How to determine if a String has non-alphanumeric characters?

Question

I need a method that can tell me if a String has non alphanumeric characters.

For example if the String is "abcdef?" or "abcdefà", the method must return true.

http://stackoverflow.com/questions/1795402/java-check-a-string-if-there-is-a-special-character-in-it — Wojciech Owczarczyk, Nov 23 '11 at 19:56
http://stackoverflow.com/questions/11241690/regex-for-checking-if-a-string-is-strictly-alphanumeric — treecoder, May 02 '14 at 02:15

Fabian Barney · Accepted Answer · 2011-11-23T20:39:03.337

161

Using Apache Commons Lang:

!StringUtils.isAlphanumeric(String)

Alternativly iterate over String's characters and check with:

!Character.isLetterOrDigit(char)

You've still one problem left: Your example string "abcdefà" is alphanumeric, since à is a letter. But I think you want it to be considered non-alphanumeric, right?!

So you may want to use regular expression instead:

String s = "abcdefà";
Pattern p = Pattern.compile("[^a-zA-Z0-9]");
boolean hasSpecialChar = p.matcher(s).find();

edited Nov 23 '11 at 20:39

answered Nov 23 '11 at 20:00

Fabian Barney

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7

I would like to avoid importing external libraries if not strictly necessary. And yes: I want à to be considered as non alphanumeric. – lugeno Nov 23 '11 at 21:19
a *side note:* unrelated but just to remind ```StringUtils.isAlphaNumeric("abc");``` returns ```true``` if the str contains only alphabets. – Brooklyn99 Jan 25 '21 at 02:50

loscuropresagio · Answer 2 · 2011-11-23T20:40:07.787

29

One approach is to do that using the String class itself. Let's say that your string is something like that:

String s = "some text";
boolean hasNonAlpha = s.matches("^.*[^a-zA-Z0-9 ].*$");

one other is to use an external library, such as Apache commons:

String s = "some text";
boolean hasNonAlpha = !StringUtils.isAlphanumeric(s);

edited Nov 23 '11 at 20:40

answered Nov 23 '11 at 20:03

loscuropresagio

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+1: regex is here the winner I think since the OP does not really want to check for alphanumeric characters. He wants sth. like `hasSpecialCharacters(String)` with his own definition of "special". – Fabian Barney Nov 23 '11 at 20:08
2

That won't quite work: `String.matches(...)` in Java checks if the regex matches the *whole* string. – ruakh Nov 23 '11 at 20:20
`boolean hasNonAlpha = ! … ^[A-Za-z0-9 ]*$` – Isaak Osipovich Dunayevsky Jun 01 '18 at 06:49

score 6 · Answer 3 · answered Nov 23 '11 at 19:57

6

You have to go through each character in the String and check Character.isDigit(char); or Character.isletter(char);

Alternatively, you can use regex.

answered Nov 23 '11 at 19:57

Mechkov

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For example, "-1234" is a number, not an alphanumeric string. But your logic Character.isDigit will return false for "-". :( – Abhishek Aug 06 '14 at 11:52
I think it is Character.isLetter not Character.isletter – InterLinked Jul 14 '18 at 17:50

score 4 · Answer 4 · answered Oct 22 '17 at 14:15

Use this function to check if a string is alphanumeric:

public boolean isAlphanumeric(String str)
{
    char[] charArray = str.toCharArray();
    for(char c:charArray)
    {
        if (!Character.isLetterOrDigit(c))
            return false;
    }
    return true;
}

It saves having to import external libraries and the code can easily be modified should you later wish to perform different validation checks on strings.

score 2 · Answer 5 · edited Jul 20 '15 at 13:29

2

If you can use the Apache Commons library, then Commons-Lang StringUtils has a method called isAlphanumeric() that does what you're looking for.

edited Jul 20 '15 at 13:29

erip

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answered Nov 23 '11 at 20:00

Shaun

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score 1 · Answer 6 · answered Jul 21 '15 at 20:18

1

string.matches("^\\W*$"); should do what you want, but it does not include whitespace. string.matches("^(?:\\W|\\s)*$"); does match whitespace as well.

answered Jul 21 '15 at 20:18

nike4613

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score 0 · Answer 7 · answered Jul 18 '17 at 21:12

You can use isLetter(char c) static method of Character class in Java.lang .

public boolean isAlpha(String s) {
    char[] charArr = s.toCharArray();

    for(char c : charArr) {
        if(!Character.isLetter(c)) {
            return false;
        }
    }
    return true;
}

score 0 · Answer 8 · answered Jul 17 '20 at 07:07

0

Though it won't work for numbers, you can check if the lowercase and uppercase values are same or not, For non-alphabetic characters they will be same, You should check for number before this for better usability

answered Jul 17 '20 at 07:07

Abhishek Choudhary

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How to determine if a String has non-alphanumeric characters?

8 Answers8

Linked

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