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package org.hsqldb.lib;

/**
 * Provides the base HSQLDB interface for Heap ADT implementations. <p>
 *
 * In this context, a Heap is simply a collection-like ADT that allows addition
 * of elements and provides a way to remove the least element, given some
 * implementation-dependent strategy for imposing an order over its
 * elements. <p>
 *
 * Typically, an HsqlHeap will be implemented as a tree-like structure that
 * recursively guarantees a <i>Heap Invariant</i>, such that all nodes below
 * the root are greater than the root, given some comparison strategy. <p>

 * This in turn provides the basis for an efficient implementation of ADTs such
 * PriorityQueue, since Heap operations using the typical implementation are,
 * in theory, guaranteed to be O(log n).
 *
 * @author Campbell Burnet (campbell-burnet@users dot sourceforge.net)
 * @version 1.7.2
 * @since 1.7.2
 */
public interface HsqlHeap {

    /**
     * Removes all of the elements from this Heap.
     */
    void clear();

    /**
     * Retrieves whether this Heap is empty.
     */
    boolean isEmpty();

    /**
     * Retrieves whether this Heap is full.
     */
    boolean isFull();

    /**
     * Adds the specified element to this Heap.
     *
     * @param o The element to add
     * @throws IllegalArgumentException if the implementation does
     *      not accept elements of the supplied type (optional)
     * throws RuntimeException if the implementation
     *      dictates that this Heap is not currently accepting additions
     *      or that this Heap is currently full (optional)
     */
    void add(Object o) throws IllegalArgumentException, RuntimeException;

    /**
     * Retrieves the least element from this Heap, without removing it.
     *
     * @return the least element from this Heap
     */
    Object peek();

    /**
     * Retrieves the least element from this Heap, removing it in the process.
     *
     * @return the least element from this Heap
     */
    Object remove();

    /**
     * Retrieves the number of elements currently in this Heap.
     *
     * @return the number of elements currently in this Heap
     */
    int size();
}
