Función CountDV Aprende programación con ejercicios Java

public class Main
{
	public static void CountDV(String answer, int amountOfDigits, int amountOfVowels)
	{
		amountOfDigits = 0;
		amountOfVowels = 0;

		for (int i = 0; i < answer.length(); i++)
		{
			switch (answer.substring(i, i + 1).toLowerCase())
			{
				case "a":
				case "e":
				case "i":
				case "o":
				case "u":
					amountOfVowels++;
					break;
				case "0":
				case "1":
				case "2":
				case "3":
				case "4":
				case "5":
				case "6":
				case "7":
				case "8":
				case "9":
					amountOfDigits++;
					break;
			}
		}
	}

	public static void main(String[] args)
	{
		int amountOfDigits = 0;
		int amountOfVowels = 0;

		CountDV("This", amountOfDigits, amountOfVowels);

		System.out.println(amountOfDigits);
		System.out.println(amountOfVowels);
	}
}