Java program on netbeans (Validating 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.

Code:

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

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I know its not much but i dont know what else to put in ... HELP!