e, p;
int n, eh;
K ek;
int h = spread(key.hashCode());
if ((tab = table) != null && (n = tab.length) > 0 &&
(e = tabAt(tab, (n - 1) & h)) != null) {
if ((eh = e.hash) == h) {
if ((ek = e.key) == key || (ek != null && key.equals(ek)))
return e.val;
}
else if (eh < 0)
return (p = e.find(h, key)) != null ? p.val : null;
while ((e = e.next) != null) {
if (e.hash == h &&
((ek = e.key) == key || (ek != null && key.equals(ek))))
return e.val;
}
}
return null;
}
```
public V put(K key, V value) {
return putVal(key, value, false);
}
/**
* 在 putVal 方法中使用了两种同步机制：
* 1. CAS：使用 CAS 在 Node 数组中增加节点
* 2. 分段锁：每一个哈希桶中的列表，都使用头节点作为锁对象
*/
final V putVal(K key, V value, boolean onlyIfAbsent) {
...
for (Node<K,V>[] tab = table;;) {
...
else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
if (casTabAt(tab, i, null, new Node<K,V>(hash, key, value)))
break; // no lock when adding to empty bin
}
...
else {
V oldVal = null;
synchronized (f) {
...
}
...
}
}
addCount(1L, binCount);
return null;
}
```java
public int size() {
long n = sumCount();
return ((n < 0L) ? 0 :
(n > (long)Integer.MAX_VALUE) ? Integer.MAX_VALUE :
(int)n);
}
final long sumCount() {
CounterCell[] cs = counterCells;
long sum = baseCount;
if (cs != null) {
for (CounterCell c : cs)
if (c != null)
sum += c.value;
}
return sum;
}
/**
* A padded cell for distributing counts. Adapted from LongAdder
* and Striped64. See their internal docs for explanation.
*/
@jdk.internal.vm.annotation.Contended static final class CounterCell {
volatile long value;
CounterCell(long x) { value = x; }
}
```