版权声明:取之网络,分享之网络. https://blog.csdn.net/qq_37751454/article/details/90175231
put操作:
public V put(K key, V value) {
return putVal(key, value, false);
}
/** Implementation for put and putIfAbsent */
final V putVal(K key, V value, boolean onlyIfAbsent) {
if (key == null || value == null) throw new NullPointerException();
int hash = spread(key.hashCode());
int binCount = 0;
for (Node<K,V>[] tab = table;;) {
Node<K,V> f; int n, i, fh;
if (tab == null || (n = tab.length) == 0)
// 1.初始化数组
tab = initTable();
// 2.取出key的hash值对应数组位置的节点(如果为null直接new一个节点,否则对该节点添加value)
else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
if (casTabAt(tab, i, null,
new Node<K,V>(hash, key, value, null)))
break; // no lock when adding to empty bin
}
// 3.数组正在扩容,该线程也帮助扩容
else if ((fh = f.hash) == MOVED)
tab = helpTransfer(tab, f);
// 4.对节点添加值
else {
V oldVal = null;
synchronized (f) {
if (tabAt(tab, i) == f) {
if (fh >= 0) {
binCount = 1;
// 4.1 链表结构
for (Node<K,V> e = f;; ++binCount) {
K ek;
// 4.1.1在对应位置替换value
if (e.hash == hash &&
((ek = e.key) == key ||
(ek != null && key.equals(ek)))) {
oldVal = e.val;
if (!onlyIfAbsent)
e.val = value;
break;
}
Node<K,V> pred = e;
// 4.1.2直接new node
if ((e = e.next) == null) {
pred.next = new Node<K,V>(hash, key,
value, null);
break;
}
}
}
// 4.2 树形结构
else if (f instanceof TreeBin) {
Node<K,V> p;
binCount = 2;
// 4.2.0 转化为树形结构进行put
if ((p = ((TreeBin<K,V>)f).putTreeVal(hash, key,
value)) != null) {
oldVal = p.val;
if (!onlyIfAbsent)
p.val = value;
}
}
}
}
if (binCount != 0) {
if (binCount >= TREEIFY_THRESHOLD)
treeifyBin(tab, i);
if (oldVal != null)
return oldVal;
break;
}
}
}
addCount(1L, binCount);
return null;
}