Java - regex not working

Question

I have a string of "abc123(" and want to check if contains one or more chars that are not a number or character.

"abc123(".matches("[^a-zA-Z0-9]+"); should return true in this case? But it dose not! Whats wrong?

My test script:

public class NewClass {
    public static void main(String[] args) {
        if ("abc123(".matches("[^a-zA-Z0-9]+")) {
            System.out.println("true");
        }
    }
}

On a point of purely REGEX grammar, it seems fine (I don't know Java, though.) Returns true in JavaScript. Definitely returns false? — Mitya
– Mitya, Commented Jul 13, 2012 at 13:54
matches, in Java, means "matches the whole string". In your case, the '(' at the end is the only part matching "a sequence of one-or-more chars that is not alphanumeric"... — tucuxi
– tucuxi, Commented Jul 13, 2012 at 14:00
Yup.. matches(yourRegex) in Java really means matches("^" + yourRegex + "$") — Alderath
– Alderath, Commented Jul 13, 2012 at 14:12

unholysampler · Accepted Answer · 2012-07-13 14:22:08Z

5

In Java, the expressions has to match the entire string, not just part of it.

myString.matches("regex") returns true or false depending whether the string can be matched entirely by the regular expression. It is important to remember that String.matches() only returns true if the entire string can be matched. In other words: "regex" is applied as if you had written "^regex$" with start and end of string anchors. Source

Your expression is looking for part of the string, not the whole thing. You can change your expression to .*YOUR_EXPRESSION.* and it will expand to match the entire string.

edited Jul 13, 2012 at 14:22

answered Jul 13, 2012 at 14:00

unholysampler

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4 Comments

wowpatrick Over a year ago

And how can I fix this? I want to now if it contains it, regardless of the rest!

unholysampler Over a year ago

@wowpatrick: You can add .* to the start and end of you existing expressions.

wowpatrick Over a year ago

Hey yeah that work! Could you add it to the answer? Than were don here :)

wowpatrick Over a year ago

Great, thanks! Works fine now and got a better understanding of Javas regex.

EEP · Accepted Answer · 2012-07-13 13:57:18Z

4

Rather than checking to see if it contains only letters and numbers, why not check to see if it contains anything other than that? You can use the not word group (\W) and if that returns true than you know the string contains something other than the characters you are looking for,

"abc123(".matches("[\W]");

If this returns true than there is something other than just word characters and digits.

answered Jul 13, 2012 at 13:57

EEP

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Comments

Roman · Accepted Answer · 2012-07-13 19:13:12Z

2

Expression [^A-Za-z0-9]+ means 'not letters or digits'. You probably want to replace it with ^[A-Za-z0-9]+$ which means 'Only letters or digits'.

edited Jul 13, 2012 at 19:13

answered Jul 13, 2012 at 13:57

Roman

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1 Comment

m0skit0 Over a year ago

That regex you're proposing will match one character string only. Add a +: ^[A-Za-z0-9]+$

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