HashMap相关

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)
// 初始的判断
// resize() 初始数组 扩容 初始的时候 获取了一个容量为16的数组
n = (tab = resize()).length; // n 数组长度
// 确定插入的key在数组中的下标 15 11111
// 100001000111000
// 1111
// 1000 = 8
if ((p = tab[i = (n - 1) & hash]) == null)
// 通过hash值找到的数组的下标 里面没有内容就直接赋值
tab[i] = newNode(hash, key, value, null);
else {
Node<K,V> e; K k;
if (p.hash == hash // hash值相同&&
// key也相同
((k = p.key) == key || (key != null && key.equals(k))))
// 插入的值的key 和 数组当前位置的 key是同一个 那么直接修改里面内容
e = p;
else if (p instanceof TreeNode)
// 表示 数组中存放的节点是一个 红黑树节点
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
else {
// 表示节点就是普通的链表
for (int binCount = 0; ; ++binCount) {
if ((e = p.next) == null) {
// 到了链表的尾部
p.next = newNode(hash, key, value, null);
// 将新的节点添加到了链表的尾部
// 判断是否满足 链表转红黑树的条件
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
// 转红黑树
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;
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}

final void treeifyBin(Node<K,V>[] tab, int hash) {
int n, index; Node<K,V> e;
// tab为空 或者 数组的长度小于64
if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
resize(); // 扩容
else if ((e = tab[index = (n - 1) & hash]) != null) {
// 链表转红黑树的逻辑
TreeNode<K,V> hd = null, tl = null;
do {
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);
}
}

    final Node<K,V>[] resize() {
        // [1,2,3,4,5,6,7,8,9,10,11,,,,]
        Node<K,V>[] oldTab = table;
        // 16
        int oldCap = (oldTab == null) ? 0 : oldTab.length;
        // 12
        int oldThr = threshold;
        int newCap, newThr = 0;
        if (oldCap > 0) {
            if (oldCap >= MAXIMUM_CAPACITY) {
                threshold = Integer.MAX_VALUE;
                return oldTab;
            }
            // 新的容量是 原来容量的两倍
            else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
                     oldCap >= DEFAULT_INITIAL_CAPACITY)
                // 扩容的临界值  原来的两倍 24
                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);
        }
        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"})
        // 创建的数组的长度是32
        Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
        table = newTab;
        if (oldTab != null) { // 初始的时候是不需要复制的
            for (int j = 0; j < oldCap; ++j) {
                Node<K,V> e;
                if ((e = oldTab[j]) != null) {
                    oldTab[j] = null;
                    if (e.next == null)
                        // 数组中的元素就一个 找到元素在新的数组中的位置 赋值
                        newTab[e.hash & (newCap - 1)] = e;
                    else if (e instanceof TreeNode)
                        // 移动红黑树节点
                        ((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
                    else { // preserve order
                        // 普通的链表的移动
                        Node<K,V> loHead = null, loTail = null;
                        Node<K,V> hiHead = null, hiTail = null;
                        Node<K,V> next;
                        do {
                            next = e.next;
                            if ((e.hash & oldCap) == 0) {
                                if (loTail == null)
                                    loHead = e;
                                else
                                    loTail.next = e;
                                loTail = e;
                            }
                            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;
                        }
                        if (hiTail != null) {
                            hiTail.next = null;
                            newTab[j + oldCap] = hiHead;
                        }
                    }
                }
            }
        }
        return newTab;
    }