Hash Map
[TOC]
HashMap
特点
基于Map接口；
允许Key和Value都允许为null；
非同步；
不保证顺序和插入时相同；
不保证顺序时不变。
原理
Put的流程
st=>start: start
c1=>condition: table是否未初始化
c2=>condition: table[i]是否为null
c3=>condition: table[i]的hash、Key是否与当前加入节点的hash、key一样
c4=>condition: tablke[i]是否TreeNode类型
c5=>condition: 当前节点是否为null
c6=>condition: 当前链表的节点是否超过TREEIFY_THRESHOLD
c7=>condition: 当前节点的hash、key是否一样
c8=>condition: e是否为Null
o1=>operation: 进行resize
o2=>operation: 根据Hash结果找到table[i]
o3=>operation: newNode放入table[i]
o4=>operation: 将当前值复制给e
o5=>operation: 使用TreeNode方式put节点
o6=>operation: 使用链表方式put节点
o7=>operation: 取链表的第一个节点
o8=>operation: newNode放入p.next
o9=>operation: 对链表进行treeifyBin（即进行链表转树）
o10=>operation: 已找到当前节点等于目标节点，break
o11=>operation: 取链表下一节点
o12=>operation: 替换e的值并返回e的旧值
end=>end: end
st->c1
c1(yes)->o1->o2
c1(no)->o2
o2->c2
c2(yes)->o3
c2(no)->c3
c3(yes)->o4
c3(no)->c4
c4(yes)->o5
c4(no)->o6
o6->o7->c5
c5(yes)->o8->c6(yes)->o9
c5(no)->c7
c7(yes)->o10
c7(no)->o11->c5
o4->c8
o5->c8
o10->c8
o9->c8
c8(yes)->o12
c5->endHash如何计算
static final int hash(Object key) {
int h;
// key为null，hash为0，否则，取Object的hashCode，然后取hashCode的高位，与自己异或
return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}1、为什么要右移?
尽可能的防止Hash碰撞，本身具有高随机性的HashCode，在高低位异或一下，一定程度上能增强随机性。
2、为什么要用异或？ A、效率高
B、对比效率高的操作还有位与( & )、位或( | )。
假设是位与，则0-0=0，0-1=0，1-0=0，1-1=1，可知75%的概率位0，25%概率位1，概率不均。
假设是位或，则0-0=0，0-1=1，1-0=1，1-1=1，可知75%的概率位1，25%概率位0，概率不均。
假设是异或，则0-0=1，0-1=0，1-0=0，1-1=1，可知50%的概率位1，50%概率位0，概率均等。
长度为什么是2n
/**
* 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;为了能让 HashMap 存取高效，尽量较少碰撞，也就是要尽量把数据分配均匀。
看了上面一句话，大家可能并不能理解具体原因，下面就带着大伙根据源码解释下上面的这句话。首先，HashMap内部维护了一个Node数组，每次根据key查询value，都需要计算key的hash，然后在根据hash去计算Node数组的下标获取对应的Node，那么HashMap现在是如何计算下标的呢？
计算高效
Hash值的范围值-2147483648到2147483647，前后加起来大概40亿的映射空间，只要哈希函数映射得比较均匀松散，一般应用是很难出现碰撞的。但问题是一个40亿长度的数组，内存是放不下的。所以这个散列值是不能直接拿来用的。那怎么设计呢？很多人可能想到取余（hash % length）这个方法，固然可以，但是不高效呀。所以通过翻阅HashMap源码，我们得知了HashMap选择了(n - 1) & hash这个计算公式（PS：见下方getNode方法），n代表数组长度。
public V get(Object key) {
Node<K,V> e;
return (e = getNode(hash(key), key)) == null ? null : e.value;
}
final Node<K,V> getNode(int hash, Object key) {
Node<K,V>[] tab; Node<K,V> first, e; int n; K k;
if ((tab = table) != null && (n = tab.length) > 0 &&
// 此处计算下标的公式为(n - 1) & hash
(first = tab[(n - 1) & hash]) != null) {
// 1、检查Hash是否相等 2、检查Object是否相等
if (first.hash == hash && // always check first node
((k = first.key) == key || (key != null && key.equals(k))))
// 如果相等，直接返回
return first;
// 检查节点的next是否存在
if ((e = first.next) != null) {
// 检查节点是否为树
if (first instanceof TreeNode)
return ((TreeNode<K,V>)first).getTreeNode(hash, key);
do {
// 如果是链表，则按顺序遍历，直到找到目标节点
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
return e;
} while ((e = e.next) != null);
}
}
return null;
