TheAlgorithms/Java · error · IllegalArgumentException

The input array cannot be null

Error message

The input array cannot be null

What it means

Thrown by BitonicSort.sort(T[]) when array == null. Bitonic sort pads the array to the next power of two and then compares elements, both of which dereference the array reference. The guard converts a latent NullPointerException into a descriptive IllegalArgumentException before any processing.

Source

Thrown at src/main/java/com/thealgorithms/sorts/BitonicSort.java:25

 * BitonicSort class implements the SortAlgorithm interface using the bitonic sort technique.
 */
public class BitonicSort implements SortAlgorithm {
    private enum Direction {
        DESCENDING,
        ASCENDING,
    }

    /**
     * Sorts the given array using the Bitonic Sort algorithm.
     *
     * @param <T> the type of elements in the array, which must implement the Comparable interface
     * @param array the array to be sorted
     * @return the sorted array
     */
    @Override
    public <T extends Comparable<T>> T[] sort(T[] array) {
        if (array == null) {
            throw new IllegalArgumentException("The input array cannot be null");
        }
        if (array.length == 0) {
            return array;
        }

        final int paddedSize = nextPowerOfTwo(array.length);
        T[] paddedArray = Arrays.copyOf(array, paddedSize);

        // Fill the padded part with a maximum value
        final T maxValue = max(array);
        Arrays.fill(paddedArray, array.length, paddedSize, maxValue);

        bitonicSort(paddedArray, 0, paddedSize, Direction.ASCENDING);
        return Arrays.copyOf(paddedArray, array.length);
    }

    private <T extends Comparable<T>> void bitonicSort(final T[] array, final int low, final int cnt, final Direction direction) {
        if (cnt > 1) {

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Null-check the array before calling sort() and return an empty array or skip.
2. Initialize collections/arrays to empty rather than null.
3. Annotate the parameter @NonNull and enable static analysis.

Example fix

// before
T[] sorted = new BitonicSort().sort(arr);

// after
if (arr == null) throw new IllegalArgumentException("arr must not be null");
T[] sorted = new BitonicSort().sort(arr);

if (array == null) throw new IllegalArgumentException("array must not be null");

public static <T> boolean isSortable(T[] array) { return array != null; }

When it happens

Trigger: Calling sort(null); passing a reference initialized to null; forwarding a value from a Map.get() that returned null.

Common situations: Uninitialized fields; data loaders returning null on missing input; null used as a sentinel for 'no data'.

Related errors

• Input array must not be null.
• Key must not be null.
• Array cannot be null
• IPv4 address is empty.
• Input cannot be null or empty

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/753c180590b8a327. Report an issue: GitHub.