TheAlgorithms/Java · error · IllegalArgumentException

Incorrect octal digit: {}

Error message

Incorrect octal digit: {}

What it means

Thrown by OctalToHexadecimal.octalToDecimal when any character in the input string is outside the octal digit range '0'–'7'. The check uses char comparison (currentChar < '0' || currentChar > '7'), so characters '8', '9', letters, whitespace, signs, or special characters all trigger it. The offending character is included in the error message.

Source

Thrown at src/main/java/com/thealgorithms/conversions/OctalToHexadecimal.java:32

    }

    /**
     * Converts an Octal number (as a string) to its Decimal equivalent.
     *
     * @param octalNumber The Octal number as a string
     * @return The Decimal equivalent of the Octal number
     * @throws IllegalArgumentException if the input contains invalid octal digits
     */
    public static int octalToDecimal(String octalNumber) {
        if (octalNumber == null || octalNumber.isEmpty()) {
            throw new IllegalArgumentException("Input cannot be null or empty");
        }

        int decimalValue = 0;
        for (int i = 0; i < octalNumber.length(); i++) {
            char currentChar = octalNumber.charAt(i);
            if (currentChar < '0' || currentChar > '7') {
                throw new IllegalArgumentException("Incorrect octal digit: " + currentChar);
            }
            int currentDigit = currentChar - '0';
            decimalValue = decimalValue * OCTAL_BASE + currentDigit;
        }

        return decimalValue;
    }

    /**
     * Converts a Decimal number to its Hexadecimal equivalent.
     *
     * @param decimalNumber The Decimal number
     * @return The Hexadecimal equivalent of the Decimal number
     */
    public static String decimalToHexadecimal(int decimalNumber) {
        if (decimalNumber == 0) {
            return "0";
        }

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Validate the input with a regex like ^[0-7]+$ before calling octalToDecimal.
2. Strip any prefixes or whitespace, then re-validate.
3. If the input format is ambiguous, detect it first and route to the correct converter.

Example fix

// before
int decimal = OctalToHexadecimal.octalToDecimal(octalStr);

// after
if (!octalStr.matches("^[0-7]+$")) {
    throw new IllegalArgumentException("Input must contain only octal digits 0-7: " + octalStr);
}
int decimal = OctalToHexadecimal.octalToDecimal(octalStr);

if (!octalNumber.matches("^[0-7]+$")) {
    throw new IllegalArgumentException("Input must contain only octal digits 0-7: " + octalNumber);
}
int result = OctalToHexadecimal.octalToDecimal(octalNumber);

static boolean isValidOctalDigits(String s) {
    return s != null && s.matches("^[0-7]+$");
}

try {
    int result = OctalToHexadecimal.octalToDecimal(octalNumber);
} catch (IllegalArgumentException e) {
    // non-octal character present; route to correct parser or reject
    logger.warn("Invalid octal digit in: {}", octalNumber);
}

When it happens

Trigger: Passing a string containing '8', '9', letters, whitespace, or any non-octal character. Providing input formatted with a prefix like '0o17'. Supplying a decimal or hex string to the octal converter by mistake.

Common situations: A data pipeline routes mixed-format numeric strings to the octal converter. User input is not validated before conversion. File permission representations contain unexpected characters.

Related errors

• 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
• Base must be between 2 and 36

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/cb4951d6d99bfe89. Report an issue: GitHub.