Using regex to validate a field

Question

Sorry for being new to programming. Apparently I'm expected to know everything about the topic before posting here. I've only been doing this 3 weeks, learning as I go.

I've got a field limited to 5 characters I'm trying to validate. The first character must be a letter, and the following 4 characters must be numbers. Regex is like Greek to me at this point, so I'm having trouble. I've been able to get the first character validated, but I'm stumped on the remaining 4. Here's my code:

if (carID.substring(0, 1).matches("[0-9]")) {
    showDataFormatError();
    break;
} else {
    if (carID.substring(1, 5).matches("[a-zA-Z]")) {
    showDataFormatError();
    break;
    }
}

Updating to demonstrate my horrible coding at this point.

            if (carID.length() < 5) {
                showDataLengthError();
                break;
            } else {
                if (carID.matches("^[a-zA-Z][0-9]{4}$")) {
                    showDataFormatError();
                    break;
                } else {
                    if (carYearString.length() < 0) {
                        showDateLengthError();
                        break;
                    } else {
                        try {
                            int carYear = Integer.parseInt(carYearString);
                            int currentYear = Calendar.getInstance().get(
                                    Calendar.YEAR);

// etc.

You are calling showDataFormatError() when the data is correct. You need if (!carID.matches ... — andy256
– andy256, Commented Aug 29, 2013 at 5:18

andy256 · Accepted Answer · 2013-08-29 04:49:52Z

2

Try this

boolean valid = carID.matches("^[a-zA-Z][0-9]{4}$");

And see the tutorial

EDIT thanks to the down voter I spotted and fixed the error.

answered Aug 29, 2013 at 4:49

andy256

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1 Comment

andy256 Over a year ago

Can you give an example? ` String carID = "a1234"; boolean valid = carID.matches("^[a-zA-Z][0-9]{4}$"); System.out.println("carID "+valid); ` outputs ` carID true `

Rahul Kulhari · Accepted Answer · 2013-08-29 05:21:19Z

2

If you want to make sure the entire string is that format, use:

^[a-zA-Z]\d{4}$

this will help you and for tutorial you should have to go through this link

Regular Expression

answered Aug 29, 2013 at 5:21

Rahul Kulhari

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Comments

hwnd · Accepted Answer · 2013-08-29 06:00:28Z

1

I would do something like..

\pL       Matches Any kind of letter from any language.
\pN{4}    Matches Any kind of numeric character in any script. (4 times) greedy.

...

if (carID.length() > 5) throw IllegalArgumentException();

if (carID.matches("^\pL\pN{4}$")){
  return true;
} else {
  return false;

  ...
}

answered Aug 29, 2013 at 6:00

hwnd

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