Chapter 12 Exercise 7, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

12.7 (NumberFormatException)
Write the bin2Dec(String binaryString)
method to convert a binary string into a decimal number.
Implement the bin2Dec method to throw a NumberFormatException
if the string is not a binary string.

public class Exercise_07 {

    public static void main(String[] args) {

        System.out.println(bin2Dec("1100100"));
        // Purposely throwing an exception...
        System.out.println(bin2Dec("lafkja"));
    }

    public static int bin2Dec(String binary) throws NumberFormatException {

        if (!isBinary(binary)) {
            throw new NumberFormatException(binary + " is not a binary number.");
        }
        int power = 0;
        int decimal = 0;
        for (int i = binary.length() - 1; i >= 0; i--) {

            if (binary.charAt(i) == '1') {
                decimal += Math.pow(2, power);
            }
            power++;
        }
        return decimal;
    }

    public static boolean isBinary(String binary) {

        for (char ch : binary.toCharArray()) {
            if (ch != '1' && ch != '0') return false;
        }
        return true;
    }
}