AnyBaseToDecimal.java

package com.thealgorithms.conversions;

/**
 * @author Varun Upadhyay (<a href="https://github.com/varunu28">...</a>)
 */
public final class AnyBaseToDecimal {
 private static final int CHAR_OFFSET_FOR_DIGIT = '0';
 private static final int CHAR_OFFSET_FOR_UPPERCASE = 'A' - 10;

 private AnyBaseToDecimal() {
 }

 /**
 * Convert any radix to a decimal number.
 *
 * @param input the string to be converted
 * @param radix the radix (base) of the input string
 * @return the decimal equivalent of the input string
 * @throws NumberFormatException if the input string or radix is invalid
 */
 public static int convertToDecimal(String input, int radix) {
 int result = 0;
 int power = 1;

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

 /**
 * Convert a character to its integer value.
 *
 * @param character the character to be converted
 * @return the integer value represented by the character
 * @throws NumberFormatException if the character is not an uppercase letter or a digit
 */
 private static int valOfChar(char character) {
 if (Character.isDigit(character)) {
 return character - CHAR_OFFSET_FOR_DIGIT;
 } else if (Character.isUpperCase(character)) {
 return character - CHAR_OFFSET_FOR_UPPERCASE;
 } else {
 throw new NumberFormatException("invalid character:" + character);
 }
 }
}