How to check string is alphanumeric or not using Regular Expression

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
^ 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
Python3
// 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]+$";         // Compile the ReGex        Pattern p = Pattern.compile(regex);         // If the string is empty        // return false        if (str == null) {            return false;        }         // Pattern class contains matcher() method        // to find matching between given string        // and regular expression.        Matcher m = p.matcher(str);         // Return if the string        // matched the ReGex        return m.matches();    }     // Driver Code.    public static void main(String args[])    {         // Test Case 1:        String str1 = "GeeksforGeeks123";        System.out.println(            str1 + ": "            + isAlphaNumeric(str1));         // Test Case 2:        String str2 = "GeeksforGeeks";        System.out.println(            str2 + ": "            + isAlphaNumeric(str2));         // Test Case 3:        String str3 = "GeeksforGeeks123@#";        System.out.println(            str3 + ": "            + isAlphaNumeric(str3));         // Test Case 4:        String str4 = "123";        System.out.println(            str4 + ": "            + isAlphaNumeric(str4));         // Test Case 5:        String str5 = "@#";        System.out.println(            str5 + ": "            + isAlphaNumeric(str5));    }}
# Python3 program to check# string is alphanumeric or# not using Regular Expression.import re # Function to check string# is alphanumeric or notdef isAlphaNumeric(str):     # Regex to check string is    # alphanumeric or not.    regex = "^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+$"     # 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
GeeksforGeeks123: true
GeeksforGeeks: false
GeeksforGeeks123@#: false
123: false
@#: false



 
avanitrachhadiya2155
CPP-regex
java-regular-expression
Pattern Searching
Strings
Strings
Pattern Searching
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