Java: Check whether a string contains only a certain set of characters (a-z, A-Z and 0-9)

Last update on May 24 2025 12:59:06 (UTC/GMT +8 hours)

1. Check Alphanumeric String

Write a Java program to check whether a string contains only a certain set of characters (in this case a-z, A-Z and 0-9).

Sample Solution:

Java Code:

import java.util.Scanner;
public class test {
 
   public static void main(String[] args) {
	   
	    System.out.println(validate("ABCDEFabcdef123450"));
		System.out.println(validate("SQL"));		
		System.out.println(validate("Java"));
		System.out.println(validate("*&%@#!}{"));
		System.out.println(validate("w3resource.com"));
        }

   public static boolean validate(String text) {
    return text.matches("^[\\w]+$");
  }
}

Sample Output:

true
true
true
false
false    

Pictorial Presentation:

Flowchart :

For more Practice: Solve these Related Problems:

• Write a Java program to validate that a string contains only alphanumeric characters using a predefined regex pattern.
• Write a Java program to verify that a string does not include any special characters by iterating over its characters.
• Write a Java program to implement a custom method that checks if every character in a string is within the ranges a–z, A–Z, or 0–9.
• Write a Java program to compare a regex-based validation with a manual character check for alphanumeric strings.

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