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How to check string is alphanumeric or not using Regular Expression
  • Last Updated : 15 Oct, 2020

Given string str, the task is to check whether the string is alphanumeric or not by using Regular Expression

An alphanumeric string is a string that contains only alphabets from a-z, A-Z and some numbers from 0-9.

Examples: 

Input: str = “GeeksforGeeks123” 
Output: true 
Explanation: 
This string contains all the alphabets from a-z, A-Z, and the number from 0-9. Therefore, it is an alphanumeric string.
Input: str = “GeeksforGeeks” 
Output: false 
Explanation: 
This string contains all the alphabets from a-z, A-Z, but doesn’t contain any number from 0-9. Therefore, it is not an alphanumeric string.
Input: str = “GeeksforGeeks123@#” 
Output: false 
Explanation: 
This string contains all the alphabets from a-z, A-Z, and the number from 0-9 along with some special symbols. Therefore, it is not an alphanumeric string. 
 

Approach: This problem can be solved by using Regular Expression. 

  • Get the string.
  • Create a regular expression to check string is alphanumeric or not as mentioned below: 
regex = "^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+$";
  • Where: 
    • ^ represents the starting of the string
    • (?=.*[a-zA-Z]) represents the alphabets from a-z, A-Z
    • (?=.*[0-9]) represents any number from 0-9
    • [A-Za-z0-9] represents whether everything is either alphabetical or digit
    • + represents one or more times
    • $ represents the ending of the string
  • Match the given string with the regex, in Java, this can be done by using Pattern.matcher()
  • Return true if the string matches with the given regex, else return false

Below is the implementation of the above approach.
 

Java




// Java program to check string is
// alphanumeric or not using Regular Expression.
 
import java.util.regex.*;
 
class GFG {
 
    // Function to check string is alphanumeric or not
    public static boolean isAlphaNumeric(String str)
    {
        // Regex to check string is alphanumeric or not.
        String regex = "^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+$";
 
        // Compile the ReGex
        Pattern p = Pattern.compile(regex);
 
        // If the string is empty
        // return false
        if (str == null) {
            return false;
        }
 
        // Pattern class contains matcher() method
        // to find matching between given string
        // and regular expression.
        Matcher m = p.matcher(str);
 
        // Return if the string
        // matched the ReGex
        return m.matches();
    }
 
    // Driver Code.
    public static void main(String args[])
    {
 
        // Test Case 1:
        String str1 = "GeeksforGeeks123";
        System.out.println(
            str1 + ": "
            + isAlphaNumeric(str1));
 
        // Test Case 2:
        String str2 = "GeeksforGeeks";
        System.out.println(
            str2 + ": "
            + isAlphaNumeric(str2));
 
        // Test Case 3:
        String str3 = "GeeksforGeeks123@#";
        System.out.println(
            str3 + ": "
            + isAlphaNumeric(str3));
 
        // Test Case 4:
        String str4 = "123";
        System.out.println(
            str4 + ": "
            + isAlphaNumeric(str4));
 
        // Test Case 5:
        String str5 = "@#";
        System.out.println(
            str5 + ": "
            + isAlphaNumeric(str5));
    }
}

Python3




# Python3 program to check
# string is alphanumeric or
# not using Regular Expression.
import re
 
# Function to check string
# is alphanumeric or not
def isAlphaNumeric(str):
 
    # Regex to check string is
    # alphanumeric or not.
    regex = "^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+$"
 
    # Compile the ReGex
    p = re.compile(regex)
 
    # If the string is empty
    # return false
    if(str == None):
        return False
 
    # Return if the string
    # matched the ReGex
    if(re.search(p, str)):
        return True
    else:
        return False
 
# Driver Code
 
# Test Case 1:
str1 = "GeeksforGeeks123"
print(str1, ":",
      isAlphaNumeric(str1))
 
# Test Case 2:
str2 = "GeeksforGeeks"
print(str2, ":",
      isAlphaNumeric(str2))
 
# Test Case 3:
str3 = "GeeksforGeeks123@#"
print(str3, ":",
      isAlphaNumeric(str3))
 
# Test Case 4:
str4 = "123"
print(str4, ":",
      isAlphaNumeric(str4))
 
# Test Case 5:
str5 = "@#"
print(str5, ":",
      isAlphaNumeric(str5))
 
# This code is contributed by avanitrachhadiya2155
Output: 
GeeksforGeeks123: true
GeeksforGeeks: false
GeeksforGeeks123@#: false
123: false
@#: false


 




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