TheAlgorithms/Java · error · IllegalArgumentException

Capacity cannot be negative.

Error message

Capacity cannot be negative.

What it means

The DynamicArray constructor rejects negative capacity because the backing Object[] array cannot have a negative length. Java would throw an obscure NegativeArraySizeException otherwise; this guard provides a clearer, catchable IllegalArgumentException. A capacity of 0 is permitted (creates an empty backing array that grows on demand).

Source

Thrown at src/main/java/com/thealgorithms/datastructures/dynamicarray/DynamicArray.java:35

 *
 * @param <E> the type of elements that this array can hold
 */
public class DynamicArray<E> implements Iterable<E> {

    private static final int DEFAULT_CAPACITY = 16;
    private int size;
    private int modCount; // Tracks structural modifications for iterator integrity
    private Object[] elements;

    /**
     * Constructs a new DynamicArray with the specified initial capacity.
     *
     * @param capacity the initial capacity of the array
     * @throws IllegalArgumentException if the specified capacity is negative
     */
    public DynamicArray(final int capacity) {
        if (capacity < 0) {
            throw new IllegalArgumentException("Capacity cannot be negative.");
        }
        this.size = 0;
        this.modCount = 0;
        this.elements = new Object[capacity];
    }

    /**
     * Constructs a new DynamicArray with a default initial capacity.
     */
    public DynamicArray() {
        this(DEFAULT_CAPACITY);
    }

    /**
     * Adds an element to the end of the array. If the array is full, it
     * creates a new array with double the size to accommodate the new element.
     *
     * @param element the element to be added to the array

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Validate that capacity >= 0 before constructing
2. Use the no-arg constructor (defaults to capacity 16) when you do not have a specific size requirement
3. Clamp to 0 if negative capacity is possible from the computation

Example fix

// before
DynamicArray<String> arr = new DynamicArray<>(requestedSize - buffer);

// after
int cap = Math.max(0, requestedSize - buffer);
DynamicArray<String> arr = new DynamicArray<>(cap);

int cap = Math.max(0, requestedCapacity);
DynamicArray<String> arr = new DynamicArray<>(cap);

try {
    arr = new DynamicArray<>(capacity);
} catch (IllegalArgumentException e) {
    arr = new DynamicArray<>(); // default capacity 16
}

When it happens

Trigger: Calling new DynamicArray<>(-1) or passing any negative int to the constructor. Can also arise from arithmetic that produces a negative result.

Common situations: Capacity derived from a subtraction or a computed size that goes negative on edge cases. Config values or user input passed through without validation.

Related errors

• capacity must greater than 0!
• Capacity must be greater than 0!
• Index cannot be negative.
• initialCapacity < 1
• Denominator cannot be 0

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/b2099ba301cccb5a. Report an issue: GitHub.