Java: Match a string that contains only upper and lowercase letters, numbers, and underscores

Last update on May 24 2025 12:59:38 (UTC/GMT +8 hours)

8. Match Alphanumeric Underscore

Write a Java program to match a string containing only upper and lowercase letters, numbers, and underscores.

Sample Solution:

Java Code:

import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class test {
 
   public static void main(String[] args) {
	   
	    System.out.println(validate("The quick brown fox jumps over the lazy dog."));
	    System.out.println(validate("Java_Exercises_1"));
	    System.out.println(validate("Java_Exercises_11.0"));
	    System.out.println(validate("w3r"));
        }

   public static String validate(String text) {
	    Pattern pattern = Pattern.compile("^[a-zA-Z0-9_]*$");
		 Matcher m = pattern.matcher(text);
		
	   if (m.find())
                return "Found a match!";
       else
                return "Not matched!";
   }
}

Sample Output:

Not matched!
Found a match!
Not matched!
Found a match!

Pictorial Presentation:

Flowchart :

For more Practice: Solve these Related Problems:

• Write a Java program to verify that a string contains only letters, digits, and underscores using a regular expression.
• Write a Java program to implement a method that returns true if a string is alphanumeric with underscores and false otherwise.
• Write a Java program to test various strings against a pattern that allows only upper/lowercase letters, numbers, and underscores.
• Write a Java program to remove any characters from a string that are not letters, digits, or underscores.

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