TheAlgorithms/Java · error · IllegalArgumentException

Values and weights arrays must not be null.

Error message

Values and weights arrays must not be null.

What it means

KnapsackZeroOneTabulation.compute allocates a 2D DP table and indexes both arrays by item index. It rejects null values or weights arrays with IllegalArgumentException to prevent an NPE during table population.

Source

Thrown at src/main/java/com/thealgorithms/dynamicprogramming/KnapsackZeroOneTabulation.java:38

 */
public final class KnapsackZeroOneTabulation {

    private KnapsackZeroOneTabulation() {
        // Prevent instantiation
    }

    /**
     * Solves the 0-1 Knapsack problem using the bottom-up tabulation technique.
     * @param values the values of the items
     * @param weights the weights of the items
     * @param capacity the total capacity of the knapsack
     * @param itemCount the number of items
     * @return the maximum value that can be put in the knapsack
     * @throws IllegalArgumentException if input arrays are null, of different lengths,or if capacity or itemCount is invalid
     */
    public static int compute(final int[] values, final int[] weights, final int capacity, final int itemCount) {
        if (values == null || weights == null) {
            throw new IllegalArgumentException("Values and weights arrays must not be null.");
        }
        if (values.length != weights.length) {
            throw new IllegalArgumentException("Values and weights arrays must be non-null and of same length.");
        }
        if (capacity < 0) {
            throw new IllegalArgumentException("Capacity must not be negative.");
        }
        if (itemCount < 0 || itemCount > values.length) {
            throw new IllegalArgumentException("Item count must be between 0 and the length of the values array.");
        }

        final int[][] dp = new int[itemCount + 1][capacity + 1];

        for (int i = 1; i <= itemCount; i++) {
            final int currentValue = values[i - 1];
            final int currentWeight = weights[i - 1];

            for (int w = 1; w <= capacity; w++) {

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Default array fields to new int[0] instead of null.
2. Guard with Objects.requireNonNull at the call boundary.
3. If null means 'no items', return 0 early instead of calling compute.

Example fix

// before
int r = KnapsackZeroOneTabulation.compute(values, null, cap, count); // throws

// after
int[] w = Objects.requireNonNullElseGet(weights, () -> new int[0]);
int r = KnapsackZeroOneTabulation.compute(values, w, cap, Math.min(count, w.length));

if (values == null || weights == null) {
    throw new IllegalArgumentException("Arrays must not be null");
}
int r = KnapsackZeroOneTabulation.compute(values, weights, capacity, itemCount);

static boolean areNonNullArrays(int[] values, int[] weights) {
    return values != null && weights != null;
}

When it happens

Trigger: Calling compute(values, weights, capacity, itemCount) where values or weights is null — from uninitialized fields, failed JSON deserialization, or optional parameters left null.

Common situations: Deserialized request objects with nullable array fields; test fixtures that omit one array; legacy code using null to mean 'no items' instead of an empty array.

Related errors

• Weights and values must be non-null and of the same length.
• Input arrays cannot be null.
• Cannot enqueue null data
• Cannot enqueue null item.
• Input strings must not be null.

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/8ff46d370d4d4801. Report an issue: GitHub.