如何修改我的代码以只接受某种数据类型？

Question

What can I do to modify this, is there any java function for that? What needs to be done so that it only accepts characters and returns an error message for other data types?

import java.util.*;
    public class problem5
    {
      public static void main(String[] args)
      {
        Scanner in = new Scanner(System.in);
        System.out.print("Enter a letter from the alphabet: ");
        char letter = in.next(".").charAt(0);
        char vowels[] = {'A','E','I','O','U','a','e','i','o','u'};
        int vowelcount = 0;
        for (int i = 0; i < 10; i++)
        {
          if (vowels[i] == letter)
          {
            vowelcount++;
          }
        }
        if (vowelcount > 0)
        {
          System.out.println("You entered a vowel.");
        }
        else
        {
          System.out.println("You entered a consonant.");
        }
      }
    }

Answer 1

I need to reject input that has more than 1 char – Nico Dela Cruz

You just need to check the length of your input

String input = in.next(".");
if(input.length == 1){
    char letter = input.charAt(0);
    ...
}

Add an else if you want to add an error message of some sort.

To check the input to only accept letter , you have Character.isLetter(char) to check every "letter" in UNICODE for you.

If you want to only accept a range of az and/or AZ , you can do it yourself with an if condition or using regex.

Answer 2

Wrap your loop in a statement such as:

if (Character.isLetter(letter)){

and put and else clause at the end for your error

Edit:

OP has changed their question slightly, so you can either:

-Accept only the first character entered:

char letter = in.next().trim().charAt(0);

-Or as AxelH said above, only proceed if user enters one char:

if(input.length == 1){
    char letter = input.charAt(0);