Level order traversal using queue in scala

Scala program for Level order traversal using queue. Here more information.

/*
  Scala program for
  Level order tree traversal using queue
*/
// Create Q node
class QNode(var data: TreeNode,
	var next: QNode)
{
	def this(node: TreeNode)
	{
		this(node, null);
	}
}
// Binary Tree Node
class TreeNode(var data: Int,
	var left: TreeNode,
		var right: TreeNode)
{
	def this(data: Int)
	{
		// Set node value
		this(data, null, null);
	}
}
class MyQueue(var head: QNode,
	var tail: QNode,
		var count: Int)
{
	def this()
	{
		this(null, null, 0)
	}
	def size(): Int = {
		return this.count;
	}
	def isEmpty(): Boolean = {
		return this.count == 0;
	}
	// Add new node of queue
	def enqueue(value: TreeNode): Unit = {
		// Create a new node
		var node: QNode = new QNode(value);
		if (this.head == null)
		{
			// Add first element into queue
			this.head = node;
		}
		else
		{
			// Add node at the end using tail
			this.tail.next = node;
		}
		this.count += 1;
		this.tail = node;
	}
	// Delete a element into queue
	def dequeue(): Unit = {
		if (this.head == null)
		{
			// Empty Queue
			return;
		}
		// Visit next node
		this.head = head.next;
		this.count -= 1;
		if (this.head == null)
		{
			// When deleting a last node of linked list
			this.tail = null;
		}
	}
	// Get front node
	def peek(): TreeNode = {
		if (this.head == null)
		{
			return null;
		}
		return this.head.data;
	}
}
class BinaryTree(var root: TreeNode)
{
	def this()
	{
		this(null)
	}
	def levelOrder(): Unit = {
		if (this.root != null)
		{
			var q: MyQueue = new MyQueue();
			// Add first node
			q.enqueue(this.root);
			var node: TreeNode = this.root;
			while (q.isEmpty() == false && node != null)
			{
				if (node.left != null)
				{
					// Add left child node
					q.enqueue(node.left);
				}
				if (node.right != null)
				{
					// Add right child node
					q.enqueue(node.right);
				}
				// Display level node
				print("  " + node.data);
				// Remove current node
				q.dequeue();
				// Get new head
				node = q.peek();
			}
		}
		else
		{
			println("Empty Tree");
		}
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		// Create new tree
		var tree: BinaryTree = new BinaryTree();
		/*
		  Make A Binary Tree
		  -----------------------
		         1
		       /   \
		      2     3
		     /     / \
		    4     5   6
		   /     / \
		  7     8   9
		*/
		// Adding tree nodes
		tree.root = new TreeNode(1);
		tree.root.left = new TreeNode(2);
		tree.root.right = new TreeNode(3);
		tree.root.right.right = new TreeNode(6);
		tree.root.right.left = new TreeNode(5);
		tree.root.left.left = new TreeNode(4);
		tree.root.left.left.left = new TreeNode(7);
		tree.root.right.left.left = new TreeNode(8);
		tree.root.right.left.right = new TreeNode(9);
		// Display level order  element
		tree.levelOrder();
	}
}

Output

  1  2  3  4  5  6  7  8  9