Question

I need help with this matter. Look at the following regex:

Pattern pattern = Pattern.compile("[A-Za-z]+(\\-[A-Za-z]+)");
Matcher matcher = pattern.matcher(s1);

I want to look for words like this: “home-made”, “aaaa-bbb” and not “aaa – bbb”, but not
“aaa–aa–aaa”. Basically, I want the following:

word – hyphen – word.

It is working for everything, except this pattern will pass: “aaa–aaa–aaa” and shouldn’t. What regex will work for this pattern?

Answer 1

Can can remove the backslash from your expression:

"[A-Za-z]+-[A-Za-z]+"

The following code should work then

Pattern pattern = Pattern.compile("[A-Za-z]+-[A-Za-z]+");
Matcher matcher = pattern.matcher("aaa-bbb");
match = matcher.matches();

Note that you can use Matcher.matches() instead of Matcher.find() in order to check the complete string for a match.

If instead you want to look inside a string using Matcher.find() you can use the expression

"(^|\\s)[A-Za-z]+-[A-Za-z]+(\\s|$)"

but note that then only words separated by whitespace will be found (i.e. no words like aaa-bbb.). To capture also this case you can then use lookbehinds and lookaheads:

"(?<![A-Za-z-])[A-Za-z]+-[A-Za-z]+(?![A-Za-z-])"

which will read

(?<![A-Za-z-])        // before the match there must not be and A-Z or -
[A-Za-z]+             // the match itself consists of one or more A-Z
-                     // followed by a -
[A-Za-z]+             // followed by one or more A-Z
(?![A-Za-z-])         // but afterwards not by any A-Z or -

An example:

Pattern pattern = Pattern.compile("(?<![A-Za-z-])[A-Za-z]+-[A-Za-z]+(?![A-Za-z-])");
Matcher matcher = pattern.matcher("It is home-made.");
if (matcher.find()) {
    System.out.println(matcher.group());    // => home-made
}