public class DigitExtractor
{
	public DigitExtractor(String code)
	{
		isbn = code;
	}
	public int nextDigit()
	{
		// convert to int
		digit = isbn.charAt(count) - 48;
 
		count += 1;
 
		return digit;
	}
	public int getLength()
	{
		return isbn.length();
	}
	public String getISBN()
	{
		return isbn;
	}
	private String isbn;
	private int digit;
	private int count;
}

public class ISBNChecker
{
	public static void main(String[] args)
	{
		DigitExtractor myDigit = new DigitExtractor("123456789X");
		int sum = 0;		// holds the sum
		int rem = 0;		// holds the remainder
		int checkSum = 0;	// holds the checkSum value
 
		if (myDigit.getLength() == 10)
		{
			// extract the next digit and add it to the sum
			for (int cnt = 0; cnt < myDigit.getLength() - 1; cnt++)
			{
				int temp = myDigit.nextDigit() * (myDigit.getLength() - cnt);
				sum += temp;
				System.out.println(temp);
			}
 
			System.out.println("sum: " + sum);
 
			// get the remainder of sum / 11
			rem = sum % 11;
			System.out.println("remainder: " + rem);
 
			// subtract remainder from 11 to get checkSum
			checkSum = 11 - rem;
 
			System.out.println("checksum: " + checkSum);
		}
		else if (myDigit.getLength() == 13)
		{
			// extract the next digit and add it to the sum
			for (int cnt = 0; cnt < myDigit.getLength() - 1; cnt++)
			{
				int temp = myDigit.nextDigit();
 
				if ((cnt + 1) % 2 == 0)
				{
					sum += temp * 3;
					System.out.println(temp * 3);
				}
				else
				{
					sum += temp;
					System.out.println(temp);
				}
			}
 
			System.out.println("sum: " + sum);
			// get the remainder of sum/10
			rem = sum % 10;
			System.out.println("rem: " + rem);
 
			// subtract remainder from 10 to get checkSum
			checkSum = 10 - rem;
 
			System.out.println("checksum: " + checkSum);
		}
		else
			System.out.println("Invalid ISBN");
 
		// check the sum to see if it is valid
		if (checkSum < 10 && (myDigit.getISBN().charAt(myDigit.getLength() - 1) == (checkSum + 48)))
			System.out.println("Valid ISBN - num");
		else if (checkSum >= 10 && (myDigit.getISBN().charAt(myDigit.getLength() - 1) == 'X'))
			System.out.println("Valid ISBN - X");
		else
			System.out.println("Invalid ISBN");
	}
}