当用户输入数字而不是字符串时显示错误

Question

I've tried to find something on this but have not seen anything related in the past hour of searching. I am looking to throw an error when the user tries to enter a number instead of a String.

I've found more than enough resources on how to throw and error when the user enters a string instead of a int, but nothing about the other way.

I'll just make up some code real quick

import java.util.Scanner;

public class ayylmao {

    public static void main(String[] args) {
            Scanner scan = new Scanner(System.in);
            System.out.println("Enter your first name");
            String AyyLmao = scan.nextLine();
            System.out.println("Your first name is " + AyyLmao);
/*
Want it to say something like "Error: First character must be from the alphabet!" if the user tries to enter a number.
*/

        }
    }

Answer 1

Try this:

public static boolean isIntegerParseInt(String str) {
    try {
        Integer.parseInt(str);
        return true;
    } catch (NumberFormatException nfe) {}
    return false;
}

Answer 2

If it's only the first character you're interested in, you could use a test like this:

if (AyyLmao.charAt(0) >= '0' && AyyLmao.charAt(0) <= '9'){
  /* complain here */
}

A test on the whole string, as you apparently have found out already, would be:

try{
  Integer.parseInt(AyyLmao);
  /* complain here */
} catch(NumberFormatException ex){
  /* this would be OK in your case */
}

Answer 3

Use the regular expression "^\\\\d" to find out if there are any digits at the start of your string.

For example, in order to check if the start of a name is a digit:

String regex = "^\\d";
Pattern p = Pattern.compile(regex);
Matcher m = p.matcher(yourInput);
if(m.find()) {
   // Your input starts with a digit
}

Here is a good place to get started on regular expressions: http://www.vogella.com/tutorials/JavaRegularExpressions/article.html

Answer 4

private static String acceptName() {
        // TODO Auto-generated method stub
        Boolean flag = Boolean.TRUE;
        String name = "";
        while (flag) {
            Scanner scan = new Scanner(System.in);
            System.out.println("enter name : ");
            name = scan.nextLine();
            try {
                Integer no = Integer.parseInt(name);
                System.out.println("you have entered number....");
            } catch (NumberFormatException e) {
                flag = Boolean.FALSE;

            }
        }
        return name;

    }