Question

I need to check a String is "\++?" which will match something like +6014456

But I get this error message invalid escape sequence (valid ones are \b \t \n \f \r \" \' \\) …. why?

Answer 1

It’s giving you an error because "\++?" isn’t a valid Java literal – you need to escape the backslash. Try this:

Pattern pattern = Pattern.compile("\\++?");

However, I don’t think that’s actually the regular expression you want. Don’t you actually mean something like:

Pattern pattern = Pattern.compile("\\+\\d+");

That corresponds to a regular expression of \+\d+, i.e. a plus followed by at least one digit.