Java replaceAll - Replace "/**" with ""

Question

I am currently doing comment analysis with some Java code and needed to do the following opperation:

comment = comment.replaceAll("/**", "");

But I am meet with this Exception:

    Exception in thread "main" java.util.regex.PatternSyntaxException: Dangling meta character '*' near index 2
/**
  ^
    at java.util.regex.Pattern.error(Unknown Source)
    at java.util.regex.Pattern.sequence(Unknown Source)
    at java.util.regex.Pattern.expr(Unknown Source)
    at java.util.regex.Pattern.compile(Unknown Source)
    at java.util.regex.Pattern.<init>(Unknown Source)
    at java.util.regex.Pattern.compile(Unknown Source)
    at java.lang.String.replaceAll(Unknown Source)
    at commentCoupler.coupler.commentCriteriaForfilled(coupler.java:234)
    at commentCoupler.coupler.analyze(coupler.java:64)
    at commentCoupler.coupler.recursiveCoupler(coupler.java:27)
    at commentCoupler.coupler.recursiveCoupler(coupler.java:22)
    at commentCoupler.coupler.recursiveCoupler(coupler.java:22)
    at commentCoupler.main.main(main.java:16)

Edit: The exception also occurs when I do

comment = comment.replaceAll("**/", "");

and

comment = comment.replaceAll("*/", "");

Do anyone know why this happens and do anyone have a workaround?

`*` is a reserved character in regex. You need to escape it. — Drew Kennedy, May 12 '15 at 13:48
@DrewKennedy I can't seem to escape *, eclipse tells me that is not a valid escape char. — Fruitdrops13, May 12 '15 at 13:55
@TheLostMind Habit? But that fixed the problem as also answered by aioobe — Fruitdrops13, May 12 '15 at 13:55
`"/\*\*"` is the regex you need, but because it's in a java String I think you'll need `"/\\*\\*"`. Annoying, I know. It's really funny trying to find '\' because you end up doing `"\\\\"`. See [this](http://stackoverflow.com/a/20669000/1858327) for better explanation. — Captain Man, May 12 '15 at 13:56
@CaptainMan You are exactly right, however my problem was easier fixed by using `replace` instead of `replaceAll` — Fruitdrops13, May 12 '15 at 14:05

aioobe · Accepted Answer · 2015-05-12T13:49:46.953

6

replaceAll takes a regular expression, and /** isn't a valid regular expression.

If you just want to remove /**, use replace instead.

edited May 12 '15 at 13:49

answered May 12 '15 at 13:49

aioobe

413,195
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score 2 · Answer 2 · answered May 12 '15 at 13:58

2

First parameter of "replaceAll" is a regular expression, and character "*" has a special meaning in regular expressions.

You can use something like this:

String a = "/**hola mundo/**, adios mundo";
String output = a.replaceAll("/\\*\\*", "");
System.out.println(output); // --> "hola mundo, adios mundo"

answered May 12 '15 at 13:58

srcarro

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Ahh, thanks, I understand now. Forgot that * is the wildcard char in regex. – Fruitdrops13 May 12 '15 at 13:59
The reason this is the way it is is because the proper regex is `/\*\*` and the backslash needs to be escaped in the java string. – Captain Man May 12 '15 at 14:25

score 0 · Answer 3 · answered May 12 '15 at 13:50

0

comment = comment.replaceAll("/\**", "");

answered May 12 '15 at 13:50

Dagriel

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Eclipse answers: "Invalid escape sequence (valid ones are \b \t \n \f \r \" \' \\ )" – Fruitdrops13 May 12 '15 at 13:57
1

Not only is this regex but also a java string, \ must be escaped for java String level and * must be escaped for regex level. `/\\*\\*` is correct. – Captain Man May 12 '15 at 14:20
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Besides the comments here, it is always preferable if you also explain your solution. If anything, it lets you think through your answer. – Magnilex May 12 '15 at 19:55

Captain Man · Answer 4 · 2015-05-12T20:30:03.007

Two things are wrong with this code:

comment = comment.replaceAll("/**", "");

* is a special regex character to match any number of any characters, based on the context that you are removing comments you want to match the literal * so you need your regex to be /\*\*.
Because this regex is inside a java String it will try to read \* as an escape code (like \n being newline character), but \* isn't one. It needs to be \\* instead, meaning the String should be /\\*\\*

This is correct.

comment = comment.replaceAll("/\\*\\*", "");

As an aside, even if \* was a valid escape code, the thing it got replaced with would be passed into regex, not \*. (e.g., if you put \n in the newline character would go into regex, not a backslash and a lowercase n.

You may want to go with something like this though

comment = comment.replaceAll("/\\**\\*/", "");

which would be removing /* <stuff> */. This catches doc-comments and regular multi-line comments in addition to removing the entire comment. It depends on how you've read the string though.

Java replaceAll - Replace "/**" with ""

4 Answers4