Java Coding Help! Can't get if statement to confirm string

Write a program that prompts the user to provide a single character from the alphabet. Print Vowel or Consonant, depending on the user input. If the user input is not a letter (between a and z or A and Z), or is a string of length > 1, print an error message.

I have been trying to solve this problem, and basically have it all figured out but have ran into two issues. How do I get the scanner to recognize an error if the user inputs a number rather than a letter. Also how would one not have to repeat their input. Is there a way to have the first if statement evaluate if the user entered a string?

import java.util.*;

public class MessAround {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		System.out.println("Please Provide single character from the alphabet: ");
        String letter = scan.next();
        
        if (scan.hasNext())
        {
            letter = letter.toLowerCase();
            if (letter.equals("a") || letter.equals("e") || letter.equals("i") || letter.equals("o") || letter.equals("u"))
            {
                System.out.println("Vowel");
            }
            else if (letter.length() > 1)
            {
                System.out.println("Error");
            }
            else
            {
                System.out.println("Consonant");
            }
        }
        else
        {
            System.out.println("Error");
        }
	}

}

Add to your ifs: if (isNumber(letter)) { // A number was entered. and create a isNumber(String) method that returns true if the string is a number in the sense that you mean it.

Or better make it a String isValid(String) method and implement in the method your validation rules. It could return null if the validation is successful otherwise a message.

There are many ways to solve this. A couple of them are as follows:

Using Regex:

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);

		System.out.print("Please Provide single character from the alphabet: ");
		String letter = scan.next();

		if (!letter.matches("[A-Za-z]")) {
			System.out.println("Error");
		} else {
			letter = letter.toLowerCase();
			if (letter.matches("[aeiou]")) {
				System.out.println("Vowel");
			} else {
				System.out.println("Consonant");
			}
		}
	}
}

Learn about regex from here.

Using the class, Character:

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);

		System.out.print("Please Provide single character from the alphabet: ");
		String letter = scan.next();

		if (letter.length() == 1 && Character.isAlphabetic(letter.charAt(0))) {
			char ch = Character.toLowerCase(letter.charAt(0));
			if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
				System.out.println("Vowel");
			} else {
				System.out.println("Consonant");
			}
		} else {
			System.out.println("Error");
		}
	}
}