[java] Regex to match words of a certain length

I would like to know the regex to match words such that the words have a maximum length. for eg, if a word is of maximum 10 characters in length, I would like the regex to match, but if the length exceeds 10, then the regex should not match.

I tried

^(\w{10})$

but that brings me matches only if the minimum length of the word is 10 characters. If the word is more than 10 characters, it still matches, but matches only first 10 characters.

^\w{0,10}$ # allows words of up to 10 characters.
^\w{5,}$   # allows words of more than 4 characters.
^\w{5,10}$ # allows words of between 5 and 10 characters.

Length of characters to be matched.

{n,m}  n <= length <= m
{n}    length == n
{n,}   length >= n

And by default, the engine is greedy to match this pattern. For example, if the input is 123456789, \d{2,5} will match 12345 which is with length 5.

If you want the engine returns when length of 2 matched, use \d{2,5}?

Even, I was looking for the same regex but I wanted to include the all special character and blank spaces too. So here is the regex for that:

^[A-Za-z0-9\s$&+,:;=?@#|'<>.^*()%!-]{0,10}$

Method 1

Word boundaries would work perfectly here, such as with:

\b\w{3,8}\b
\b\w{2,}
\b\w{,10}\b
\b\w{5}\b

RegEx Demo 1

Java

Some languages such as Java and C++ are double-escape required:

\\b\\w{3,8}\\b
\\b\\w{2,}
\\b\\w{,10}\\b
\\b\\w{5}\\b

^{PS: \\b\\w{,10}\\b may not work for all languages or flavors.}

Test 1

import java.util.regex.Matcher;
import java.util.regex.Pattern;


public class RegularExpression{

    public static void main(String[] args){


        final String regex = "\\b\\w{3,8}\\b";
        final String string = "words with length three to eight";

        final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE);
        final Matcher matcher = pattern.matcher(string);

        while (matcher.find()) {
            System.out.println("Full match: " + matcher.group(0));
        }

    }
}

Output 1

Full match: words
Full match: with
Full match: length
Full match: three
Full match: eight

Method 2

Another good-to-know method is to use negative lookarounds:

(?<!\w)\w{3,8}(?!\w)
(?<!\w)\w{2,}
(?<!\w)\w{,10}(?!\w)
(?<!\w)\w{5}(?!\w)

Java

(?<!\\w)\\w{3,8}(?!\\w)
(?<!\\w)\\w{2,}
(?<!\\w)\\w{,10}(?!\\w)
(?<!\\w)\\w{5}(?!\\w)

RegEx Demo 2

Test 2

import java.util.regex.Matcher;
import java.util.regex.Pattern;


public class RegularExpression{

    public static void main(String[] args){


        final String regex = "(?<!\\w)\\w{1,10}(?!\\w)";
        final String string = "words with length three to eight";

        final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE);
        final Matcher matcher = pattern.matcher(string);

        while (matcher.find()) {
            System.out.println("Full match: " + matcher.group(0));
        }

    }
}

Output 2

Full match: words
Full match: with
Full match: length
Full match: three
Full match: to
Full match: eight

RegEx Circuit

jex.im visualizes regular expressions:

If you wish to simplify/modify/explore the expression, it's been explained on the top right panel of regex101.com. If you'd like, you can also watch in this link, how it would match against some sample inputs.