用正则表达式替换字符串时未闭合的字符 class

Question

I want to remove a string at the beginning of another.

Example:

Begin	Removed	Final
"\n123: other"	Yes	other
"123: other"	No	Error
"\n4: smth"	Yes	smth
"123: a"	No	Error

Thanks to Regexr , I made this regex:

/[\\][n](?:[0-9]*)[ ][:]/g

I tried to use it in Java. With string.matches() I don't have any error. But, with string.replaceFirst , I have this error:

java.util.regex.PatternSyntaxException: Unclosed character class near index 24
/[\][n](?:[0-9]*)[ ][:]/g
                        ^

What I tried else?

• Remove / at begin and /g at end.
• Add (pattern) (such as visible in regex here )
• Multiple others quick way, but I the error is always at the last char of my regex

My full code:

String str = "\n512 : something"; // I init my string
if(str.matches("/[\\][n](?:[0-9]*)[ ][:]/g"))
   str = str.replaceFirst("/[\\][n](?:[0-9]*)[ ][:]/g", "");

How can I fix it? How can I solve my regex pattern?

Answer 1

You can use

.replaceFirst("\n[0-9]+\\s+:\\s*", "")

The regex matches

• \n - a newline char (you have a newline in the string, not a backslash and n )
• [0-9]+ - one or more digits
• \s+ - one or more whitespaces
• : - a colon
• \s* - zero or more whitespaces

See the Java demo :

List<String> strs = Arrays.asList("\n123 : other", "123 : other", "\n4 : smth", "123 : a");
for (String str : strs)
    System.out.println("\"" + str.replaceFirst("\n[0-9]+\\s+:\\s*", "") + "\"");

Output:

"other"
"123 : other"
"smth"
"123 : a"