Java REGEX, remove two different type of comments from String

Question

I have a text with two types of comments. The ones delimited by % and the ones that start with /* and end with */. For instance:

INPUT1: Sarah was going out. % Remember she usually doesn't go out % It was very cold.

DESIRED_OUTPUT1: Sarah was going out. It was very cold.

INPUT2: Sarah was going out. /* Remember she usually doesn't go out */ It was very cold.

DESIRED_OUTPUT2: Sarah was going out. It was very cold.

INPUT3: Charles knocked on the door and a woman opened it. % Hmm, is this good... /* Not sure */ Perhaps this should happen in chapter 10 instead? % She looked at him. - Yes?, she said.

DESIRED_OUTPUT3: Charles knocked on the door and a woman opened it. She looked at him. - Yes?, she said.

INPUT4: Charles knocked on the door and a woman opened it. % Hmm, is this good... /* Not sure to 100% */ Perhaps this should happen in chapter 10 instead? % She looked at him. - Yes?, she said.

DESIRED_OUTPUT4: Charles knocked on the door and a woman opened it. */ Perhaps this should happen in chapter 10 instead?

Basically, I would like that when encountering an opening comment mark, everything is removed until its respective closing comment mark (even if this means removing comment marks of the other type).

If a comment is opened, either with % or /*, but never closed, the comment is assumed to continue until the end of the text. However, if it is present just a closing mark of this kind */ (because the opener was inside another comment and hence removed), it should be left in the text.

I think Input 4 should result in Charles knocked on the door and a woman opened it. */ Perhaps this should happen in chapter 10 instead? % She looked at him. - Yes?, she said.. You seem to want .replaceAll("%[^%]*%|/\\*[^*]*\\*+(?:[^/*][^*]*\\*+)*/",""). There is a chance you need to make the last % optional though, "%[^%]*%?|/\\*[^*]*\\*+(?:[^/*][^*]*\\*+)*/". — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jun 7, 2020 at 9:39
Well, thank you for pointing that out. I forgot to mention that whether there is no closing mark (or just a closing one, since the opening was inside another comment and hence removed, like in this case) the mark should stay there. So Input/output 4 is correct. — dadadima
– dadadima, Commented Jun 7, 2020 at 9:45
So, acc. to what you say ("the mark should stay there"), the % She looked at him. - Yes?, she said. should not be removed in Input 4. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jun 7, 2020 at 9:47
Well, you are right again. If a comment is opened, either with % or / *, but never closed, the comment is assumed to continue until the end of the text. — dadadima
– dadadima, Commented Jun 7, 2020 at 9:53
Aha, so you probably want .replaceAll("%[^%]*%?|/\\*[^*]*(?:\\*(?!/)[^*]*)*(?:\\*/)?","") — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jun 7, 2020 at 9:57

Wiktor Stribiżew · Accepted Answer · 2020-06-07 10:10:25Z

3

You may use

.replaceAll("%[^%]*%?|/\\*[^*]*(?:\\*(?!/)[^*]*)*(?:\\*/)?","")

See the regex demo

Details

%[^%]*%? - %...% like comments with an optional trailing delimiter:
- % - a % char
- [^%]* - 0 or more chars other than %
- %? - an optional % char
| - or
/\*[^*]*(?:\*(?!/)[^*]*)*(?:\*/)? - /*...*/ like comments with an optional trailing delimiter:
- /\* - /* string
- [^*]* - 0 or more chars other than *
- (?:\*(?!/)[^*]*)* - 0 or more occurrences of
  - \*(?!/) - a * not followed with /
  - [^*]* - 0 or more chars other than *
- (?:\*/)? - an optional */ substring.

answered Jun 7, 2020 at 10:10

Wiktor Stribiżew

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