning of the queue.
Methods in Queue:
+=: This method is used to add a single element in the end of the queue.++=: This method is used to Insert more than one the element in the end of the queue.clear: Remove all elements from the queue.dequeue: Returns the first element in the queueenqueue: Adds all the elements to the queue.equals: Checks if two queues are structurally identical.front: Returns the first element in the queue.isEmpty: Check if the queue is empty or not.
+=: This method is used to add a single element in the end of the queue.
++=: This method is used to Insert more than one the element in the end of the queue.
clear: Remove all elements from the queue.
dequeue: Returns the first element in the queue
enqueue: Adds all the elements to the queue.
equals: Checks if two queues are structurally identical.
front: Returns the first element in the queue.
isEmpty: Check if the queue is empty or not.
Below are simple Scala programs to demonstrate these operations:
Example 1:
// Scala program for illustrating Queue  // Import Queue import scala.collection.mutable._  // Creating objectobject GfG{     // Main method    def main(args:Array[String])    {        // Initialize a queue        var q1 = Queue(1, 2, 3, 4, 5)                  // Print the elements of queue        print("Queue Elements: ")        q1.foreach((element:Int) => print(element+" "))                   // Print the first element of the queue        var firstElement = q1.front         println("\nFirst element in the queue: "+ firstElement)                   // Enqueue 10 in the queue        q1.enqueue(10)                   // Print the elements of queue        print("Queue Elements after enqueue: ")         q1.foreach((element:Int) => print(element+" "))                  // Dequeue first element from the queue        var deq = q1.dequeue                  // Print the elements of queue        print("\nQueue Elements after dequeue: ")         q1.foreach((element:Int) => print(element+" "))                  // Print the Dequeued element        print("\nDequeued element: " + deq)                  // using isEmpty method        println("\nQueue is empty: "+ q1.isEmpty)    }}
Queue Elements: 1 2 3 4 5 
First element in the queue: 1
Queue Elements after enqueue: 1 2 3 4 5 10 
Queue Elements after dequeue: 2 3 4 5 10 
Dequeued element: 1
Queue is empty: false

Example 2:
// Scala program for illustrating Queue  // Import Queue import scala.collection.mutable._  // Creating objectobject GfG{     // Main method    def main(args:Array[String])    {        // Initialize a queue        var fruits = Queue[String]()                  // Adding elements to the queue        fruits.enqueue("apple")        fruits.enqueue("banana")        fruits.enqueue("mango")        fruits.enqueue("guava")                  // Print the elements of queue        print("Queue Elements: ")        fruits.foreach((element:String) => print(element+" "))                   // Print the first element of the queue        var firstElement = fruits.front         println("\nFirst element in the queue: "+ firstElement)                   // Enqueue pineapple in the queue        fruits.enqueue("pineapple")                   // Print the elements of queue        print("Queue Elements after enqueue: ")         fruits.foreach((element:String) => print(element+" "))                  // Dequeue first element from the queue        var deq = fruits.dequeue                  // Print the elements of queue        print("\nQueue Elements after dequeue: ")         fruits.foreach((element:String) => print(element+" "))                  // Print the Dequeued element        print("\nDequeued element: " + deq)          // Using clear method        println("\nclear the queue: "+ fruits.clear)                  // Using isEmpty method        println("\nqueue is empty: "+ fruits.isEmpty)              }}
Queue Elements: apple banana mango guava 
First element in the queue: apple
Queue Elements after enqueue: apple banana mango guava pineapple 
Queue Elements after dequeue: banana mango guava pineapple 
Dequeued element: apple
clear the queue: ()

queue is empty:true

Picked
Scala
scala-collection
Scala
Writing code in comment?
Please use ide.geeksforgeeks.org,
generate link and share the link here.