带中文注释的源码解析
putVal()
方法解析
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
boolean evict) {
Node<K,V>[] tab; Node<K,V> p; int n, i;
// 如果存储元素的table为空,则进行必要字段的初始化
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length; // 获取长度(16)
// 如果根据hash值获取的结点为空,则新建一个结点
if ((p = tab[i = (n - 1) & hash]) == null) // 此处 & 代替了 % (除法散列法进行散列)
tab[i] = newNode(hash, key, value, null);
// 这里的p结点是根据hash值算出来对应在数组中的元素
else {
Node<K,V> e; K k;
// 如果新插入的结点和table中p结点的hash值,key值相同的话
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
e = p;
// 如果是红黑树结点的话,进行红黑树插入
else if (p instanceof TreeNode)
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
else {
for (int binCount = 0; ; ++binCount) {
// 代表这个单链表只有一个头部结点,则直接新建一个结点即可
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);
// 链表长度大于8时,将链表转红黑树
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
treeifyBin(tab, hash);
break;
}
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
// 及时更新p
p = e;
}
}
// 如果存在这个映射就覆盖
if (e != null) { // existing mapping for key
V oldValue = e.value;
// 判断是否允许覆盖,并且value是否为空
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e); // 回调以允许LinkedHashMap后置操作
return oldValue;
}
}
++modCount; // 更改操作次数
if (++size > threshold) // 大于临界值
// 将数组大小设置为原来的2倍,并将原先的数组中的元素放到新数组中
// 因为有链表,红黑树之类,因此还要调整他们
resize();
// 回调以允许LinkedHashMap后置操作
afterNodeInsertion(evict);
return null;
}
resize()
解析:
//初始化或者扩容之后元素调整
final Node<K,V>[] resize() {
// 获取旧元素数组的各种信息
Node<K,V>[] oldTab = table;
// 长度
int oldCap = (oldTab == null) ? 0 : oldTab.length;
// 扩容的临界值
int oldThr = threshold;
// 定义新数组的长度及扩容的临界值
int newCap, newThr = 0;
if (oldCap > 0) { // 如果原table不为空
// 如果数组长度达到最大值,则修改临界值为Integer.MAX_VALUE
if (oldCap >= MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return oldTab;
}
// 下面就是扩容操作(2倍)
else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
oldCap >= DEFAULT_INITIAL_CAPACITY)
// threshold也变为二倍
newThr = oldThr << 1;
}
else if (oldThr > 0) // initial capacity was placed in threshold
newCap = oldThr;
else { // threshold为0,则使用默认值
newCap = DEFAULT_INITIAL_CAPACITY;
newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
}
if (newThr == 0) { // 如果临界值还为0,则设置临界值
float ft = (float)newCap * loadFactor;
newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
(int)ft : Integer.MAX_VALUE);
}
threshold = newThr; // 更新填充因子
@SuppressWarnings({"rawtypes","unchecked"})
Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
table = newTab;
if (oldTab != null) { // 调整数组大小之后,需要调整红黑树或者链表的指向
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) // 红黑树调整
((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
else { // preserve order
// 链表调整
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;
}
putTreeVal()
解析:
// 红黑树插入
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; // 找Root
for (TreeNode<K,V> p = root;;) {
int dir, ph; K pk;
if ((ph = p.hash) > h) // 红黑树中根据hash值、key值找结点
dir = -1;
else if (ph < h)
dir = 1;
else if ((pk = p.key) == k || (k != null && k.equals(pk))) // 找到则返回此节点
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) { // 没找到时
Node<K,V> xpn = xp.next;
TreeNode<K,V> x = map.newTreeNode(h, k, v, xpn); // 创建一个结点
if (dir <= 0) // 比较
xp.left = x;
else
xp.right = x;
xp.next = x; // 插入
x.parent = x.prev = xp;
if (xpn != null)
((TreeNode<K,V>)xpn).prev = x;
moveRootToFront(tab, balanceInsertion(root, x)); // 调整
return null;
}
}
}
treeifyBin()解析
// 链表转双向链表操作
final void treeifyBin(Node<K,V>[] tab, int hash) {
int n, index; Node<K,V> e;
// 如果元素总个数小于64,则继续进行扩容,结点指向调节
if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
resize();
// 先找到那个链表的头
else if ((e = tab[index = (n - 1) & hash]) != null) {
TreeNode<K,V> hd = null, tl = null;
do {
//创建红黑树根结点
TreeNode<K,V> p = replacementTreeNode(e, null);
if (tl == null)
hd = p;
else {
p.prev = tl;
tl.next = p;
}
tl = p;
} while ((e = e.next) != null);
if ((tab[index] = hd) != null)
// 此处才是真正的转为红黑树
hd.treeify(tab);
}
}
treeify()
解析
//将链表中每个值进行红黑树插入操作
final void treeify(Node<K,V>[] tab) {
TreeNode<K,V> root = null;
// TreeNode<K,V> x = this 相当于初始化了一个结点
for (TreeNode<K,V> x = this, next; x != null; x = next) {
next = (TreeNode<K,V>)x.next;
// 初始化Root
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 &&
// comparableClassFor(k) 返回 k 类型的比较器
(kc = comparableClassFor(k)) == null) ||
// compareComparables(kc, k, pk) 返回p,pk比较的结果
(dir = compareComparables(kc, k, pk)) == 0)
// tieBreakOrder(k, pk) 比较两个hash码
dir = tieBreakOrder(k, pk);
// 此处进行红黑树操作
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;
// 平衡调节
root = balanceInsertion(root, x);
break;
}
}
}
}
// 确保给定的根是根结点
moveRootToFront(tab, root);
}
balanceInsertion
()
解析
// 插入后的平衡操作
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;;) {
// 没有结点时
if ((xp = x.parent) == null) {
x.red = false;
return x;
}
// 只有两层的树
else if (!xp.red || (xpp = xp.parent) == null)
return root;
// 左子树插入
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);
}
}
}
}
// 右子树插入
else {
// 祖父结点不为空,并且颜色为红色时
if (xppl != null && xppl.red) {
xppl.red = false;
xp.red = false;
xpp.red = true;
x = xpp;
}
else {
// 左子树插入
if (x == xp.left) {
root = rotateRight(root, x = xp);
xpp = (xp = x.parent) == null ? null : xp.parent;
}
if (xp != null) {
// x 的父亲结点设置成黑色
xp.red = false;
if (xpp != null) {
// x的祖父结点设置成红色
xpp.red = true;
// 左旋
root = rotateLeft(root, xpp);
}
}
}
}
}
}
rotateLeft()
解析
配图:
// 红黑树的左旋操作
static <K,V> TreeNode<K,V> rotateLeft(TreeNode<K,V> root,
TreeNode<K,V> p) {
// r(right) 指的是调整点的右子树根结点
// pp(parentparent) 是p的祖父结点
// rl(rigthleft) 是p的叔父结点
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;
}