}等等，大伙此时肯定想问，啊，这个公式虽然简单、优雅，能称得上计算高效，但是就能说明HashMap的长度是2n了吗？是的，但是为什么呢，咱们继续往下看。
降低碰撞
大伙都知道，HashMap高不高效，其中一个最重要的因素便是Hash算法要好。作为HashMap的设计者，肯定也知道这一点，所以在设计HashMap的时候，将这一点完全托付给了Hash算法，即相信Hash算法能够设计好。而HashMap计算下标，则以不影响Hash算法结果的目的而设计。那么保证HashMap的长度是2n，就能保证不影响到Hash算法结果，至于为什么，咱们接着向下看。
对于HashMap计算下标的公式：(n - 1) & hash，我们假设一下：
n是奇数，则n-1为偶数。比如n=5，n-1转为二进制则为100。
n是偶数，且不是2的幂次方，则n-1为奇数。比如n=6，n-1转为二进制则为101。
n是偶数，且是2的幂次方，则n-1为奇数。比如n=4，n-1转为二进制则为11，假设n=8呢，n-1转为二进制则为111。
不知道大伙有没有发现规律，只要是2n-1，转为二进制，所有位置上均为1，1与任何数的结果都是任何数。哇，巧妙不，没有影响hash值，而且还按照预期要求，保留了自己需要的低位数据。
到此为止，基本上讲清楚了为啥HashMap的长度是2n了。
源码
putVal
public V put(K key, V value) {
return putVal(hash(key), key, value, false, true);
}
/**
* Implements Map.put and related methods.
*
* @param hash hash for key
* @param key the key
* @param value the value to put
* @param onlyIfAbsent if true, don't change existing value
* @param evict if false, the table is in creation mode.
* @return previous value, or null if none
*/
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
boolean evict) {
Node<K,V>[] tab; Node<K,V> p; int n, i;
if ((tab = table) == null || (n = tab.length) == 0)
// 初始化
n = (tab = resize()).length;
// Node数组对应的位置是否为null
if ((p = tab[i = (n - 1) & hash]) == null)
// 无Hash冲突的情况
tab[i] = newNode(hash, key, value, null);
else {
// 处理Hash冲突的情况
Node<K,V> e; K k;
// 判断对应下标的Node，与新Node的Hash、Key地址、Key的eqauls是否相同
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
// 如果相同，则表示新加入的Node已经在HashMap中了，直接返回老Node的引用即可
e = p;
// 判断是否是树
else if (p instanceof TreeNode)
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
else {
// 此时一定是链表，顺序遍历，直到遍历到队尾
for (int binCount = 0; ; ++binCount) {
// 判断是否到了链表队尾
if ((e = p.next) == null) {
// 直接在队尾插入新的Node
p.next = newNode(hash, key, value, null);
// 判断当前是否满足转树的条件，TREEIFY_THRESHOLD = 8，binCount表示遍历次数，即链表长度
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
// 转树
treeifyBin(tab, hash);
break;
}
// 判断当前遍历到的节点，与新Node的Hash、Key地址、Key的eqauls是否相同
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
// 如果相同，则表示新加入的Node已经在HashMap的链表中了，直接返回老Node的引用即可
break;
// 继续下一节点
p = e;
}
}
if (e != null) { // existing mapping for key
V oldValue = e.value;
// 是否要替换老节点Value
if (!onlyIfAbsent || oldValue == null)
e.value = value;
// 为LinkedHashMap扩展使用，表示新Node的访问
afterNodeAccess(e);
return oldValue;
}
}
++modCount;
// 当Size大于阀值的时候，进行resize
if (++size > threshold)
resize();
// 为LinkedHashMap扩展使用，表示新Node的插入
afterNodeInsertion(evict);
return null;
}treeifyBin
/**
* 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.
*
* 可对其进行树转化的最小表容量。
*（否则，如果 bin 中有太多节点，则调整表的大小。）
* 应至少为 4 * TREEIFY_THRESHOLD 以避免调整大小和树化阈值之间的冲突。
*/
static final int MIN_TREEIFY_CAPACITY = 64;
/**
* Replaces all linked nodes in bin at index for given hash unless
* table is too small, in which case resizes instead.
