Find the frequency of each element in an array in scala

Scala program for Find the frequency of each element in an array. Here more information.

import scala.collection.mutable._;
class Occurrence()
{
	// Function which is display array elements
	def display(arr: Array[Int]): Unit = {
		var i: Int = 0;
		while (i < arr.length)
		{
			print("   " + arr(i));
			i += 1;
		}
		print("\n");
	}
	// Count occurrence of given array
	def frequency(arr: Array[Int]): Unit = {
		// Display given array
		display(arr);
		// Create a empty map
		var map: HashMap[Int, Int] = new HashMap[Int, Int]();
		var i: Int = 0;
		while (i < arr.length)
		{
			if (map.contains(arr(i)))
			{
				// When key exists then update value
				map.addOne(arr(i), map.get(arr(i)).get + 1);
			}
			else
			{
				// Add new element
				map.addOne(arr(i), 1);
			}
			i += 1;
		}
		println("  Occurrence ");
		//  Display calculated result
		for ((key, value) <- map)
		{
			println("  " + key + "  :  " + value);
		}
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		// Array element
		var arr: Array[Int] = Array(1, 3, 2, 1, 4, 2, 7, 9, 1, 3, 3, 4, 7);
        var task: Occurrence = new Occurrence();
		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