CustomerNumber.java

/**
 * This program test a customer ID to
 * verify that it is in the proper format.
 */

import java.util.*;

public class CustomerNumber 
{
    public static void main(String[] args) 
    {
        String input;
        
        Scanner keyboard = new Scanner (System.in);
        
        System.out.println("Enter a customer ID in the form LLLNNNN");;
        System.out.print("(LLL = letters and NNNN = numbers): ");
        input = keyboard.nextLine();
        
        if (isValid(input))
            System.out.println("That's a valid customer ID.");
        else 
        {
            System.out.println("That is not the proper format of " +
                                "a customer ID.");
            System.out.println("Here is an example: ABC1234");
        }
    }
    
    private static boolean isValid(String custID)
    {
        boolean goodSoFar = true;  //Flag
        int i= 0;
        
        //Test the length
        if(custID.length() != 7)
            goodSoFar = false;
        
        //Test the first three characters for letters.
        while(goodSoFar && i < 3) 
        {
            if (!Character.isLetter(custID.charAt(i)))
                goodSoFar = false;
            i++;
        }
        
        //Test the last four characters for digits.
        
        while (goodSoFar && i < 7) 
        {
            if (!Character.isDigit(custID.charAt(i)))
                goodSoFar = false;
            i++;
        }
        return goodSoFar;
    }
}