//tests a customer number to verify that it is in the proper format
//can also use regular expression to check, refer to java.util.regex package, not covered here

import javax.swing.JOptionPane;

public class eg20_CustomerNumber 
{
	public static void main(String[] args)
	{
		String input; 
	
		//get a customer number
		input = JOptionPane.showInputDialog("Enter a customer number in the form LLLNNNN\n (LLL = letters and NNN = numbers)");
		
		if (isValid(input))  //static method defined below
		{
			JOptionPane.showMessageDialog(null, "That's a valid customer number.");
		} else
		{
			JOptionPane.showMessageDialog(null, "That is not the proper format of a customer number.\n Here is an example: ABC1234");
		}
		
	}
	
	
	private static boolean isValid(String custNumber)
	{
		boolean goodSoFar = true; //flag
		int i=0;
		
		//explain logic here
		//test the length
		if (custNumber.length() !=7)
			goodSoFar = false;
		//first 3 characters for letters
		while (goodSoFar && i<3)
		{
			if (!Character.isLetter(custNumber.charAt(i)))
				goodSoFar = false;
			System.out.println(custNumber.charAt(i)+" => "+goodSoFar);
			i++;
		}
		//last four characters for digits
		while (goodSoFar && i<7)
		{
			if (!Character.isDigit(custNumber.charAt(i)))
				goodSoFar = false;
			System.out.println(custNumber.charAt(i)+" => "+goodSoFar);
			i++;
		}
		
		
		return goodSoFar;
	}
}