Verify code format in Java

Question

I'm working on a project for school in which we must verify the format of a code. The format is 3 capital letters followed by 3 digits where at least 1 digit is not a 0. So ABC001 is valid. ABC000 is not valid.

Where I'm stuck is how I'd write the format to validate the digits so that 000 is invalid while 001-999 is valid. Below is the code, it's currently written so that 000 is valid.

public static boolean validateInvoiceCode(String invoiceCode)
{
      return invoiceCode.matches("[A-Z][A-Z][A-Z][0-9][0-9][0-9]");
}

Answer 1

Add a negative lookbehind (?<!...) that blacklists 000:

[A-Z][A-Z][A-Z][0-9][0-9][0-9](?<!000)

Regex101 Demo

You may also want to improve your regex by using quantifiers, and \d for digits:

[A-Z]{3}\\d{3}(?<!000)

Regex101 Demo