Introduction

In this demo I have used NetBeans IDE 8.2 for debugging purpose. But you can use any java programming language compiler as per your availability..

import java.util.Scanner;
public class JavaExcercise {
 
 
  public static void main(String[] args)
    {
        Scanner in = new Scanner(System.in);
 
        System.out.print("Enter any alphabet: ");
        String input = in.next().toLowerCase();
 
        boolean uppercase = input.charAt(0) >= 65 && input.charAt(0) <= 90;
        boolean lowercase = input.charAt(0) >= 97 && input.charAt(0) <= 122;
        boolean vowels = input.equals("a") || input.equals("e") || input.equals("i")
                || input.equals("o") || input.equals("u");
 
        if (input.length() > 1)
        {
            System.out.println("Error. Not a single character.");
        }
        else if (!(uppercase || lowercase))
        {
            System.out.println("Error. Not a letter. Enter uppercase or lowercase letter.");
        }
        else if (vowels)
        {
            System.out.println("Input letter is Vowel");
        }
        else
        {
            System.out.println("Input letter is Consonant");
        }
    }
}

Result