java phone number validation....

Question

Here is my problem:

Create a constructor for a telephone number given a string in the form xxx-xxx-xxxx or xxx-xxxx for a local number. Throw an exception if the format is not valid.

So I was thinking to validate it using a regular expression, but I don't know if I'm doing it correctly. Also what kind of exception would I have to throw? Do I need to create my own exception?

    public TelephoneNumber(String aString){
        if(isPhoneNumberValid(aString)==true){
            StringTokenizer tokens = new StringTokenizer("-");
            if(tokens.countTokens()==3){
                areaCode = Integer.parseInt(tokens.nextToken());
                exchangeCode = Integer.parseInt(tokens.nextToken());
                number = Integer.parseInt(tokens.nextToken());
            }
            else if(tokens.countTokens()==2){
                exchangeCode = Integer.parseInt(tokens.nextToken());
                number = Integer.parseInt(tokens.nextToken());
            }
            else{
                //throw an excemption here
            }
        }

    }


 public static boolean isPhoneNumberValid(String phoneNumber){
     boolean isValid = false;

     //Initialize reg ex for phone number.
    String expression = "(\\d{3})(\\[-])(\\d{4})$";
    CharSequence inputStr = phoneNumber;
    Pattern pattern = Pattern.compile(expression);
    Matcher matcher = pattern.matcher(inputStr);
    if(matcher.matches()){
        isValid = true;
     }
        return isValid;
    }

Hi sorry, yes this is homework. For this assignments the only valid format are xxx-xxx-xxxx and xxx-xxxx, all other formats (xxx)xxx-xxxx or xxxxxxxxxx are invalid in this case.

I would like to know if my regular expression is correct

Answer 1

So I was thinking to validate it using a regular expression, but I don't know if I'm doing it correctly.

It indeed looks overcomplicated. Also, matching xxx-xxx-xxxx or xxx-xxxx where x is a digit can be done better with "(\\d{3}-){1,2}\\d{4}". To learn more about regex I recommend to go through http://regular-expressions.info.

Also what kind of exception would I have to throw? Do I need to create my own exception?

A ValidatorException seems straight forward.

public static void isPhoneNumberValid(String phoneNumber) throws ValidatorException {
    if (!phoneNumber.matches(regex)) {
        throws ValidatorException("Invalid phone number");
    }
}

If you don't want to create one yourself for some reasons, then I'd probably pick IllegalArgumentException, but still, I don't recommend that.

That said, this validation of course doesn't cover international and/or external telephone numbers. Unless this is really homework, I'd suggest to rethink the validation.

Answer 2

You could match those patterns pretty easily as suggested by BalusC.

As a side note, StringTokenizer has been deprecated. From JavaDoc:

StringTokenizer is a legacy class that is retained for compatibility reasons although its use is discouraged in new code. It is recommended that anyone seeking this functionality use the split method of String or the java.util.regex package instead.

An easier way to split your string into the appropriate segments would be:

String phoneParts[] = phoneNumber.split("-");