Find the frequency of each element in an array in kotlin

Kotlin program for Find the frequency of each element in an array. Here problem description and other solutions.

/*
  Kotlin program
  Count frequency of each element in array 
*/
class Occurrence
{
	// Function which is display array elements
	fun display(arr: Array < Int > ): Unit
	{
		var i: Int = 0;
		while (i < arr.count())
		{
			print("  " + arr[i]);
			i += 1;
		}
		print("\n");
	}
	// Count occurrence of given array
	fun frequency(arr: Array < Int > ): Unit
	{
		// Display given array
		this.display(arr);
		// Create a empty map
		var map: HashMap < Int, Int > = HashMap < Int, Int > ();
		var i: Int = 0;
		while (i < arr.count())
		{
			if (map.containsKey(arr[i]))
			{
				// When key exists then update value
				map.put(arr[i], map.getValue(arr[i]) + 1);
			}
			else
			{
				// Add new element
				map.put(arr[i], 1);
			}
			i += 1;
		}
		println("  Occurrence ");
		//  Display calculated result
		for ((key, value) in map)
		{
			println("  " + key + "  :  " + value);
		}
	}
}
fun main(args: Array < String > ): Unit
{
  	val task: Occurrence = Occurrence();
	// Array element
	val arr: Array < Int > = arrayOf(1, 3, 2, 1, 4, 2, 7, 9, 1, 3, 3, 4, 7);
	task.frequency(arr);
}

Output

  1  3  2  1  4  2  7  9  1  3  3  4  7
  Occurrence
  1  :  3
  2  :  2
  3  :  3
  4  :  2
  7  :  2
  9  :  1