TheAlgorithms/Java · error · IllegalArgumentException

Invalid hexadecimal character: {}

Error message

Invalid hexadecimal character: {}

What it means

Thrown by HexaDecimalToDecimal.getHexaToDec when the input string contains a character not found in the lookup string '0123456789ABCDEF'. The method uppercases the input first, so lowercase a–f are accepted, but any other character (spaces, punctuation, G–Z, special symbols) triggers this error.

Source

Thrown at src/main/java/com/thealgorithms/conversions/HexaDecimalToDecimal.java:38

    }

    /**
     * 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
     */
    public static int getHexaToDec(String hex) {
        String digits = "0123456789ABCDEF";
        hex = hex.toUpperCase();
        int val = 0;

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

        return val;
    }
}

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Sanitize the input: strip whitespace and remove common hex prefixes like '0x' or '#' before calling getHexaToDec.
2. Validate each character against [0-9A-Fa-f] using a regex like ^[0-9A-Fa-f]+$ before conversion.
3. If the input may be empty, check for emptiness first and decide on a default or error.

Example fix

// before
int result = HexaDecimalToDecimal.getHexaToDec(hexInput); // hexInput may be '#FF00FF'

// after
String cleaned = hexInput.replaceAll("^0x|^#", "").trim();
if (!cleaned.matches("^[0-9A-Fa-f]+$")) {
    throw new IllegalArgumentException("Invalid hex string: " + hexInput);
}
int result = HexaDecimalToDecimal.getHexaToDec(cleaned);

String cleaned = hex.replaceAll("^0x|^#", "").trim();
if (!cleaned.matches("^[0-9A-Fa-f]+$")) {
    throw new IllegalArgumentException("Invalid hex string: " + hex);
}
int result = HexaDecimalToDecimal.getHexaToDec(cleaned);

static boolean isValidHex(String s) {
    return s != null && !s.isEmpty() && s.matches("^[0-9A-Fa-f]+$");
}

try {
    int result = HexaDecimalToDecimal.getHexaToDec(hex);
} catch (IllegalArgumentException e) {
    // invalid hex character; log and skip or use default
    logger.warn("Invalid hex input: {}", hex);
}

When it happens

Trigger: Passing a string containing characters outside 0–9 and A–F (case-insensitive), such as 'GG', '12 34', '#FF00FF', or '0x1A'. Passing an empty string produces no character iteration (no error), but whitespace or sign characters like '+' or '-' will trigger it.

Common situations: Reading hex strings from a file or database with formatting characters (e.g., '0x' prefix, spaces, dashes). Accepting user input without stripping whitespace or prefix notation. Copying color hex codes that include a '#' prefix.

Related errors

• Base must be between 2 and 36
• Decimal number cannot be negative.
• Input cannot be null or empty
• Incorrect input: Expecting an octal number (digits 0-7)
• Input cannot be null or empty

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/4be3c97f818a477c. Report an issue: GitHub.