1.jdk1.8的结构
数组 + 链表 + 红黑树
2.链表
Node
hash
key
value
nextNode
3.数组
Node[] table
4.数组的长度是2的n次方
1.任何数和2的n次方-1做与运算都小于等于在2的n次方-1
刚好用来做hash计算数组的位子
2.任何数和2的n次方做与运算,只有两种结果0或者2的n次方
这个可以在resize的时候确定节点是高位和地位
5.put操作
如果hash出来的数组没有值,新建一个Node
if ((p = tab[i = (n - 1) & hash]) == null)
tab[i] = newNode(hash, key, value, null);
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)
//如果数组为空,先初始化
n = (tab = resize()).length;
if ((p = tab[i = (n - 1) & hash]) == null)
//如果hash出来的数组没有值,新建一个Node
tab[i] = newNode(hash, key, value, null);
else {
Node<K,V> e; K k;
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
//如果hash、key相等 值相等就替换
e = p;
else if (p instanceof TreeNode)
//如果是p是个树
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
else {
for (int binCount = 0; ; ++binCount) {
//死循环访问链表,直到最后一个节点(p.next)
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
//如果链表的长度大于 8-1,需要转成红黑树
treeifyBin(tab, hash);
break;
}
//如果链表中存在和key相等的元素跳出循环
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
if (e != null) { // existing mapping for key
//有key相等的
V oldValue = e.value;
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
++modCount;
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}