TheAlgorithms/Java · error · IllegalArgumentException

Target must be non-negative

Error message

Target must be non-negative

What it means

Thrown by DiceThrower.getDiceCombinations(target) when target < 0. The recursion subtracts dice faces (1-6) from the remaining sum toward a base case of 0, so a negative target has no valid combination of positive faces. target == 0 returns a single empty combination.

Source

Thrown at src/main/java/com/thealgorithms/recursion/DiceThrower.java:35

 *
 * @author BEASTSHRIRAM
 * @see <a href="https://en.wikipedia.org/wiki/Backtracking">Backtracking Algorithm</a>
 */
public final class DiceThrower {

    private DiceThrower() {
        // Utility class
    }

    /**
     * Returns all possible dice roll combinations that sum to the target
     *
     * @param target the target sum to achieve with dice rolls
     * @return list of all possible combinations as strings
     */
    public static List<String> getDiceCombinations(int target) {
        if (target < 0) {
            throw new IllegalArgumentException("Target must be non-negative");
        }
        return generateCombinations("", target);
    }

    /**
     * Prints all possible dice roll combinations that sum to the target
     *
     * @param target the target sum to achieve with dice rolls
     */
    public static void printDiceCombinations(int target) {
        if (target < 0) {
            throw new IllegalArgumentException("Target must be non-negative");
        }
        printCombinations("", target);
    }

    /**
     * Recursive helper method to generate all combinations

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Validate target >= 0 at the caller and reject early.
2. If target can legitimately be 0 or small, let it through (0 returns an empty-string combination).
3. Guard against very large targets too — this enumerates ALL compositions of target with parts 1-6, which grows exponentially and can hang/OOM.

Example fix

// before
List<String> c = DiceThrower.getDiceCombinations(target); // target may be negative

// after
if (target < 0) throw new IllegalArgumentException("target must be >= 0");
List<String> c = DiceThrower.getDiceCombinations(target);

if (target < 0) {
    throw new IllegalArgumentException("target must be >= 0");
}
List<String> c = DiceThrower.getDiceCombinations(target);

static boolean validDiceTarget(int t) {
    return t >= 0;
}

try {
    List<String> c = DiceThrower.getDiceCombinations(target);
} catch (IllegalArgumentException e) {
    logger.warn("Negative dice target: {}", target);
}

When it happens

Trigger: Call getDiceCombinations(-1) or any negative target. Note only negativity is rejected; target 0 is valid (returns [""]).

Common situations: Computing target as a difference that went negative; subtracting a bonus from a small target; parsing user input without range checking.

Related errors

• Number of discs must be non-negative
• number is negative
• n must be a non-negative integer
• Input must be non-negative. Received:
• Input must be a positive integer. Provided:

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/d8621476d9b60241. Report an issue: GitHub.