TheAlgorithms/Java · error · IllegalArgumentException

The number must be in the range

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.

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
• Input must be non-negative
• n must be non-negative.
• numOfTerms nonnegative.
• 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.

Appendix: 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]);
    }
}

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