Count Vowels and Consonants in String

public class CountVowels {
    public static void main(String[] args) {
        String line = "This is a simple sentence";
        int vowels = 0, consonants = 0, digits = 0, spaces = 0;

        line = line.toLowerCase();
        for (int i = 0; i < line.length(); ++i) {
            char ch = line.charAt(i);

            if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
                ++vowels;
            } else if ((ch >= 'a' && ch <= 'z')) {
                ++consonants;
            } else if (ch >= '0' && ch <= '9') {
                ++digits;
            } else if (ch == ' ') {
                ++spaces;
            }
        }

        System.out.println("Vowels: " + vowels);
        System.out.println("Consonants: " + consonants);
        System.out.println("Digits: " + digits);
        System.out.println("White spaces: " + spaces);
    }
}