*/
final void treeifyBin(Node<K,V>[] tab, int hash) {
int n, index; Node<K,V> e;
// 判断tab是否未初始化，或者tab的长度小于树化的阀值
if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
// 调整大小
resize();
// 判断下Hash对应下标的数组节点是否存在
else if ((e = tab[index = (n - 1) & hash]) != null) {
TreeNode<K,V> hd = null, tl = null;
do {
// Node节点转树节点
TreeNode<K,V> p = replacementTreeNode(e, null);
if (tl == null)
// 根节点记录引用
hd = p;
else {
// 当前节点的prev指向前置节点
p.prev = tl;
// 前置节点的next指向当前节点
tl.next = p;
}
// tl主要记录上一节点
tl = p;
// 继续遍历链表的下一个节点
} while ((e = e.next) != null);
// 判断根节点不为空，且将根节点放入数组中
if ((tab[index] = hd) != null)
// 树化
hd.treeify(tab);
}
}TreeNode
红黑树的实现都在这里了。
static final class TreeNode<K,V> extends LinkedHashMap.Entry<K,V> {
TreeNode<K,V> parent; // red-black tree links
TreeNode<K,V> left;
TreeNode<K,V> right;
TreeNode<K,V> prev; // needed to unlink next upon deletion
boolean red;
TreeNode(int hash, K key, V val, Node<K,V> next) {
super(hash, key, val, next);
}
/**
* Returns root of tree containing this node.
*/
final TreeNode<K,V> root() {
for (TreeNode<K,V> r = this, p;;) {
if ((p = r.parent) == null)
return r;
r = p;
}
}
/**
* Ensures that the given root is the first node of its bin.
*/
static <K,V> void moveRootToFront(Node<K,V>[] tab, TreeNode<K,V> root) {
int n;
if (root != null && tab != null && (n = tab.length) > 0) {
int index = (n - 1) & root.hash;
TreeNode<K,V> first = (TreeNode<K,V>)tab[index];
if (root != first) {
Node<K,V> rn;
tab[index] = root;
TreeNode<K,V> rp = root.prev;
if ((rn = root.next) != null)
((TreeNode<K,V>)rn).prev = rp;
if (rp != null)
rp.next = rn;
if (first != null)
first.prev = root;
root.next = first;
root.prev = null;
}
assert checkInvariants(root);
}
}
/**
* Finds the node starting at root p with the given hash and key.
* The kc argument caches comparableClassFor(key) upon first use
* comparing keys.
*/
final TreeNode<K,V> find(int h, Object k, Class<?> kc) {
TreeNode<K,V> p = this;
do {
int ph, dir; K pk;
TreeNode<K,V> pl = p.left, pr = p.right, q;
if ((ph = p.hash) > h)
p = pl;
else if (ph < h)
p = pr;
else if ((pk = p.key) == k || (k != null && k.equals(pk)))
return p;
else if (pl == null)
p = pr;
else if (pr == null)
p = pl;
else if ((kc != null ||
(kc = comparableClassFor(k)) != null) &&
(dir = compareComparables(kc, k, pk)) != 0)
p = (dir < 0) ? pl : pr;
else if ((q = pr.find(h, k, kc)) != null)
return q;
else
p = pl;
} while (p != null);
return null;
}
/**
* Calls find for root node.
*/
final TreeNode<K,V> getTreeNode(int h, Object k) {
return ((parent != null) ? root() : this).find(h, k, null);
}
/**
* Tie-breaking utility for ordering insertions when equal
* hashCodes and non-comparable. We don't require a total
* order, just a consistent insertion rule to maintain
* equivalence across rebalancings. Tie-breaking further than
* necessary simplifies testing a bit.
*/
static int tieBreakOrder(Object a, Object b) {
int d;
if (a == null || b == null ||
(d = a.getClass().getName().
compareTo(b.getClass().getName())) == 0)
d = (System.identityHashCode(a) <= System.identityHashCode(b) ?
-1 : 1);
return d;
}
/**
* Forms tree of the nodes linked from this node.
