TheAlgorithms/Java · error · IllegalArgumentException

n must be non-negative.

Error message

n must be non-negative.

What it means

Thrown by SumOfOddNumbers.sumOfFirstNOddNumbers when n is negative. The method returns n*n (the identity that the sum of the first n odd numbers equals n^2), which is only meaningful for n >= 0; a negative count of 'first N odd numbers' is undefined.

Source

Thrown at src/main/java/com/thealgorithms/maths/SumOfOddNumbers.java:21

/**
 * This program calculates the sum of the first n odd numbers.
 *
 * https://www.cuemath.com/algebra/sum-of-odd-numbers/
 */

public final class SumOfOddNumbers {
    private SumOfOddNumbers() {
    }

    /**
     * Calculate sum of the first n odd numbers
     *
     * @param n the number of odd numbers to sum
     * @return sum of the first n odd numbers
     */
    public static int sumOfFirstNOddNumbers(final int n) {
        if (n < 0) {
            throw new IllegalArgumentException("n must be non-negative.");
        }
        return n * n;
    }
}

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Validate n >= 0 at the call site before invoking.
2. Use Math.max(0, n) when a negative should silently map to 0.
3. Sanitize the source of n (e.g., parsed CLI argument or HTTP parameter).

Example fix

// before
int s = SumOfOddNumbers.sumOfFirstNOddNumbers(n);

// after
int s = SumOfOddNumbers.sumOfFirstNOddNumbers(Math.max(0, n));

if (n < 0) throw new IllegalArgumentException("n must be >= 0");
int s = SumOfOddNumbers.sumOfFirstNOddNumbers(n);

When it happens

Trigger: Call sumOfFirstNOddNumbers(-1) or pass a count derived from user input or a size computation that underflowed.

Common situations: Parsing a user-supplied count without validation, off-by-one in loop bounds, or an empty collection whose size was decremented.

Related errors

• The number must be in the range [%d, %d]
• Input array must have length of at least two
• numOfTerms nonnegative.
• 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/dfaa27f8c4327234. Report an issue: GitHub.