Queue in Kotlin

Node.kt

class Node {
    internal var text: String = ""
    internal var nextNode: Node? = null
}

Queue.kt

class Queue {

    var head: Node? = null
    var tail: Node? = null

    fun dequeue(): String? {
        val result: String? = head?.text
        head = head?.nextNode

        if (head == null) {
            tail = head    // empty
        }
        return result
    }

    fun enqueue(value: String) {
        var newNode = Node()
        newNode.text = value
        if (tail != null) {
            tail!!.nextNode = newNode
            tail = newNode
        } else {
            // first node
            tail = newNode
            head = tail
        }
    }

    fun isEmpty(): Boolean {
        return tail == null
    }

    fun size(): Int {
        var size: Int = 0
        var node = head
        while (node != null) {
            size++
            node = node.nextNode
        }

        return size
    }
}

QueueTester.kt

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

//    queue.dequeue()
    checkSize(queue)

    queue.enqueue("Jerry")
    checkSize(queue)

    queue.dequeue()
    checkSize(queue)

    queue.enqueue("Steve")
    queue.enqueue("Norlen")
    queue.enqueue("Jacky")
    queue.enqueue("Lois")
    queue.enqueue("Bruce")

    for (i in queue.size() downTo 1) {
        println("dequeue result = " + queue.dequeue())
    }
}

fun checkSize(queue: Queue) {
    println("Size is = " + queue.size())
    println("Queue is Empty? = " + queue.isEmpty())
}