AnyBaseToDecimal.java

package Conversions;

/**
 * @author Varun Upadhyay (https://github.com/varunu28)
 */

// Driver program
public class AnyBaseToDecimal {
    public static void main(String[] args) {
        assert convertToDecimal("1010", 2) == Integer.valueOf("1010", 2);
        assert convertToDecimal("777", 8) == Integer.valueOf("777", 8);
        assert convertToDecimal("999", 10) == Integer.valueOf("999", 10);
        assert convertToDecimal("ABCDEF", 16) == Integer.valueOf("ABCDEF", 16);
        assert convertToDecimal("XYZ", 36) == Integer.valueOf("XYZ", 36);
    }

    /**
     * Convert any radix to decimal number
     *
     * @param s     the string to be convert
     * @param radix the radix
     * @return decimal of bits
     * @throws NumberFormatException if {@code bits} or {@code radix} is invalid
     */
    public static int convertToDecimal(String s, int radix) {
        int num = 0;
        int pow = 1;

        for (int i = s.length() - 1; i >= 0; i--) {
            int digit = valOfChar(s.charAt(i));
            if (digit >= radix) {
                throw new NumberFormatException("For input string " + s);
            }
            num += valOfChar(s.charAt(i)) * pow;
            pow *= radix;
        }
        return num;
    }

    /**
     * Convert character to integer
     *
     * @param c the character
     * @return represented digit of given character
     * @throws NumberFormatException if {@code ch} is not UpperCase or Digit character.
     */
    public static int valOfChar(char c) {
        if (!(Character.isUpperCase(c) || Character.isDigit(c))) {
            throw new NumberFormatException("invalid character :" + c);
        }
        return Character.isDigit(c) ? c - '0' : c - 'A' + 10;
    }
}