implement stack using linked list in kotlin

Kotlin program for implement stack using linked list. Here problem description and other solutions.

// Kotlin program for
// Implementation stack using linked list

// Stack Node
class StackNode
{
	var data: Int;
	var next: StackNode ? ;
	constructor(data: Int, top: StackNode ? )
	{
		this.data = data;
		this.next = top;
	}
}
class MyStack
{
	var top: StackNode ? ;
	var count: Int;
	constructor()
	{
		this.top = null;
		this.count = 0;
	}
	// Returns the number of element in stack
	fun size(): Int
	{
		return this.count;
	}
	fun isEmpty(): Boolean
	{
		if (this.size() > 0)
		{
			return false;
		}
		else
		{
			return true;
		}
	}
	// Add a new element in stack
	fun push(data: Int): Unit
	{
		// Make a new stack node
		// And set as top
		this.top = StackNode(data, this.top);
		// Increase node value
		this.count += 1;
	}
	// Add a top element in stack
	fun pop(): Int
	{
		var temp: Int = 0;
		if (this.isEmpty() == false)
		{
			// Get remove top value
			temp = this.top!!.data;
			this.top = this.top?.next;
			// Reduce size
			this.count -= 1;
		}
		return temp;
	}
	// Used to get top element of stack
	fun peek(): Int
	{
		if (!this.isEmpty())
		{
			return this.top!!.data;
		}
		else
		{
			return 0;
		}
	}
}
class Test
{}
fun main(args: Array < String > ): Unit
{
	// Create new stack 
	val s: MyStack = MyStack();
	println("\n Is empty : " + s.isEmpty());
	// Add element
	s.push(15);
	s.push(14);
	s.push(31);
	s.push(21);
	s.push(10);
	println("\n Top  : " + s.peek());
	println(" Size : " + s.size());
	println("\n Is empty : " + s.isEmpty());
	// Delete Stack Element
	var data: Int = s.pop();
	println("\n Pop element " + data);
	println(" Size : " + s.size());
	data = s.pop();
	println("\n Pop element " + data);
	println(" Size : " + s.size());
}

Output

 Is empty : true

 Top  : 10
 Size : 5

 Is empty : false

 Pop element 10
 Size : 4

 Pop element 21
 Size : 3