Interchange the diagonal of a matrix in scala

Scala program for Interchange the diagonal of a matrix. Here mentioned other language solution.

/*
  Scala program for
  Swap diagonal elements of matrix using recursion
*/
class Exchange()
{
	// Method which are perform swap operation
	// Here x and y indicate start and end rows
	// p and q indicates start and end columns
	def swapDiagonal(matrix: Array[Array[Int]], 
      x: Int, y: Int, p: Int, q: Int): Unit = {
		if (x >= y || p >= q)
		{
			return;
		}
		var temp: Int = matrix(x)(p);
		// Swap the element value
		matrix(x)(p) = matrix(x)(q);
		matrix(x)(q) = temp;
		temp = matrix(y)(p);
		// Swap the element value
		matrix(y)(p) = matrix(y)(q);
		matrix(y)(q) = temp;
		swapDiagonal(matrix, x + 1, y - 1, p + 1, q - 1);
	}
	// Display matrix elements
	def showMatrix(matrix: Array[Array[Int]], size: Int): Unit = {
		var i: Int = 0;
		// iterate rows
		while (i < size)
		{
			var j: Int = 0;
			// iterate columns
			while (j < size)
			{
				// Display element value
				print("  " + matrix(i)(j));
				j += 1;
			}
			//  include new line
			println();
			i += 1;
		}
		// include new line
		println();
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		// Define matrix element
		var matrix: Array[Array[Int]] = Array(
          Array(1, 2, 3, 4), 
          Array(5, 6, 7, 8), 
          Array(9, 10, 11, 12), 
          Array(13, 14, 15, 16)
        );
		// Assume N X N matrix
		var n: Int = matrix.length;
  		var task = new Exchange();
		// Display element
		task.showMatrix(matrix, n);
		// interchange request
		task.swapDiagonal(matrix, 0, n - 1, 0, n - 1);
		// Display element
		task.showMatrix(matrix, n);
	}
}

Output

  1  2  3  4
  5  6  7  8
  9  10  11  12
  13  14  15  16

  4  2  3  1
  5  7  6  8
  9  11  10  12
  16  14  15  13