Is there a not (!) operator in regexp?

Question

I need to remove all characters from the given string except for several which should left. How to do that with regexp?

Simple test: characters[1, a, *] shouldn't be removed, all other should from string "asdf123**".

Answer 1

There is: ^ in a set.

You should be able to do something like:

text = text.replaceAll("[^1a*]", "");

Full sample:

public class Test
{
    public static void main(String[] args)
    {
        String input = "asdf123**";
        String output = input.replaceAll("[^1a*]", "");
        System.out.println(output); // Prints a1**
    }
}

Answer 2

When used inside [ and ] the ^ (caret) is the not operator.

It is used like this:

"[^abc]"

That will match any character except for a b or c.

Answer 3

There's a negated character class, which might work for this instance. You define one by putting ^ at the beginning of the class, such as:

[^1a\*]

for your specific case.