Replacing characters in String using Meta characters or character classes

I am writing to remove all non-alphanumeric characters in a String with only lowercase letters.

I am using the replaceAll function and have looked at a few regexes

My reference is from: https://www.vogella.com/tutorials/JavaRegularExpressions/article.html which shows that

• \s : A whitespace character, short for [ \t\n\x0b\r\f]
• \W : A non-word character [^\w]

I tried the folllowing in Java but the results didn't remove the spaces or symbols:

lowercased = lowercased.replaceAll("\\W\\s", "");

output:

amanaplanac analp anam a

May I know what is wrong?

Regex \W\s means "a non-word character followed by a whitespace character".

If you want to replace any character that is one of those, use one of these:

• \W|\s where | means or

• [\W\s] where [ ] is a character class that in this case merges the built-in special character classes \W and \s, because that's what those are.

Of the two, I recommend using the second.

Of course, having \s there is redundant, because \s means whitespace character, and \W means non-word character, and since whitespaces are not word characters, using \W alone is enough.

lowercased = lowercased.replaceAll("\\W+", "");

Use | (or operator) like \W|\s since both \W and \s are independent case for which you want to replace. And since whitespace are not word character you can use \W only.

lowercased = lowercased.replaceAll("\\W|\\s", "");

Regex \W is meant for matching character's that are not numbers(0-9), alphabets(A-Z and a-z) and underscore (_). And /s is meant for matching space.

As /W already take care for matching non alphanumeric characters (excluding underscore). No need to use \s.

So if you are using \W you are allowing underscore(_) with alphanumeric values.

use the following to exclude underscore as well.

lowercased = lowercased.replaceAll("\\W|_", "");