what does this regex mean [^}]*

Question

This is a code I read on a forum.

public String replaceVariables(String input, Map<String, String> context) {
    if(context == null || input == null)
        return input;

    Matcher m = Pattern.compile( "\\$\\{([^}]*)\\}" ).matcher( input );
    // Have to use a StringBuffer here because the matcher API doesn't accept a StringBuilder -kg
    StringBuffer sb = new StringBuffer();
    while(m.find()) {
        String value = context.get(m.group(1));
        if(value != null)
            m.appendReplacement(sb, value);
    }
    m.appendTail(sb);
    return sb.toString();
}

I am confuse about [^}]*. Can I use another character instead of }?

Did you read e.g. http://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html? — Oliver Charlesworth, May 10 '15 at 13:28
http://stackoverflow.com/questions/22937618/reference-what-does-this-regex-mean/22944075#22944075 — Alex Salauyou, May 10 '15 at 13:34
Literally: "any character which is _not_ a closing bracket (`[^}]`), zero or more times (`*`)". — fge, May 10 '15 at 13:42

score 5 · Accepted Answer · edited May 23 '17 at 10:26

5

The [] is used in regular expression to denote a set of characters.

The ^ denotes the not operator. However, note that if the ^ is not the first character in the set, it won't be treated as an operation, but rather as a character. For example, [1^2] matches 1, ^ and 2 (not 1 and anything that's not 2) (thanks to @Maroun Maroun)

Therefore, [^}] denotes a set of characters that's comprised of characters which are not }.

The * means that there can be infinite (including zero) repetitions of the set.

edited May 23 '17 at 10:26

Community

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answered May 10 '15 at 13:28

Konstantin Yovkov

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Good answer, but you might add that the `*` allows for zero repetitions. I.e., there don't have to be any non-`}` characters at all for the regex to match the string. – elixenide May 10 '15 at 13:53
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Also note that if `^` is not the first character, it'll loose its meaning. For example, `[1^2]` matches 1, ^ and 2 (not 1 and anything that's not 2). – Maroun May 10 '15 at 14:23
Thanks, Maroun. Added that too. :) – Konstantin Yovkov May 10 '15 at 14:27

what does this regex mean [^}]*

1 Answers1