How to check if a string is made only of letters and numbers

Question

Let's say a user inputs text. How does one check that the corresponding String is made up of only letters and numbers?

import java.util.Scanner;
public class StringValidation {
    public static void main(String[] args) {
       Scanner in = new Scanner(System.in);
       System.out.println("Enter your password");
       String name = in.nextLine();
       (inert here)

Answer 1

You can call matches function on the string object. Something like

str.matches("[a-zA-Z0-9]*")

This method will return true if the string only contains letters or numbers.

Tutorial on String.matches: http://www.tutorialspoint.com/java/java_string_matches.htm

Regex tester and explanation: https://regex101.com/r/kM7sB7/1

Answer 2

1. Use regular expressions :

   Pattern pattern = Pattern.compile("\\p{Alnum}+");
   Matcher matcher = pattern.matcher(name);
   if (!matcher.matches()) {
       // found invalid char
   }
   

2. for loop and no regular expressions :

   for (char c : name.toCharArray()) {
       if (!Character.isLetterOrDigit(c)) {
           // found invalid char
           break;
       }
   }
   

Both methods will match upper and lowercase letters and numbers but not negative or floating point numbers

Answer 3

Modify the Regular expression from [a-zA-Z0-9] to ^[a-zA-Z0-9]+$

String text="abcABC983";
System.out.println(text.matches("^[a-zA-Z0-9]+$"));

Current output: true

Answer 4

The regular expression character class \p{Alnum} can be used in conjunction with String#matches. It is equivalent to [\p{Alpha}\p{Digit}] or [a-zA-Z0-9].

boolean allLettersAndNumbers = str.matches("\\p{Alnum}*");
// Change * to + to not accept empty String

See the Pattern documentation.