Adding square brackets to character class in Java regex

Question

I would like to read a content String from file lne by line, and in each line remove all caharcters that are not one of the following [ { } ] I wanted

Answer 1

In Java, the regex character classes can have unions and intersections, thus, [ and ] must be escaped inside if you want them to be treated as literal symbols. And since \ can be used to define escape sequences, it should be doubled to denote a literal regex-escaping \.

Use

line = line.replaceAll("[^\\[({})\\]]","");
                          ^^     ^^