Queue

A Queue is a collection interface in Kotlin that represents a data structure that stores elements in a linear order, and follows the First In, First Out (FIFO) principle. This means that the first element added to the queue will be the first one to be removed.

Creating a Queue

In Kotlin, a queue can be created using the Queue interface:

val queue: Queue<Type> = Collection()

• queue is a variable that is of type Queue.
• Type is the data type of the elements within the queue.
• Collection is the collections class that is used to implement the queue. Some possible implementations include a LinkedList, ArrayDeque, and PriorityQueue.

Below, a queue of string elements is created using an instance of the LinkedList collection:

val queue: Queue<String> = LinkedList()

Adding Elements to a Queue

The .add() method can be used to add elements to a queue:

import java.util.*

fun main() {
  // Create a queue of strings
  val queue: Queue<String> = LinkedList()

  // Add elements to the queue
  queue.add("apple")
  queue.add("banana")
  queue.add("orange")
  println(queue)
}

The output for the above code will be:

[apple, banana, orange]

Removing Elements from a Queue

The .remove() method can be used to remove elements from a queue:

import java.util.*

fun main() {
  // Create a queue of strings
  val queue: Queue<String> = LinkedList()

  // Add elements to the queue
  queue.add("apple")
  queue.add("banana")
  queue.add("orange")

  println(queue)

  val a = queue.remove()
  val b = queue.remove()
  val c =queue.remove()

  println(queue)
  print(a,b,c)
}

fun print(a: String, b: String, c: String) {
  println("First element removed is: $a ")
  println("Second element removed is: $b ")
  println("Third element removed is: $c ")
}

The output for the above code will be:

[apple, banana, orange]
[]
First element removed is: apple
Second element removed is: banana
Third element removed is: orange

In the above code, the elements were removed from the queue using .remove() method. In addition, a variable was created to hold each element that was removed.

Peeking at Elements in a Queue

The .peek() method can be used to print out the first element in a queue:

import java.util.*

fun main() {
  val queue: Queue<String> = LinkedList()

  queue.add("apple")
  queue.add("banana")
  queue.add("orange")

  println(queue)

  val frontElement = queue.peek()
  println("The front element peeked is: $frontElement")
}

The output for the above code will be:

[apple, banana, orange]
The front element peeked is: apple