//存放元素的数组
transient volatile Node<K,V>[] table;
//数组中的Node节点
static class Node<K,V> implements Map.Entry<K,V> {final int hash;//Key计算出来的Hash值final K key;//Keyvolatile V val;//Valuevolatile Node<K,V> next;//链表的下一个节点
Node(int hash, K key, V val, Node<K,V> next) {this.hash = hash;this.key = key;this.val = val;this.next = next;}...//省略
    }
//红黑树中的节点
static final class TreeNode<K,V> extends Node<K,V> {TreeNode<K,V> parent;  // red-black tree linksTreeNode<K,V> left;       //左子节点TreeNode<K,V> right;    //右子节点TreeNode<K,V> prev;    //
        boolean red;...//省略
    }//组合TreeNode
static final class TreeBin<K,V> extends Node<K,V> {TreeNode<K,V> root;volatile TreeNode<K,V> first;}//内部类

 /** 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)tab = initTable();//初始化数组大小，默认16//数组指定位置元素为空，直接插入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
            }else if ((fh = f.hash) == MOVED)tab = helpTransfer(tab, f);else {//不为空，链表存储V oldVal = null;synchronized (f) {if (tabAt(tab, i) == f) {if (fh >= 0) {binCount = 1;for (Node<K,V> e = f;; ++binCount) {K ek;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;if ((e = e.next) == null) {pred.next = new Node<K,V>(hash, key,value, null);break;}}}//红黑树else if (f instanceof TreeBin) {Node<K,V> p;binCount = 2;if ((p = ((TreeBin<K,V>)f).putTreeVal(hash, key,value)) != null) {oldVal = p.val;if (!onlyIfAbsent)p.val = value;}}}}if (binCount != 0) {//链表长度大于8，转为红黑树存储if (binCount >= TREEIFY_THRESHOLD)treeifyBin(tab, i);if (oldVal != null)return oldVal;break;}}}addCount(1L, binCount);return null;}

/*** Replaces all linked nodes in bin at given index unless table is* too small, in which case resizes instead.*/private final void treeifyBin(Node<K,V>[] tab, int index) {Node<K,V> b; int n, sc;if (tab != null) {if ((n = tab.length) < MIN_TREEIFY_CAPACITY)tryPresize(n << 1);//扩容数组else if ((b = tabAt(tab, index)) != null && b.hash >= 0) {synchronized (b) {if (tabAt(tab, index) == b) {TreeNode<K,V> hd = null, tl = null;　　　　　　　　　　　　　　//遍历链表，构造TreeNodefor (Node<K,V> e = b; e != null; e = e.next) {TreeNode<K,V> p =new TreeNode<K,V>(e.hash, e.key, e.val,null, null);if ((p.prev = tl) == null)hd = p;elsetl.next = p;tl = p;}//构建红黑树setTabAt(tab, index, new TreeBin<K,V>(hd));}}}}}

 public V get(Object key) {Node<K,V>[] tab; Node<K,V> 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)//红黑树取值return (p = e.find(h, key)) != null ? p.val : null; //链表取值while ((e = e.next) != null) {if (e.hash == h &&((ek = e.key) == key || (ek != null && key.equals(ek))))return e.val;}}return null;}