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SirixDB is a hybrid on-disk and in-memory document oriented, versioned database system. It has a lightweight buffer manager, stores everything in a huge persistent and durable tree and allows efficient reconstruction of every revision. Furthermore, SirixDB implements change tracking, diffing and supports time travel queries.

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package io.sirix.utils;

import java.util.*;
import java.util.function.Supplier;
import java.util.stream.Collectors;

/**
 * This is an efficient and memory-saving hash map for storing primitive integers
 * and objects. It extends the {@link IntSet} class.
 *
 * @param  generic value type
 * @author BaseX Team 2005-22, BSD License
 * @author Christian Gruen
 */
public final class IntObjMap extends IntSet {
  /**
   * Values.
   */
  private Object[] values;

  /**
   * Default constructor.
   */
  public IntObjMap() {
    values = new Object[capacity()];
  }

  /**
   * Default constructor.
   */
  public IntObjMap(int capacity) {
    super(capacity);
    values = new Object[capacity()];
  }

  /**
   * Indexes the specified key and stores the associated value.
   * If the key already exists, the value is updated.
   *
   * @param key   key
   * @param value value
   * @return old value
   */
  @SuppressWarnings("unchecked")
  public E put(final int key, final E value) {
    // array bounds are checked before array is resized..
    final int i = put(key);
    final Object v = values[i];
    values[i] = value;
    return (E) v;
  }

  /**
   * Returns the value for the specified key.
   * Creates a new value if none exists.
   *
   * @param key  key
   * @param func function that create a new value
   * @return value
   */
  public E computeIfAbsent(final int key, final Supplier func) {
    E value = get(key);
    if (value == null) {
      value = func.get();
      put(key, value);
    }
    return value;
  }

  /**
   * Returns the value for the specified key.
   *
   * @param key key to be looked up
   * @return value or {@code null} if the key was not found
   */
  @SuppressWarnings("unchecked")
  public E get(final int key) {
    return (E) values[id(key)];
  }

  /**
   * Returns a value iterator.
   *
   * @return iterator
   */
  public Iterable values() {
    return new ArrayIterator<>(values, 1, size);
  }

  public Collection keys() {
    return Arrays.stream(keys).boxed().collect(Collectors.toList());
  }

  public int[] keyArray() {
    return keys;
  }

  @Override
  protected void rehash(final int newSize) {
    super.rehash(newSize);
    values = Array.copy(values, new Object[newSize]);
  }

  @Override
  public void clear() {
    super.clear();
    Arrays.fill(values, null);
  }

  @Override
  public String toString() {
    final List