Using square brackets inside character class in Java regex

Question

Below is the regex I have written to replace the special chars &!)(}{][^"~*?:;\+- from a string, but somehow it is not able to replace [ & ] from it as it acts as beginning and closing of regex. How can I do that?

System.out.println(" &!)(}{][^\"~*?:;\\+-".replaceAll("[| |&|!|)|(|}|{|^|\"|~|*|?|:|;|\\\\|+|-]", "_"));
}

The output for now : _______][__________

`System.out.println(" &!)(}{][^\"~*?:;\\+-".replaceAll("[\\[\\] &!)(}{^\"~*?:;\\\\+-]", "_")); `Here is your code improved a bit, no need for all the `|`'s. The way to go is to escape the brackets. you do that by puting a `\` before it, but in the case of java you need to escape the `\` itself therefore you put two `\`'s before the bracket. :) — fill͡pant͡, Jan 10 '17 at 12:30
Actually, `|` in the pattern was a bug. Removing it from the character class is not just an improvement, it is a fix. — Wiktor Stribiżew, Jan 10 '17 at 12:35

score 8 · Accepted Answer · edited Jun 01 '19 at 07:45

You just need to escape the [ and ] inside a character class in a Java regex.

Also, you do not need to put | as alternation symbol in the character class as it is treated as a literal |.

System.out.println(" &!)(}{][^\"~*?:;\\+-".replaceAll("[\\]\\[ &!)(}{^\"~*?:;\\\\+-]", "_"));
// => ___________________

See the Java demo

†: _{Note that in PCRE/Python/.NET, POSIX, you do not have to escape square brackets in the character class if you put them at the right places: []ab[]. In JavaScript, you always have to escape ]: /[^\]abc[]/. In Java and ICU regexps, you must always escape both [ and ] inside the character class. – Wiktor Stribiżew Jan 10 '17 at 12:39}

Using square brackets inside character class in Java regex

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