TheAlgorithms/Java · error · IllegalArgumentException

Empty list given for Mean computation.

Error message

Empty list given for Mean computation.

What it means

Thrown by the private checkIfNotEmpty(Iterable<Double>) method, invoked by arithmetic(), geometric(), harmonic(), and quadratic(). All four mean computations require at least one element to divide by; an empty iterable would cause a division by zero or undefined average. The check uses numbers.iterator().hasNext() to detect emptiness.

Solutions

1. Check that the iterable has at least one element before calling any Means method
2. Handle the empty case explicitly (return a default, skip, or log) rather than passing it to the mean
3. Use collection.isEmpty() or !iterator().hasNext() as a pre-check

Example fix

// before
Double mean = Means.arithmetic(filteredNumbers);

// after
if (filteredNumbers == null || !filteredNumbers.iterator().hasNext()) {
    return Optional.empty();  // or throw a domain-specific exception
}
Double mean = Means.arithmetic(filteredNumbers);

if (numbers == null || !numbers.iterator().hasNext()) {
    return Optional.<Double>empty();
}
Double mean = Means.arithmetic(numbers);

static boolean hasElements(Iterable<?> iterable) {
    return iterable != null && iterable.iterator().hasNext();
}

try {
    Double mean = Means.arithmetic(numbers);
} catch (IllegalArgumentException e) {
    // input was empty — return default or skip
    return Optional.empty();
}

When it happens

Trigger: Calling Means.arithmetic(emptyList), Means.geometric(Collections.emptyList()), or any mean method with an empty Collection, Set, or custom Iterable. Note: passing null would cause a NullPointerException before this check, not this error.

Common situations: Filtering a collection to compute a mean, where the filter removes all elements. Reading from an empty database query result or empty stream-into-list. Edge case in data pipelines where some partitions have no data.

Related errors

• Values array cannot be empty or null
• Base must be greater than 1.
• Input arrays cannot be empty.
• Input must be a positive integer. Provided:
• Input must be non-negative. Received:

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/b987e0452fd9b6bd. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/com/thealgorithms/maths/Means.java:140

     * @see <a href="https://en.wikipedia.org/wiki/Root_mean_square">Quadratic
     *      Mean</a>
     */
    public static Double quadratic(final Iterable<Double> numbers) {
        checkIfNotEmpty(numbers);
        double sumOfSquares = StreamSupport.stream(numbers.spliterator(), false).reduce(0d, (x, y) -> x + y * y);
        int size = IterableUtils.size(numbers);
        return Math.pow(sumOfSquares / size, 0.5);
    }

    /**
     * Validates that the input iterable is not empty.
     *
     * @param numbers the input numbers to validate
     * @throws IllegalArgumentException if the input is empty
     */
    private static void checkIfNotEmpty(final Iterable<Double> numbers) {
        if (!numbers.iterator().hasNext()) {
            throw new IllegalArgumentException("Empty list given for Mean computation.");
        }
    }
}

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