regex not removing underscore from pattern

Hari Bisht :

I was trying to code for allowing certain special characters in a string by using java.util.regex.Matcher and java.util.regex.pattern but this is not removing underscore from the same. I'm new here. I need help on this. Code extract below:

  // String to be scanned to find the pattern.
  String line = "This order was _:$ placed for QT3000! OK?";
  String pattern = "[^\\w\\s\\-?:().,'+\\/]";
  String s = null;

  // Create a Pattern object
  Pattern r = Pattern.compile(pattern);

  // Now create matcher object.
  Matcher m = r.matcher(line);
  s= m.replaceAll("");
  System.out.println("Output: " + s);

Expected: This order was : placed for QT3000 OK? Actual : This order was _: placed for QT3000 OK?

Wiktor Stribiżew :

The \w pattern matches underscores and [^\w] matches any char but letters, digits and an underscore.

Replace with \p{Alnum}:

String pattern = "[^\\p{Alnum}\\s?:().,'+/-]";

Note I put the hyphen at the end of the character class so as not to escape it and remove the escaping \ from the / as it is not a special regex metacharacter.

See the Java regex demo.

The [^\\p{Alnum}\\s?:().,'+/-] pattern matches any char but:

• \p{Alnum} - alphanumeric [a-zA-Z0-9]
• \s - whitespaces
• ? - a question mark
• : - a colon
• ( - a ( symbol
• ) - a ) symbol
• . - a dot
• , - a comma
• ' - a single quotation mark
• + - a plus
• / - a forward slash
• - - a hyphen.