Regex for checking if a string is strictly alphanumeric

Question

How can I check if a string contains only numbers and alphabets ie. is alphanumeric?

Answer 1

Considering you want to check for ASCII Alphanumeric characters, Try this: "^[a-zA-Z0-9]*$". Use this RegEx in String.matches(Regex), it will return true if the string is alphanumeric, else it will return false.

public boolean isAlphaNumeric(String s){
    String pattern= "^[a-zA-Z0-9]*$";
    return s.matches(pattern);
}

If it will help, read this for more details about regex: http://www.vogella.com/articles/JavaRegularExpressions/article.html

Answer 2

See the documentation of Pattern.

Assuming US-ASCII alphabet (a-z, A-Z), you could use \p{Alnum}.

A regex to check that a line contains only such characters is "^[\\p{Alnum}]*$".

That also matches empty string. To exclude empty string: "^[\\p{Alnum}]+$".

Answer 3

If you want to include foreign language letters as well, you can try:

String string = "hippopotamus";
if (string.matches("^[\\p{L}0-9']+$")){
    string is alphanumeric do something here...
}

Or if you wanted to allow a specific special character, but not any others. For example for # or space, you can try:

String string = "#somehashtag";
if(string.matches("^[\\p{L}0-9'#]+$")){
    string is alphanumeric plus #, do something here...
}

Answer 4

try this [0-9a-zA-Z]+ for only alpha and num with one char at-least..

may need modification so test on it

http://www.regexplanet.com/advanced/java/index.html

Pattern pattern = Pattern.compile("^[0-9a-zA-Z]+$");
Matcher matcher = pattern.matcher(phoneNumber);
if (matcher.matches()) {

}

Answer 5

To check if a String is alphanumeric, you can use a method that goes through every character in the string and checks if it is alphanumeric.

    public static boolean isAlphaNumeric(String s){
            for(int i = 0; i < s.length(); i++){
                    char c = s.charAt(i);
                    if(!Character.isDigit(c) && !Character.isLetter(c))
                            return false;
            }
            return true;
    }

Answer 6

It's 2016 or later and things have progressed. This matches Unicode alphanumeric strings:

^[\\p{IsAlphabetic}\\p{IsDigit}]+$

See the reference (section "Classes for Unicode scripts, blocks, categories and binary properties"). There's also this answer that I found helpful.