*/
final void treeify(Node<K,V>[] tab) {
TreeNode<K,V> root = null;
for (TreeNode<K,V> x = this, next; x != null; x = next) {
next = (TreeNode<K,V>)x.next;
x.left = x.right = null;
if (root == null) {
x.parent = null;
x.red = false;
root = x;
}
else {
K k = x.key;
int h = x.hash;
Class<?> kc = null;
for (TreeNode<K,V> p = root;;) {
int dir, ph;
K pk = p.key;
if ((ph = p.hash) > h)
dir = -1;
else if (ph < h)
dir = 1;
else if ((kc == null &&
(kc = comparableClassFor(k)) == null) ||
(dir = compareComparables(kc, k, pk)) == 0)
dir = tieBreakOrder(k, pk);
TreeNode<K,V> xp = p;
if ((p = (dir <= 0) ? p.left : p.right) == null) {
x.parent = xp;
if (dir <= 0)
xp.left = x;
else
xp.right = x;
root = balanceInsertion(root, x);
break;
}
}
}
}
moveRootToFront(tab, root);
}
/**
* Returns a list of non-TreeNodes replacing those linked from
* this node.
*/
final Node<K,V> untreeify(HashMap<K,V> map) {
Node<K,V> hd = null, tl = null;
for (Node<K,V> q = this; q != null; q = q.next) {
Node<K,V> p = map.replacementNode(q, null);
if (tl == null)
hd = p;
else
tl.next = p;
tl = p;
}
return hd;
}
/**
* Tree version of putVal.
*/
final TreeNode<K,V> putTreeVal(HashMap<K,V> map, Node<K,V>[] tab,
int h, K k, V v) {
Class<?> kc = null;
boolean searched = false;
TreeNode<K,V> root = (parent != null) ? root() : this;
for (TreeNode<K,V> p = root;;) {
int dir, ph; K pk;
if ((ph = p.hash) > h)
dir = -1;
else if (ph < h)
dir = 1;
else if ((pk = p.key) == k || (k != null && k.equals(pk)))
return p;
else if ((kc == null &&
(kc = comparableClassFor(k)) == null) ||
(dir = compareComparables(kc, k, pk)) == 0) {
if (!searched) {
TreeNode<K,V> q, ch;
searched = true;
if (((ch = p.left) != null &&
(q = ch.find(h, k, kc)) != null) ||
((ch = p.right) != null &&
(q = ch.find(h, k, kc)) != null))
return q;
}
dir = tieBreakOrder(k, pk);
}
TreeNode<K,V> xp = p;
if ((p = (dir <= 0) ? p.left : p.right) == null) {
Node<K,V> xpn = xp.next;
TreeNode<K,V> x = map.newTreeNode(h, k, v, xpn);
if (dir <= 0)
xp.left = x;
else
xp.right = x;
xp.next = x;
x.parent = x.prev = xp;
if (xpn != null)
((TreeNode<K,V>)xpn).prev = x;
moveRootToFront(tab, balanceInsertion(root, x));
return null;
}
}
}
/**
* Removes the given node, that must be present before this call.
* This is messier than typical red-black deletion code because we
* cannot swap the contents of an interior node with a leaf
* successor that is pinned by "next" pointers that are accessible
* independently during traversal. So instead we swap the tree
* linkages. If the current tree appears to have too few nodes,
* the bin is converted back to a plain bin. (The test triggers
* somewhere between 2 and 6 nodes, depending on tree structure).
*/
final void removeTreeNode(HashMap<K,V> map, Node<K,V>[] tab,
boolean movable) {
int n;
if (tab == null || (n = tab.length) == 0)
return;
int index = (n - 1) & hash;
TreeNode<K,V> first = (TreeNode<K,V>)tab[index], root = first, rl;
TreeNode<K,V> succ = (TreeNode<K,V>)next, pred = prev;
if (pred == null)
tab[index] = first = succ;
else
pred.next = succ;
if (succ != null)
succ.prev = pred;
if (first == null)
return;
if (root.parent != null)
root = root.root();
if (root == null
|| (movable
&& (root.right == null
|| (rl = root.left) == null
|| rl.left == null))) {
tab[index] = first.untreeify(map); // too small
return;
}
TreeNode<K,V> p = this, pl = left, pr = right, replacement;
if (pl != null && pr != null) {
TreeNode<K,V> s = pr, sl;
while ((sl = s.left) != null) // find successor
s = sl;
boolean c = s.red; s.red = p.red; p.red = c; // swap colors
TreeNode<K,V> sr = s.right;
TreeNode<K,V> pp = p.parent;
if (s == pr) { // p was s's direct parent
p.parent = s;
s.right = p;
}
else {
TreeNode<K,V> sp = s.parent;
if ((p.parent = sp) != null) {
if (s == sp.left)
sp.left = p;
else
sp.right = p;
}
if ((s.right = pr) != null)
pr.parent = s;
}
p.left = null;
if ((p.right = sr) != null)
sr.parent = p;
if ((s.left = pl) != null)
pl.parent = s;
if ((s.parent = pp) == null)
root = s;
else if (p == pp.left)
pp.left = s;
else
pp.right = s;
if (sr != null)
replacement = sr;
else
replacement = p;
}
else if (pl != null)
replacement = pl;
else if (pr != null)
replacement = pr;
else
replacement = p;
if (replacement != p) {
TreeNode<K,V> pp = replacement.parent = p.parent;
if (pp == null)
(root = replacement).red = false;
else if (p == pp.left)
pp.left = replacement;
else
pp.right = replacement;
p.left = p.right = p.parent = null;
}
TreeNode<K,V> r = p.red ? root : balanceDeletion(root, replacement);
if (replacement == p) { // detach
TreeNode<K,V> pp = p.parent;
p.parent = null;
if (pp != null) {
if (p == pp.left)
pp.left = null;
else if (p == pp.right)
pp.right = null;
}
}
if (movable)
moveRootToFront(tab, r);
}
/**
* Splits nodes in a tree bin into lower and upper tree bins,
* or untreeifies if now too small. Called only from resize;
* see above discussion about split bits and indices.
