String pattern matching problem in Java

Question

In my program when I\'m using

line.replaceAll(\"(\", \"_\");

I got a RuntimeException:

 at java.util.regex.Pattern         


        

Answer 1

The first argument to string.replaceAll is a regular expression, not just a string. The opening left bracket is a special character in a regex, so you must escape it:

line.replaceAll("\\(", "_");

Alternatively, since you are replacing a single character, you could use string.replace like so:

line.replace('(', '_');

Answer 2

The error message above the stack trace is (somewhat) helpful:

Exception in thread "main" java.util.regex.PatternSyntaxException: Unclosed group near index 1 ( ^

(That's what I get in Java 6.) It mentions "regex", "group", and the parenthesis. If you can't see this message, you should check how you're logging/catching/displaying exceptions. It could save you some trouble in the future.