TheAlgorithms/Java · error · IllegalArgumentException

Year must be between 46 and 8499.

Error message

Year must be between 46 and 8499.

What it means

Thrown by ZellersCongruence.parsePart (called for the year substring, positions 6-10) when the parsed year is < 46 or > 8499. This range is the algorithmic validity window for Zeller's congruence as implemented here (the constants/rounding in the formula are tuned for that span); years outside it would yield incorrect weekday results, so they are rejected rather than returning wrong answers.

Source

Thrown at src/main/java/com/thealgorithms/maths/ZellersCongruence.java:88

        return "The date " + input + " falls on a " + DAYS[correctedDay] + ".";
    }

    /**
     * Parses a part of the date string and validates its range.
     *
     * @param part  the substring to parse
     * @param min   the minimum valid value
     * @param max   the maximum valid value
     * @param error the error message to throw if validation fails
     * @return the parsed integer value
     * @throws IllegalArgumentException if the part is not a valid number or is out of range
     */
    private static int parsePart(String part, int min, int max, String error) {
        try {
            int value = Integer.parseInt(part);
            if (value < min || value > max) {
                throw new IllegalArgumentException(error);
            }
            return value;
        } catch (NumberFormatException e) {
            throw new IllegalArgumentException("Invalid numeric part: " + part, e);
        }
    }

    /**
     * Validates the separator character in the date string.
     *
     * @param sep the separator character
     * @throws IllegalArgumentException if the separator is not '-' or '/'
     */
    private static void validateSeparator(char sep) {
        if (sep != '-' && sep != '/') {
            throw new IllegalArgumentException("Date separator must be '-' or '/'.");
        }
    }

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Constrain the year to [46, 8499] at the call site and surface the limit to users.
2. For 2-digit year input, apply a pivot (e.g., +2000) before formatting.
3. If you need dates outside the window, use java.time LocalDate directly instead of this util.

Example fix

// before
String input = String.format("%02d-%02d-%04d", m, d, twoDigitYear);

// after
int fullYear = twoDigitYear + 2000; // or your pivot
String input = String.format("%02d-%02d-%04d", m, d, fullYear);

if (year < 46 || year > 8499) throw new IllegalArgumentException("year out of [46,8499]");
String input = String.format("%02d-%02d-%04d", month, day, year);
String d = ZellersCongruence.calculateDay(input);

When it happens

Trigger: Call calculateDay("01-01-0001"), calculateDay("01-01-9000"), or any 4-digit year field outside [46, 8499].

Common situations: Two-digit years expanded incorrectly (e.g., '22' -> 22 instead of 2022), ancient-history or far-future dates, or test fixtures with year 1.

Related errors

• Month must be between 1 and 12.
• Day must be between 1 and 31.
• Input date must be 10 characters long in the format MM-DD-YY
• Invalid date.
• Bit positions must be between 0 and 31

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/14fbc8b8e44ba599. Report an issue: GitHub.