*
* @param map the map
* @param tab the table for recording bin heads
* @param index the index of the table being split
* @param bit the bit of hash to split on
*/
final void split(HashMap<K,V> map, Node<K,V>[] tab, int index, int bit) {
TreeNode<K,V> b = this;
// Relink into lo and hi lists, preserving order
TreeNode<K,V> loHead = null, loTail = null;
TreeNode<K,V> hiHead = null, hiTail = null;
int lc = 0, hc = 0;
for (TreeNode<K,V> e = b, next; e != null; e = next) {
next = (TreeNode<K,V>)e.next;
e.next = null;
if ((e.hash & bit) == 0) {
if ((e.prev = loTail) == null)
loHead = e;
else
loTail.next = e;
loTail = e;
++lc;
}
else {
if ((e.prev = hiTail) == null)
hiHead = e;
else
hiTail.next = e;
hiTail = e;
++hc;
}
}
if (loHead != null) {
if (lc <= UNTREEIFY_THRESHOLD)
tab[index] = loHead.untreeify(map);
else {
tab[index] = loHead;
if (hiHead != null) // (else is already treeified)
loHead.treeify(tab);
}
}
if (hiHead != null) {
if (hc <= UNTREEIFY_THRESHOLD)
tab[index + bit] = hiHead.untreeify(map);
else {
tab[index + bit] = hiHead;
if (loHead != null)
hiHead.treeify(tab);
}
}
}
/* ------------------------------------------------------------ */
// Red-black tree methods, all adapted from CLR
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;
}
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;
}
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)
return root;
if (xp == (xppl = xpp.left)) {
if ((xppr = xpp.right) != null && xppr.red) {
xppr.red = false;
xp.red = false;
xpp.red = true;
x = xpp;
}
else {
if (x == xp.right) {
root = rotateLeft(root, x = xp);
xpp = (xp = x.parent) == null ? null : xp.parent;
}
if (xp != null) {
xp.red = false;
if (xpp != null) {
xpp.red = true;
root = rotateRight(root, xpp);
}
}
}
}
else {
if (xppl != null && xppl.red) {
xppl.red = false;
xp.red = false;
xpp.red = true;
x = xpp;
}
else {
if (x == xp.left) {
root = rotateRight(root, x = xp);
xpp = (xp = x.parent) == null ? null : xp.parent;
}
if (xp != null) {
xp.red = false;
if (xpp != null) {
xpp.red = true;
root = rotateLeft(root, xpp);
}
}
}
}
}
}
static <K,V> TreeNode<K,V> balanceDeletion(TreeNode<K,V> root,
TreeNode<K,V> x) {
for (TreeNode<K,V> xp, xpl, xpr;;) {
if (x == null || x == root)
return root;
else if ((xp = x.parent) == null) {
x.red = false;
return x;
}
else if (x.red) {
x.red = false;
return root;
}
else if ((xpl = xp.left) == x) {
if ((xpr = xp.right) != null && xpr.red) {
xpr.red = false;
xp.red = true;
root = rotateLeft(root, xp);
xpr = (xp = x.parent) == null ? null : xp.right;
}
if (xpr == null)
x = xp;
else {
TreeNode<K,V> sl = xpr.left, sr = xpr.right;
if ((sr == null || !sr.red) &&
(sl == null || !sl.red)) {
xpr.red = true;
x = xp;
}
else {
if (sr == null || !sr.red) {
if (sl != null)
sl.red = false;
xpr.red = true;
root = rotateRight(root, xpr);
xpr = (xp = x.parent) == null ?
