Java regex program to verify whether a String contains at least one alphanumeric character.

Following regular expression matches a string that contains at least one alphanumeric characters −

"^.*[a-zA-Z0-9]+.*$";

Where,

• ^.* Matches the string starting with zero or more (any) characters.

• [a-zA-Z0-9]+ Matches at least one alpha-numeric character.

• .*$ Matches the string ending with zero or more (ant) characters.

Example 1

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Example {
   public static void main(String args[]) {
      //Reading String from user
      System.out.println("Enter a string");
      Scanner sc = new Scanner(System.in);
      String input = sc.nextLine();
      //Regular expression
      String regex = "^.*[a-zA-Z0-9]+.*$";
      //Compiling the regular expression
      Pattern pattern = Pattern.compile(regex);
      //Retrieving the matcher object
      Matcher matcher = pattern.matcher(input);
      int count = 0;
      if(matcher.matches()) {
         System.out.println("Given string is valid");
      } else {
         System.out.println("Given string is not valid");
      }
   }
}

Output 1

Enter a string
###test123$$$
Given string is valid

Output 2

Enter a string
####$$$$
Given string is not valid

Example 2

import java.util.Scanner;
public class Example {
   public static void main(String args[]) {
      //Reading String from user
      System.out.println("Enter a string");
      Scanner sc = new Scanner(System.in);
      String input = sc.nextLine();
      //Regular expression
      String regex = "^.*[a-zA-Z0-9]+.*$";
      boolean result = input.matches(regex);
      if(result) {
         System.out.println("Valid match");
      }else {
         System.out.println("In valid match");
      }
   }
}

Output 1

Enter a string
###test123$$$
Valid match

Output 2

Enter a string
####$$$$
In valid match