HexaDecimalToDecimal.java

packagecom.thealgorithms.conversions;

/**
 * Utility class for converting a hexadecimal string to its decimal representation.
 * <p>
 * A hexadecimal number uses the base-16 numeral system, with the following characters:
 * <ul>
 * <li>Digits: 0-9</li>
 * <li>Letters: A-F (case-insensitive)</li>
 * </ul>
 * Each character represents a power of 16. For example:
 * <pre>
 * Hexadecimal "A1" = 10*16^1 + 1*16^0 = 161 (decimal)
 * </pre>
 *
 * <p>This class provides a method to perform the conversion without using built-in Java utilities.</p>
 */
publicfinalclassHexaDecimalToDecimal {
privateHexaDecimalToDecimal() {
 }

/**
 * Converts a hexadecimal string to its decimal integer equivalent.
 * <p>The input string is case-insensitive, and must contain valid hexadecimal characters [0-9, A-F].</p>
 *
 * @param hex the hexadecimal string to convert
 * @return the decimal integer representation of the input hexadecimal string
 * @throws IllegalArgumentException if the input string contains invalid characters
 */
publicstaticintgetHexaToDec(Stringhex) {
Stringdigits = "0123456789ABCDEF";
hex = hex.toUpperCase();
intval = 0;

for (inti = 0; i < hex.length(); i++) {
intd = digits.indexOf(hex.charAt(i));
if (d == -1) {
thrownewIllegalArgumentException("Invalid hexadecimal character: " + hex.charAt(i));
 }
val = 16 * val + d;
 }

returnval;
 }
}