删除除了匹配正则表达式java的所有文本

Question

I have regexp, that should delete comments(ye, it's bad, but for me it works)

String regex = (^\/\/.*)|(\s+\/\/.*)|((\/\*)(.|\n)+?(\*\/));

this code should delete all commtents

Pattern.compile(regex).matcher(some text).replaceAll(" ");

but how can i make it to delete all EXCEPT regexp?

For example: if i have string like this:

/*Comments it's cool*/ public static void foo(){}

my regexp match comments, but i need to delete what doesn't match, so it will look like:

/*Comments it's cool*/

Answer 1

Basically, you can just match what your regex matches, and concatenate the matched texts. It is much easier.

As for the regex that removes all but what your original pattern matches, you can use consider capturing your whole pattern with a capturing optional group and use a . to match any char after it.

Say, your pattern is abc . It matches abc . But now, you need to match the opposite, everything that your regex does not match. Use

(?s)(abc)?.

And replace with $1 . See the regex demo .

Some adjustment may be necessary though for newlines. If you do not want to remove newlines, do not use the DOTALL modifier. If you want to use it, replace . with [^\\n\\r] in the original pattern. Remember, you will be able to shrink the empty lines with some (\\r?\\n|\\r){2,} pattern (and again, $1 backreference).

So, your regex is

String regex = "^\\s*//.*|/\*[^*]*\*+(?:[^/*][^*]*\*+)*/";

where /\\*[^*]*\\*+(?:[^/*][^*]*\\*+)*/ matches multiline comments, and ^\\\\s*//.* matches singleline comments.

To make it remove all but what it matches, use

String regex = "(?sm)(^\\s*//[^\r\n]*|/\\*[^*]*\\*+(?:[^/*][^*]*\\*+)*/)?.";

and replace with $1 backreference. See the regex demo (based on ClasG demo ). Note I also added a (?m) MULTILINE modifier for the ^ to match at the beginning of the line.