Validating ZIP codes

Postal codes are generally formatted specific to their country or local requirements. For this reason, regular expressions are useful because they can accommodate any postal code required. The example that follows demonstrates how to validate a standard United States postal code, with or without the hyphen and last four digits:

public static void validateZip(String zip){ 
      String zipRegex = "^[0-9]{5}(?:-[0-9]{4})?$"; 
      Pattern pattern = Pattern.compile(zipRegex); 
      Matcher matcher = pattern.matcher(zip); 
      if(matcher.matches()){ 
            out.println(zip + " is a valid zip code"); 
      }else{ 
            out.println(zip + " is not a valid zip code"); 
      } 
} 

We make the following method calls to test our data:

out.println(validateZip("12345")); 
out.println(validateZip("12345-6789")); 
out.println(validateZip("123")); 

The output follows:

12345 is a valid zip code
12345-6789 is a valid zip code
123 is not a valid zip code