正则表达式只允许 1 个破折号

Question

I have a textbox where I get the last name of a user. How do I allow only one dash (-) in a regular expression? And it's not supposed to be in the beginning or at the end of the string.
I have this code:

Pattern p = Pattern.compile("[^a-z-']", Pattern.CASE_INSENSITIVE);
Matcher m = p.matcher(name);

Answer 1

Try to rephrase the question in more regexy terms. Rather than "allow only one dash, and it can't be at the beginning" you could say, "the string's beginning, followed by at least one non-dash, followed by one dash, followed by at least one non-dash, followed by the string's end."

• the string's beginning: `^
• at least one non-dash: [^-]+
• followed by one dash: -
• followed by at least one non-dash: [^-]+
• followed by the string's end: $

Put those all together, and there you go. If you're using this in a context that matches against the complete string (not just any substring within it), you don't need the anchors -- though it may be good to put them in anyway, in case you later use that regex in a substring-matching context and forget to add them back in.

Answer 2

Why not just use indexOf() in String ?

String s = "last-name";
int first = s.indexOf('-');
int last = s.lastIndexOf('-');

if(first == 0 || last == s.length()-1) // Checks if a dash is at the beginning or end
    System.out.println("BAD");
if(first != last) // Checks if there is more than one dash
    System.out.println("BAD");

It is slower than using regex but with usually small size of last names it should not be noticeable in the least bit. Also, it will make debugging and future maintenance MUCH easier.

Answer 3

This regex represents one or more non-hyphens , followed by a single hyphen, followed by one or more non-hyphens .

^[^\-]+\-[^\-]+$

I'm not sure if the hyphen in the middle needs to be escaped with a backslash... That probably depends on what platform you're using for regex.

Answer 4

It looks like your regex represents a fragment of an invalid value, and you're presumably using Matcher.find() to find if any part of your value matches that regex. Is that correct? If so, you can change your pattern to:

Pattern p = Pattern.compile("[^a-zA-Z'-]|-.*-|^-|-$");

which will match a non-letter-non-hyphen-non-apostrophe character, or a sequence of characters that both starts and ends with hyphens (thereby detecting a value that contains two hyphens), or a leading hyphen, or a trailing hyphen.

Answer 5

Try pattern something like [az] -[az] .

Pattern p = Pattern.compile("[az] -[az] ");