Should I really use REGEX or stay with dirty Java IF statements ? (For performance)

Question

Here is the code !

private boolean isIdCorrect(String userIdToAdd) {
    boolean checkValues = true;
    if(userIdToAdd.length() == 18) {
        if(userIdToAdd.charAt(0) == '#'
                && userIdToAdd.charAt(7) == '@') {
            for(int i = 1 ; i < 7 ; i++) {
                if(!((userIdToAdd.charAt(i) >= 'a'
                        && userIdToAdd.charAt(i) <= 'f')
                        || (userIdToAdd.charAt(i) >= '0'
                                && userIdToAdd.charAt(i) <= '9'))) {
                    checkValues = false;
                }
                if(!checkValues) {
                    return false;
                }
            }
            for(int i = 8 ; i < 18 ; i++) {
                if(!((userIdToAdd.charAt(i) >= 'a'
                        && userIdToAdd.charAt(i) <= 'f')
                        || (userIdToAdd.charAt(i) >= '0'
                        && userIdToAdd.charAt(i) <= '9'))) {
                    checkValues = false;
                }
                if(!checkValues) {
                    return false;
                }
            }
            return true;
        }
        return false;
    }
    return false;
}

The goal is to return true if the String looks like #[6 char long hex string]@[8 char long hex string], else we return false.

Here is the regex : /#[0-9a-f]{6}@[0-9a-f]{8}/

As you can see it looks like dirty, but, it is really bad besides REGEX, in terms of performance ?

Thank you in (GameBoy) advance (SP) !

Answer 1

Note that when you have a code with a lot of nested loops and conditionals, the first reflex is to try to design it better, example:

private boolean isHexChar(char c) {
    return (c > '/' && (c < ':' || c > '`' && c < 'g')); 
}

private boolean isIdCorrect(String userIdToAdd) {
    if( userIdToAdd.length() != 18 || userIdToAdd.charAt(0) != '#' || userIdToAdd.charAt(7) != '@') {
        return false;
    }

    for(int i=1; i<7; i++) {
        if (!isHexChar(userIdToAdd.charAt(i))) {
            return false;
        }
    }

    for(int i=8; i<18; i++) {
        if (!isHexChar(userIdToAdd.charAt(i))) {
            return false;
        }
    }

    return true;
}

Once done you can try to compare the speed with a regex (if you think it's important), but note that now the situation is different since you have a more readable (and probably faster) code.

Answer 2

There are a few reasons why you should probably use a regex.

• Readability. The Regex matching will be much easier to read (3 lines vs. ~30) than the if's and for-loops used here.
• It's the tool for the job. This is exactly what Regex's are for. Why re-invent the wheel (in a non-reusable way)?
• Performance. Despite what you may think, the Regex performance is not really bad enough to be considered here. In fact, it's probably better than the code you have written as a replacement. Only benchmarks will be able to tell.