Java数据结构-HashMap详解

2019-11-26 09:11:21

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Java数据结构-HashMap

1. HashMap数据结构

没有哈希冲突时，为数组，支持动态扩容

哈希冲突时，分为两种情况：

1.当冲突长度小于8或数组长度小于64（MIN_TREEIFY_CAPACITY默认值为64）时，为数组+链表（Node）

2.当冲突长度大于8时，为数组+红黑树/链表(TreeNode)。

红黑树用于快速查找，链表用于遍历。

2. 红黑树

HashMap中的TreeNode是红黑树的实现。

TreeNode几个方法

1. 左旋转

static <K,V> TreeNode<K,V> rotateLeft(TreeNode<K,V> root,                       TreeNode<K,V> p) {      TreeNode<K,V> r, pp, rl;      if (p != null && (r = p.right) != null) {        if ((rl = p.right = r.left) != null)          rl.parent = p;        if ((pp = r.parent = p.parent) == null)          (root = r).red = false;        else if (pp.left == p)          pp.left = r;        else          pp.right = r;        r.left = p;        p.parent = r;      }      return root;    }

实现效果如图

2. 右旋转

static <K,V> TreeNode<K,V> rotateRight(TreeNode<K,V> root,                        TreeNode<K,V> p) {      TreeNode<K,V> l, pp, lr;      if (p != null && (l = p.left) != null) {        if ((lr = p.left = l.right) != null)          lr.parent = p;        if ((pp = l.parent = p.parent) == null)          (root = l).red = false;        else if (pp.right == p)          pp.right = l;        else          pp.left = l;        l.right = p;        p.parent = l;      }      return root;    }

实现效果如图

3. 插入

static <K,V> TreeNode<K,V> balanceInsertion(TreeNode<K,V> root,                          TreeNode<K,V> x) {      x.red = true;      for (TreeNode<K,V> xp, xpp, xppl, xppr;;) {        if ((xp = x.parent) == null) {          x.red = false;          return x;        }        else if (!xp.red || (xpp = xp.parent) == null) //①          return root;        if (xp == (xppl = xpp.left)) {          if ((xppr = xpp.right) != null && xppr.red) { //②            xppr.red = false;            xp.red = false;            xpp.red = true;            x = xpp;          }          else {            if (x == xp.right) { //③              root = rotateLeft(root, x = xp);              xpp = (xp = x.parent) == null ? null : xp.parent;            }            if (xp != null) { //④              xp.red = false;              if (xpp != null) {                xpp.red = true;                root = rotateRight(root, xpp);              }            }          }        }        else {          if (xppl != null && xppl.red) { //②            xppl.red = false;            xp.red = false;            xpp.red = true;            x = xpp;          }          else {            if (x == xp.left) {    //⑤              root = rotateRight(root, x = xp);              xpp = (xp = x.parent) == null ? null : xp.parent;            }            if (xp != null) {  //⑥              xp.red = false;              if (xpp != null) {                xpp.red = true;                root = rotateLeft(root, xpp);              }            }          }        }      }    }

实现效果如下：