执行添加操作
执行put,该方法会执行hash(key)方法得到对应的hash值,不等价于HashCode
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
boolean evict) {
HashMap.Node<K,V>[] tab; HashMap.Node<K,V> p; int n, i;
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length;
if ((p = tab[i = (n - 1) & hash]) == null)
tab[i] = newNode(hash, key, value, null);
else {
HashMap.Node<K,V> e; K k;
//如果当前索引位置对应的第一个元素和准备添加的key的hash值一样
//并且满足下面两个条件之一:
//(1)准备加入的key和p指向的node的节点的key是同一个对象
//(2)p指向的node节点的key的equals()和准备加入的key比较后相同
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
e = p;
//再判断p是不是一颗红黑树
//如果是一颗红黑树,调用putTreeVal进行添加
else if (p instanceof HashMap.TreeNode)
e = ((HashMap.TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
//如果table对应的索引位置已经是一个链表,使用for循环比较
//(1)依次和该链表的每个元素比较后都不相同,加入该链表的最后
//在把元素添加到链表后,立即判断,该链表是否已经达到8个节点,就调用treeifyBin()对当前这个链表进行树化(转成红黑树)
//注意:在转成红黑树时,要进行判断,判断条件如下:if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY) resize();
//如果上面条件成立,先table扩容
//只有上面条件不成立时,转成红黑树
//(2)依次和该链表的每一个元素比较过程中,如果有相同就break
else {
for (int binCount = 0; ; ++binCount) {
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);
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;
p = e;
}
}
if (e != null) {
// existing mapping for key
V oldValue = e.value;
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
++modCount;
//size 就是我们每加入一个节点Node(k,v,next) Size++
if (++size > threshold)
resize(); //扩容
afterNodeInsertion(evict);
return null;
}
final void treeifyBin(Node<K,V>[] tab, int hash) {
int n, index; Node<K,V> e;
if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
resize();
else if ((e = tab[index = (n - 1) & hash]) != null) {
TreeNode<K,V> hd = null, tl = null;
do {
//替换成红黑树replacementTreeNode()
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)
hd.treeify(tab);
}