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Thread: Validating UK postcodes

  1. #1
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    Default Validating UK postcodes

    In general, the UK postcode format is one of "A9 9AA", "A99 9AA", "AA9 9AA", "AA99 9AA", "A9A 9AA" or "AA9A 9AA", where A is an alphabetic character and 9 is a numeric character.
    Write a Java program to validate postcode input for each of these formats.

     public class ValidatingPostcodes
        public static boolean validateFirst4Integers( String First4Integers )
            return First4Integers.matches( "[a-z]")

    Its not much but I dont know what to do.. HELP!

  2. #2
    Join Date
    Jun 2012
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    Default Re: Validating UK postcodes

    Quote Originally Posted by Mehwish-S View Post
    ...Its not much ...
    Well, it's a start.

    I perceive that you have already recognized that you need a regular expression.

    I would make three Strings since it's easier to test one thing at a time.

    I would probably call the Strings "firstPart," "separator," and "isecondPart."

    Then the regular expression String used in the String.matches() statement in the final program would simply be firstPart + separator + isecondPart.

    OK, let's get started...

    I would (probably) do the easy part first:
    The "separator" is a single space, right? (Wow! We are one third of the way through already!)

    Then, I would try to express the other parts in Human Language in a form that can be translated to Regular Expression lingo as spelled out in the Java Regular Expression Tutorial

    From your description, I think the Strings would be defined something like the following:

    • firstPart:

      One or two Letters followed by
      One or two Digits followed by
      Zero or one Letter

    • separator:

      One Space

    • secondPart:

      One Digit followed by
      Two Letters

    Letter: [A-Z]
    Digit: [0-9]
    Space: [ ]

    In the tutorial, here's where it tells you how you handle repeated fields: Regular Expression Quantifiers

    Now if my description turns out not to be completely accurate in terms of accepting valid codes and/or rejecting invalid codes (I'm a Yank, you know; English is just another Foreign Language to me), then you might be able to use my thoughts as a starting point and refine things if your testing turns up problems.

    Bottom line:
    Test, test, and test some more. Give lots of valid codes, but don't just give it Good Stuff; try to find Bad Stuff that is "almost-but-not-quite" Good.


    Last edited by Zaphod_b; July 28th, 2012 at 03:29 PM.

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