Question

I’m a Java user but I’m new to regular expressions.

I just want to have a tiny expression that, given a word (we assume that the string is only one word), answers with a boolean, telling if the word is valid or not.

An example… I want to catch all words that is plausible to be in a dictionary… So, i just want words with chars from a-z A-Z, an hyphen (for example: man-in-the-middle) and an apostrophe (like I’ll or Tiffany’s).

Valid words:

• "food"
• "RocKet"
• "man-in-the-middle"
• "kahsdkjhsakdhakjsd"
• "JESUS", etc.

Non-valid words:

• "gipsy76"
• "www.google.com"
• "[e-mail]"
• "745474"
• "+-x/", etc.

I use this code, but it won’t gave the correct answer:

Pattern p = Pattern.compile("[A-Za-z&-&']");
Matcher m = p.matcher(s);
System.out.println(m.matches());

What’s wrong with my regex?

Answer 1

• Add a + after the expression to say “one or more of those characters”:
• Escape the hyphen with \ (or put it last).
• Remove those & characters:

Here’s the code:

Pattern p = Pattern.compile("[A-Za-z'-]+");
Matcher m = p.matcher(s);
System.out.println(m.matches());

---

Complete test:

String[] ok = {"food","RocKet","man-in-the-middle","kahsdkjhsakdhakjsd","JESUS"};
String[] notOk = {"gipsy76", "www.google.com", "[e-mail]", "745474","+-x/" };

Pattern p = Pattern.compile("[A-Za-z'-]+");

for (String shouldMatch : ok)
    if (!p.matcher(shouldMatch).matches())
        System.out.println("Error on: " + shouldMatch);

for (String shouldNotMatch : notOk)
    if (p.matcher(shouldNotMatch).matches())
        System.out.println("Error on: " + shouldNotMatch);

(Produces no output.)