Regular Expression Android

Question

I am trying to check if an at character only exist in an android edit-view. I am new to regular expression and i implemented the forthcoming code. where am i mistaken ? Here is my code

try {

        Pattern pattern = Pattern.compile("/@");
        Matcher matcher = pattern.matcher(valEmail);

        if (!matcher.matches()) {

            Toast.makeText(this," Invid no @ character ",Toast.LENGTH_LONG).show();

        }

    }catch(Exception ex){}

for which do you have write Regular Expression ,i think you want for Email? — Herry
– Herry, Commented Apr 25, 2012 at 6:12
i would like to check if only one @ character present in an email address using regular expression — user1355385
– user1355385, Commented Apr 25, 2012 at 6:15
You may want to look at this site for pattern for email validation. The problem with your code is that you don't need the "/" before the "@" — Rajesh
– Rajesh, Commented Apr 25, 2012 at 6:16
Thank you for the site explanation. It helps a lot and you're right dude — user1355385
– user1355385, Commented Apr 25, 2012 at 6:26

Jon Skeet · Accepted Answer · 2012-04-25 06:20:34Z

6

There are two problems with your current code:

The leading slash means it really is looking for "/@" rather than just "@". You seem to think that "/" does something special within a regex - it doesn't.
You're using matches() which tries to match the whole of the input; you want find which will just try to find a match for the regex somewhere in the input.

Why are you using regular expressions at all though? Why not just:

if (!valEmail.contains("@")) {
    ...
}

That will check whether the address contains any "@" signs. If you want to check that there's only one "@" sign, you could use:

int atIndex = valEmail.indexOf('@');
if (atIndex == -1) {
    // Handling for *no* @ sign
}
if (valEmail.indexOf('@', atIndex + 1) != -1) {
    // Handling for multiple @ signs
}

If you do want to use regular expressions, there are rather more sophisticated email address validation regular expressions available. (There lots of different ones with different levels of validity - make sure you get one designed for the Java flavour of regex.) I wouldn't use one just for this though - only use regular expressions where you're really interested in pattern matching.

If you want to use a regex for "at least one non-@, following by @, followed by at least one non-@" you could use:

// TODO: Compile this once and reuse
Pattern pattern = Pattern.compile("[^@]+@[^@]+");
Matcher matcher = pattern.matcher(valEmail);

if (!matcher.matches()) {
    ...
}

As an aside, this:

catch(Exception ex){}

is never a good idea. Please don't just ignore errors indiscriminately.

edited Apr 25, 2012 at 6:20

answered Apr 25, 2012 at 6:13

Jon Skeet

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2 Comments

StilesCrisis Over a year ago

Your code is very short, and very incorrect. Get it right first. I also wouldn't consider regexes to be a pinnacle of performance.

Jon Skeet Over a year ago

@user1355385: Compiling a regular expression and then using it is not going to be faster (or shorter) than text.contains("@"). And as StilesCrisis says - get your code working first before you worry about performance.

Herry · Accepted Answer · 2012-04-25 06:16:00Z

2

For Email you can use Below Regular Expression .

 private static final String EMAIL_PATTERN = "^[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$";



    try {

    Pattern pattern = Pattern.compile(EMAIL_PATTERN);
    Matcher matcher = pattern.matcher(valEmail);

    if (!matcher.matches()) {

        Toast.makeText(this," Invid no @ character ",Toast.LENGTH_LONG).show();

    }

}catch(Exception ex){
}

answered Apr 25, 2012 at 6:16

Herry

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Comments

shift66 · Accepted Answer · 2012-04-25 06:15:01Z

1

matches() method checks if whole string matches to regular expression. You should use find() method instead of matches.And / character shouldn't be there.
But instead of all this you better use contains() method of string. if(valEmail.contains("@"))

answered Apr 25, 2012 at 6:15

shift66

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Comments

StilesCrisis · Accepted Answer · 2012-04-25 06:22:17Z

1

You have a leading / in the regular expression that shouldn't be there.

Additionally, you should be using find, not matches.

edited Apr 25, 2012 at 6:22

answered Apr 25, 2012 at 6:12

StilesCrisis

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2 Comments

user1355385 Over a year ago

this / intend to check if only one @ character present. Why should i remove it ?

Jon Skeet Over a year ago

@user1355385: Why do you think it will do that?

Dheeraj Joshi · Accepted Answer · 2012-04-25 06:14:31Z

0

Just use @ without a / in the beginning.

answered Apr 25, 2012 at 6:14

Dheeraj Joshi

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