HashMap
2019-05-23 本文已影响0人
Pillar_Zhong
put
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
boolean evict) {
Node<K,V>[] tab; Node<K,V> p; int n, i;
// 如果是空，resize扩容
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length;
// 如果hash求余的位置空余，直接插入
if ((p = tab[i = (n - 1) & hash]) == null)
tab[i] = newNode(hash, key, value, null);
else {
Node<K,V> e; K k;
// 能找到对应hash+key匹配的位置
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
e = p;
// 如果是红黑树，直接插入
else if (p instanceof TreeNode)
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
else {
// 遍历链表
for (int binCount = 0; ; ++binCount) {
if ((e = p.next) == null) {
// 插入到链表末尾
p.next = newNode(hash, key, value, null);
// 如果超过阈值，链表转换成红黑树
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
treeifyBin(tab, hash);
break;
}
// 找到链表中对应的hash+key的位置结果
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
// 如果能之前已经存在，则这里用来更新已有的值
if (e != null) { // existing mapping for key
V oldValue = e.value;
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
// 设置该table已经更新
++modCount;
// 如果size已经超过阈值，立即扩容
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}
resize
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) {
// 如果旧的容量已经over，直接返回
if (oldCap >= MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return oldTab;
}
// 否则，在原来的基础上翻倍，且不能超过阈值
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);
}
// 根据新的容量，设置新的threshold
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) {
// 遍历原来的table
for (int j = 0; j < oldCap; ++j) {
Node<K,V> e;
if ((e = oldTab[j]) != null) {
oldTab[j] = null
// 如果该节点是单一元素，直接移动到新容器
if (e.next == null)
newTab[e.hash & (newCap - 1)] = e;
// 如果该节点是红黑树，移动到新容器中对应位置的红黑树中
else if (e instanceof TreeNode)
((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
// 否则就是链表
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;
// 举例：
// 假如 hash 值为 111001
// 扩容前 n=16(010000) n-1=15(01111) (n - 1)&hash=01111 & 111001=001001
// 扩容后 n=32(100000) n-1=31(11111) (n - 1)&hash=11111 & 111001=011001
// 最后的位置有变化 001001 -> 011001
// 假如 hash 值为 101001
// 扩容前 1111 & 101001 = 001001
// 扩容后 11111 & 101001 = 001001
// 最后的位置没变 001001
// hash & oldCap 的作用在于找到哪些扩容后，哪些hash对应的index不用变
// 101001 & 010000 = 0 但是 111001 & 010000 = 010000
if ((e.hash & oldCap) == 0) {
// 旧的部分从loHead开始
if (loTail == null)
loHead = e;
else
loTail.next = e;
loTail = e;
}
// 那么这里就是需要移动的部分，从hiHead开始
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;
}
// 新的部分的起始位置是原索引+原数组长度
if (hiTail != null) {
hiTail.next = null;
newTab[j + oldCap] = hiHead;
}
}
}
}
}
return newTab;
}
get
final Node<K,V> getNode(int hash, Object key) {
Node<K,V>[] tab; Node<K,V> first, e; int n; K k;
// 如果hash对应的位置不为空
if ((tab = table) != null && (n = tab.length) > 0 &&
(first = tab[(n - 1) & hash]) != null) {
// 如果hash+key相等，直接返回
if (first.hash == hash && // always check first node
((k = first.key) == key || (key != null && key.equals(k))))
return first;
if ((e = first.next) != null) {
// 如果是红黑树的部分，直接返回
if (first instanceof TreeNode)
return ((TreeNode<K,V>)first).getTreeNode(hash, key);
// 否则遍历链表，直到找到hash+key
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
return e;
} while ((e = e.next) != null);
}
}
return null;
}
remove
final Node<K,V> removeNode(int hash, Object key, Object value,
boolean matchValue, boolean movable) {
Node<K,V>[] tab; Node<K,V> p; int n, index;
// 或者hash+key对应的值
if ((tab = table) != null && (n = tab.length) > 0 &&
(p = tab[index = (n - 1) & hash]) != null) {
Node<K,V> node = null, e; K k; V v;
// 直接在主链中找到
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
node = p;
else if ((e = p.next) != null) {
// 去红黑树找
if (p instanceof TreeNode)
node = ((TreeNode<K,V>)p).getTreeNode(hash, key);
// 去链表找
else {
do {
if (e.hash == hash &&
((k = e.key) == key ||
(key != null && key.equals(k)))) {
node = e;
break;
}
p = e;
} while ((e = e.next) != null);
}
}
if (node != null && (!matchValue || (v = node.value) == value ||
(value != null && value.equals(v)))) {
// 如果是红黑树，去那边删除
if (node instanceof TreeNode)
((TreeNode<K,V>)node).removeTreeNode(this, tab, movable);
else if (node == p)
tab[index] = node.next;
else
// 跳过该节点，也就是删除
p.next = node.next;
++modCount;
--size;
afterNodeRemoval(node);
return node;
}
}
return null;
}
