TheAlgorithms/Java · error · IllegalArgumentException

initialCapacity < 1

Error message

initialCapacity < 1

What it means

Thrown by the IndexedPriorityQueue(int initialCapacity, Comparator) constructor when initialCapacity is less than 1. The constructor immediately allocates `new Object[initialCapacity]`, so a zero or negative value would yield an unusable or malformed backing array. The no-arg and Comparator-only constructors default to 11 to avoid this.

Source

Thrown at src/main/java/com/thealgorithms/datastructures/heaps/IndexedPriorityQueue.java:77

     * </ul>
     * If you prefer value-based semantics, replace with HashMap<E,Integer> and
     * respect the warnings in the class Javadoc.
     */
    private final IdentityHashMap<E, Integer> index;

    private static final int DEFAULT_INITIAL_CAPACITY = 11;

    public IndexedPriorityQueue() {
        this(DEFAULT_INITIAL_CAPACITY, null);
    }

    public IndexedPriorityQueue(Comparator<? super E> cmp) {
        this(DEFAULT_INITIAL_CAPACITY, cmp);
    }

    public IndexedPriorityQueue(int initialCapacity, Comparator<? super E> cmp) {
        if (initialCapacity < 1) {
            throw new IllegalArgumentException("initialCapacity < 1");
        }
        this.heap = new Object[initialCapacity];
        this.cmp = cmp;
        this.index = new IdentityHashMap<>();
    }

    /** Returns current number of elements. */
    public int size() {
        return size;
    }

    /** Returns {@code true} if empty. */
    public boolean isEmpty() {
        return size == 0;
    }

    /**
     * Returns the minimum element without removing it, or {@code null} if empty.

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Pass a value >= 1, or use the no-arg / Comparator-only constructor to get the default capacity of 11.
2. Clamp externally sourced capacity: `Math.max(1, configuredCapacity)` before constructing.
3. Validate configuration at load time and fail fast with a clear config error rather than at PQ construction.

Example fix

// before
new IndexedPriorityQueue<>(config.getCapacity(), cmp);

// after
int cap = Math.max(1, config.getCapacity());
new IndexedPriorityQueue<>(cap, cmp);

int cap = Math.max(1, configuredCapacity);
new IndexedPriorityQueue<>(cap, cmp);

When it happens

Trigger: Passing 0 explicitly; passing a negative number; computing capacity as `collection.size()` on an empty collection; wiring a config property that defaults to 0.

Common situations: Capacity read from a properties/YAML file with no default; sizing math with an off-by-one (`size - 1`); DI/bean configuration supplying an unset int field.

Related errors

• Queue is full
• capacity must greater than 0!
• Capacity must be greater than 0!
• Capacity cannot be negative.
• Element not in queue

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/8458ee3dd60d2609. Report an issue: GitHub.