null : xp.right;
}
if (xpr != null) {
xpr.red = (xp == null) ? false : xp.red;
if ((sr = xpr.right) != null)
sr.red = false;
}
if (xp != null) {
xp.red = false;
root = rotateLeft(root, xp);
}
x = root;
}
}
}
else { // symmetric
if (xpl != null && xpl.red) {
xpl.red = false;
xp.red = true;
root = rotateRight(root, xp);
xpl = (xp = x.parent) == null ? null : xp.left;
}
if (xpl == null)
x = xp;
else {
TreeNode<K,V> sl = xpl.left, sr = xpl.right;
if ((sl == null || !sl.red) &&
(sr == null || !sr.red)) {
xpl.red = true;
x = xp;
}
else {
if (sl == null || !sl.red) {
if (sr != null)
sr.red = false;
xpl.red = true;
root = rotateLeft(root, xpl);
xpl = (xp = x.parent) == null ?
null : xp.left;
}
if (xpl != null) {
xpl.red = (xp == null) ? false : xp.red;
if ((sl = xpl.left) != null)
sl.red = false;
}
if (xp != null) {
xp.red = false;
root = rotateRight(root, xp);
}
x = root;
}
}
}
}
}
/**
* Recursive invariant check
*/
static <K,V> boolean checkInvariants(TreeNode<K,V> t) {
TreeNode<K,V> tp = t.parent, tl = t.left, tr = t.right,
tb = t.prev, tn = (TreeNode<K,V>)t.next;
if (tb != null && tb.next != t)
return false;
if (tn != null && tn.prev != t)
return false;
if (tp != null && t != tp.left && t != tp.right)
return false;
if (tl != null && (tl.parent != t || tl.hash > t.hash))
return false;
if (tr != null && (tr.parent != t || tr.hash < t.hash))
return false;
if (t.red && tl != null && tl.red && tr != null && tr.red)
return false;
if (tl != null && !checkInvariants(tl))
return false;
if (tr != null && !checkInvariants(tr))
return false;
return true;
}
}
resize
/**
* 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.
*
* 即2<sup>30</sup>
*/
static final int MAXIMUM_CAPACITY = 1 << 30;
// 扩容
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) {
// 判断老容量是否大于MAXIMUM_CAPACITY
if (oldCap >= MAXIMUM_CAPACITY) {
// 阀值赋值为Integer.MAX_VALUE
threshold = Integer.MAX_VALUE;
// 后续不再扩容了
return oldTab;
}
// 否则，新容量扩大为2倍，在判断新容量是否小于MAXIMUM_CAPACITY且老容量大于等于默认容量
else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
oldCap >= DEFAULT_INITIAL_CAPACITY)
// 新阀值扩大为2倍
newThr = oldThr << 1; // double threshold
}
else if (oldThr > 0) // initial capacity was placed in threshold
// 老容量小于等于0，且老阀值大于0，则新容量等于老阀值
newCap = oldThr;
else { // zero initial threshold signifies using defaults
// 老容量小于等于0，且老阀值小于等于0，直接进行初始化，新容量为默认容量，新阀值为负载因子*默认容量
newCap = DEFAULT_INITIAL_CAPACITY;
newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
}
// 新阀值如果为0
if (newThr == 0) {
// 新阀值等于新容量*负载因子
float ft = (float)newCap * loadFactor;
// 新容量、新阀值小于最大容量，则使用新阀值，否则使用Integer.MAX_VALUE
newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
(int)ft : Integer.MAX_VALUE);
}
threshold = newThr;
@SuppressWarnings({"rawtypes","unchecked"})
// 创建新的数组
Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
table = newTab;
if (oldTab != null) {
// 老数组复制到新的数组
for (int j = 0; j < oldCap; ++j) {
Node<K,V> e;
if ((e = oldTab[j]) != null) {
// 老数组释放引用
oldTab[j] = null;
if (e.next == null)
// 普通节点，即非链表、非树，直接赋值
newTab[e.hash & (newCap - 1)] = e;
else if (e instanceof TreeNode)
// 树处理
((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
else { // preserve order
// 链表处理
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;
}Last updated
