Java Regex-matches anything except three specific string

Question

Given such Java Regex codes:

Pattern pattern = Pattern.compile("[^(bob)(alice)(kitty)]");
String s = "a";
Matcher matcher = pattern.matcher(s);

boolean bl = matcher.find();
System.out.println(bl);

The output is false. Why? The regex [^(bob)(alice)(kitty)] matches any things except bob, alice or kitty. Then the result should be true, right?

Answer 1

Because your regex is not doing what you think it should be doing.

Use this regex with Negative lookahead:

Pattern pattern = Pattern.compile("^(?!bob|alice|kitty).*$");

Your regex: [^(bob)(alice)(kitty)] is using a character class and inside a character class there are no groups.

• (?!bob|alice|kitty) is negative lookahead that means fail the match if any of these 3 words appear at start of input.
• Important to use anchors ^ and $ to make sure we're not matching from middle of the string.

• If you want to avoid matching these 3 words anywhere in input then use this regex:

  ^(?!.*?(?:bob|alice|kitty)).*$
  

RegEx Demo