Java源码解析HashMap的resize函数

  /**   * Initializes or doubles table size. If null, allocates in   * accord with initial capacity target held in field threshold.   * Otherwise, because we are using power-of-two expansion, the   * elements from each bin must either stay at same index, or move   * with a power of two offset in the new table.   * @return the table   **/

  final Node<K,V>[] resize() {    Node<K,V>[] oldTab = table;    int oldCap = (oldTab == null) ? 0 : oldTab.length;    int oldThr = threshold;    int newCap, newThr = 0;    if (oldCap > 0) {      if (oldCap >= MAXIMUM_CAPACITY) {        threshold = Integer.MAX_VALUE;        return oldTab;      }      else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&           oldCap >= DEFAULT_INITIAL_CAPACITY)        newThr = oldThr << 1; // double threshold    }    else if (oldThr > 0) // initial capacity was placed in threshold      newCap = oldThr;    else {        // zero initial threshold signifies using defaults      newCap = DEFAULT_INITIAL_CAPACITY;      newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);    }    if (newThr == 0) {      float ft = (float)newCap * loadFactor;      newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?           (int)ft : Integer.MAX_VALUE);    }    threshold = newThr;    @SuppressWarnings({"rawtypes","unchecked"})      Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];    table = newTab;    if (oldTab != null) {      for (int j = 0; j < oldCap; ++j) {        Node<K,V> e;        if ((e = oldTab[j]) != null) {          oldTab[j] = null;          if (e.next == null)            newTab[e.hash & (newCap - 1)] = e;          else if (e instanceof TreeNode)            ((TreeNode<K,V>)e).split(this, newTab, j, oldCap);          else { // preserve order            Node<K,V> loHead = null, loTail = null;            Node<K,V> hiHead = null, hiTail = null;            Node<K,V> next;            do {              next = e.next;              if ((e.hash & oldCap) == 0) {                if (loTail == null)                  loHead = e;                else                  loTail.next = e;                loTail = e;              }              else {                if (hiTail == null)                  hiHead = e;                else                  hiTail.next = e;                hiTail = e;              }            } while ((e = next) != null);            if (loTail != null) {              loTail.next = null;              newTab[j] = loHead;            }            if (hiTail != null) {              hiTail.next = null;              newTab[j + oldCap] = hiHead;            }          }        }      }    }    return newTab;  }