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?

Try this: /^[a-z0-9]+$/i Check [here][1] too [1]: stackoverflow.com/questions/388996/… — Vimalnath
– Vimalnath, Commented Jun 28, 2012 at 9:34

caffreyd · Accepted Answer · 2019-03-06 01:43:47Z

93

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

edited Mar 6, 2019 at 1:43

caffreyd

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answered Jun 28, 2012 at 9:38

Raghav

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6 Comments

tster Over a year ago

-1 as this doesn't cover all alphanumberic characters. M42's response is better.

Fr4nz Over a year ago

Poor use of if, better would be return s.matches(pattern)

Adnan Abdollah Zaki Over a year ago

* allow empty string , use + , like this : ^[a-zA-Z0-9]+$

krick Over a year ago

Do you really need to add the boundary matchers (^,$) at the beginning and end? It seems like String pattern="[a-zA-Z0-9]+"; would behave the same way since + is greedy.

shiva Over a year ago

Need regex to check if string not contain "test" and contain only alphabet and space. please help

|

Toto · Accepted Answer · 2012-06-28 11:48:11Z

30

In order to be unicode compatible:

^[\pL\pN]+$

where

\pL stands for any letter
\pN stands for any number

answered Jun 28, 2012 at 11:48

Toto

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5 Comments

Abdalrahman Shatou Over a year ago

Not working. Giving: java.util.regex.PatternSyntaxException: Incorrect Unicode property near index 5.

Erk Over a year ago

IntelliJ also suggests \\p{Alnum} (but that's in Java 13)

slugmandrew Over a year ago

@Erk I believe that has been around since Java 7: docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html

Erk Over a year ago

@slugmandrew, good to know. I was hedging. Seems there is one as far back as java 6. But not java 5—it doesn't even seem to have a Pattern class.

devdanke Over a year ago

Works in Java May 2023. It's the most concise answer, yet still readable. (IntelliJ doesn't suggest change.)

Johannes Jander · Accepted Answer · 2016-03-18 08:38:02Z

18

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.

answered Mar 18, 2016 at 8:38

Johannes Jander

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Comments

ewan.chalmers · Accepted Answer · 2012-06-28 09:43:30Z

11

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}]+$".

edited Jun 28, 2012 at 9:43

answered Jun 28, 2012 at 9:36

ewan.chalmers

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Comments

Igor Chubin · Accepted Answer · 2012-06-28 09:33:36Z

5

Use character classes:

^[[:alnum:]]*$

answered Jun 28, 2012 at 9:33

Igor Chubin

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1 Comment

Mark A. Fitzgerald Over a year ago

This is the right idea, but POSIX character class syntax is not valid in Java, and the question is tagged as Java. The equivalent Java syntax for your answer is "^[\\p{Alnum}]*$", as mentioned below. (If such tagging is not considered to be sufficiently conspicuous by site guidelines, let me know and I'll add a comment to the question itself. :))

Seth Malaki · Accepted Answer · 2012-06-28 09:39:52Z

4

Pattern pattern = Pattern.compile("^[a-zA-Z0-9]*$");
Matcher matcher = pattern.matcher("Teststring123");
if(matcher.matches()) {
     // yay! alphanumeric!
}

answered Jun 28, 2012 at 9:39

Seth Malaki

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1 Comment

Gaurav Over a year ago

works flawlessly!

Dheeresh Singh · Accepted Answer · 2012-06-28 09:51:47Z

1

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()) {

}

edited Jun 28, 2012 at 9:51

answered Jun 28, 2012 at 9:39

Dheeresh Singh

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Comments

Unmitigated · Accepted Answer · 2021-05-11 20:41:43Z

1

To consider all Unicode letters and digits, Character.isLetterOrDigit can be used. In Java 8, this can be combined with String#codePoints and IntStream#allMatch.

boolean alphanumeric = str.codePoints().allMatch(Character::isLetterOrDigit);

answered May 11, 2021 at 20:41

Unmitigated

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Comments

Curtis Yallop · Accepted Answer · 2021-07-19 21:54:49Z

1

To include [a-zA-Z0-9_], you can use \w.

So myString.matches("\\w*"). (.matches must match the entire string so ^\\w*$ is not needed. .find can match a substring)

https://docs.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html

answered Jul 19, 2021 at 21:54

Curtis Yallop

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Comments

Emma Marcier · Accepted Answer · 2019-04-16 20:58:01Z

-1

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...
}

edited Apr 16, 2019 at 20:58

Emma Marcier

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answered Apr 16, 2019 at 15:30

BrianG7

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Comments

Emma Marcier · Accepted Answer · 2019-04-16 21:26:06Z

-1

100% alphanumeric RegEx (it contains only alphanumeric, not even integers & characters, only alphanumeric)

For example:

special char (not allowed)
123 (not allowed)
asdf (not allowed)
1235asdf (allowed)

String name="^[^<a-zA-Z>]\\d*[a-zA-Z][a-zA-Z\\d]*$";

edited Apr 16, 2019 at 21:26

Emma Marcier

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answered Aug 31, 2016 at 13:32

Amit

9

1 Comment

Ayush Over a year ago

so a12 is not alphanumeric ?

Justin Cairns · Accepted Answer · 2019-03-18 20:03:32Z

-4

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;
    }

answered Mar 18, 2019 at 20:03

Justin Cairns

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