/**
   * The default initial capacity - MUST be a power of two.
   **/
  static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16

  /**
   * The maximum capacity, used if a higher value is implicitly specified
   * by either of the constructors with arguments.
   * MUST be a power of two <= 1<<30.
   **/
  static final int MAXIMUM_CAPACITY = 1 << 30;

  /**
   * The load factor used when none specified in constructor.
   **/
  static final float DEFAULT_LOAD_FACTOR = 0.75f;

  /**
   * The bin count threshold for using a tree rather than list for a
   * bin. Bins are converted to trees when adding an element to a
   * bin with at least this many nodes. The value must be greater
   * than 2 and should be at least 8 to mesh with assumptions in
   * tree removal about conversion back to plain bins upon
   * shrinkage.
   **/
  static final int TREEIFY_THRESHOLD = 8;
  /**
   * The bin count threshold for untreeifying a (split) bin during a
   * resize operation. Should be less than TREEIFY_THRESHOLD, and at
   * most 6 to mesh with shrinkage detection under removal.
   **/
  static final int UNTREEIFY_THRESHOLD = 6;
  /**
   * The smallest table capacity for which bins may be treeified.
   * (Otherwise the table is resized if too many nodes in a bin.)
   * Should be at least 4 * TREEIFY_THRESHOLD to avoid conflicts
   * between resizing and treeification thresholds.
   **/
  static final int MIN_TREEIFY_CAPACITY = 64;

  /**
   * The table, initialized on first use, and resized as
   * necessary. When allocated, length is always a power of two.
   * (We also tolerate length zero in some operations to allow
   * bootstrapping mechanics that are currently not needed.)
   **/
  transient Node<K,V>[] table;

  /**
   * Holds cached entrySet(). Note that AbstractMap fields are used
   * for keySet() and values().
   **/
  transient Set<Map.Entry<K,V>> entrySet;

  /**
   * The number of key-value mappings contained in this map.
   **/
  transient int size;
  /**
   * The number of times this HashMap has been structurally modified
   * Structural modifications are those that change the number of mappings in
   * the HashMap or otherwise modify its internal structure (e.g.,
   * rehash). This field is used to make iterators on Collection-views of
   * the HashMap fail-fast. (See ConcurrentModificationException).
   **/
  transient int modCount;
  /**
   * The next size value at which to resize (capacity * load factor).
   * @serial
   **/
  // (The javadoc description is true upon serialization.
  // Additionally, if the table array has not been allocated, this
  // field holds the initial array capacity, or zero signifying
  // DEFAULT_INITIAL_CAPACITY.)
  int threshold;
  /**
   * The load factor for the hash table.
   *
   * @serial
   **/
  final float loadFactor;