TheAlgorithms/Java · error · IllegalArgumentException

The number must be in the range [%d, %d]

Error message

The number must be in the range [%d, %d]

What it means

Thrown by RomanNumeralUtil.generate(int) when the input falls outside the supported additive Roman numeral range [1, 5999]. The lookup tables RN_M/RN_C/RN_X/RN_I only cover up to 5999 (MMMMM...), and zero/negative values have no Roman numeral representation, so the guard rejects them before an ArrayIndexOutOfBoundsException or garbage output could occur.

Source

Thrown at src/main/java/com/thealgorithms/maths/RomanNumeralUtil.java:68

        "XC",
    };
    // 1-9
    private static final String[] RN_I = {
        "",
        "I",
        "II",
        "III",
        "IV",
        "V",
        "VI",
        "VII",
        "VIII",
        "IX",
    };

    public static String generate(int number) {
        if (number < MIN_VALUE || number > MAX_VALUE) {
            throw new IllegalArgumentException(String.format("The number must be in the range [%d, %d]", MIN_VALUE, MAX_VALUE));
        }

        return (RN_M[number / 1000] + RN_C[number % 1000 / 100] + RN_X[number % 100 / 10] + RN_I[number % 10]);
    }
}

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Clamp or reject the input before calling generate(), ensuring 1 <= number <= 5999.
2. If you need values >= 6000, switch to a library that supports vinculum (overbar) notation instead of this util.
3. Add a unit test asserting generate(1) and generate(5999) succeed while generate(0) and generate(6000) throw.

Example fix

// before
String r = RomanNumeralUtil.generate(userValue);

// after
if (userValue < 1 || userValue > 5999) {
    throw new IllegalArgumentException("Value out of Roman range: " + userValue);
}
String r = RomanNumeralUtil.generate(userValue);

if (number < 1 || number > 5999) {
    throw new IllegalArgumentException("Value out of Roman range [1,5999]: " + number);
}
String r = RomanNumeralUtil.generate(number);

try {
    String r = RomanNumeralUtil.generate(number);
} catch (IllegalArgumentException e) {
    // surface a user-facing error; do not silently default
    throw new DomainException("Unsupported value for Roman conversion", e);
}

When it happens

Trigger: Call RomanNumeralUtil.generate(0), generate(-1), generate(6000), or generate with any int < 1 or > 5999. Also hit by passing Integer.MAX_VALUE or a parsed user value that overflowed a bound check upstream.

Common situations: Off-by-one loop counters starting at 0, unchecked external input parsed into an int, code that assumed Roman numerals are unbounded, or a refactor that changed the expected domain without updating callers.

Related errors

• Input array must have length of at least two
• numOfTerms nonnegative.
• n must be non-negative.
• Input must be non-negative
• sylvester() does not accept negative numbers or zero.

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/45bce4099476840c. Report an issue: GitHub.