HashMap.java

package java.util;

import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.Serializable;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Function;
import sun.misc.SharedSecrets;

public class HashMap<K, V> extends AbstractMap<K, V> implements Map<K, V>, Cloneable, Serializable
{

    private static final long serialVersionUID = 362498820763181265L;

    /**
     * 初始容量，必须是2的倍数
     */
    static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16

    /**
     * 最大容量，如果更高的值是由任何一个带有参数的构造函数隐式指定的，则使用该值。必须是2的倍数
     */
    static final int MAXIMUM_CAPACITY = 1 << 30;

    /**
     * 在构造函数中没有指定时使用的负载因子。
     */
    static final float DEFAULT_LOAD_FACTOR = 0.75f;

    /**
     * 使用tree而不是list的容器计数阈值。当向至少有这么多节点的bin中添加元素时，bin将被转换为tree。该值必须大于2，并且应该至少为8，以便与tree移除时关于收缩后转换回普通桶的假设相吻合。
     */
    static final int TREEIFY_THRESHOLD = 8;

    /**
     * The bin count threshold for untreeifying a (split) bin during a resize
     * operation. Should be less than TREEIFY_THRESHOLD, and at most 6 to mesh
     * with shrinkage detection under removal.
     */
    static final int UNTREEIFY_THRESHOLD = 6;

    /**
     * The smallest table capacity for which bins may be treeified. (Otherwise
     * the table is resized if too many nodes in a bin.) Should be at least 4 *
     * TREEIFY_THRESHOLD to avoid conflicts between resizing and treeification
     * thresholds. 可以对容器进行treeified的最小table
     * capacity。(否则，如果一个bin中有太多节点，就会重新调整table的大小。)至少4 *
     * TREEIFY_THRESHOLD，以避免调整大小和treeification阀值之间的冲突。
     */
    static final int MIN_TREEIFY_CAPACITY = 64;

    /**
     * Basic hash bin node, used for most entries. (See below for TreeNode
     * subclass, and in LinkedHashMap for its Entry subclass.)
     * 基本的哈希bin节点，用于大多数条目。(下面是TreeNode的子类，下面是LinkedHashMap的Entry子类。)
     */
    static class Node<K, V> implements Map.Entry<K, V>
    {
        final int hash;

        final K key;

        V value;

        Node<K, V> next;

        Node(int hash, K key, V value, Node<K, V> next)
        {
            this.hash = hash;
            this.key = key;
            this.value = value;
            this.next = next;
        }

        public final K getKey()
        {
            return key;
        }

        public final V getValue()
        {
            return value;
        }

        public final String toString()
        {
            return key + "=" + value;
        }

        public final int hashCode()
        {
            return Objects.hashCode(key) ^ Objects.hashCode(value);
        }

        public final V setValue(V newValue)
        {
            V oldValue = value;
            value = newValue;
            return oldValue;
        }

        public final boolean equals(Object o)
        {
            if (o == this)
                return true;
            if (o instanceof Map.Entry)
            {
                Map.Entry<?, ?> e = (Map.Entry<?, ?>)o;
                if (Objects.equals(key, e.getKey()) && Objects.equals(value, e.getValue()))
                    return true;
            }
            return false;
        }
    }

    /* ---------------- Static utilities -------------- */

    /*
     * 将hashcode高位和低位的值做异或运算进一步混淆，低位的信息中加入了高位的信息，这样做不但增加了复杂性，高位的信息也保留了下来。
     */
    static final int hash(Object key)
    {
        int h;
        return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
    }

    /**
     * Returns x's Class if it is of the form "class C implements
     * Comparable<C>", else null.
     */
    static Class<?> comparableClassFor(Object x)
    {
        if (x instanceof Comparable)
        {
            Class<?> c;
            Type[] ts, as;
            Type t;
            ParameterizedType p;
            if ((c = x.getClass()) == String.class) // bypass checks
                return c;
            if ((ts = c.getGenericInterfaces()) != null)
            {
                for (int i = 0; i < ts.length; ++i)
                {
                    if (((t = ts[i]) instanceof ParameterizedType)
                            && ((p = (ParameterizedType)t).getRawType() == Comparable.class)
                            && (as = p.getActualTypeArguments()) != null && as.length == 1 && as[0] == c) // type
                                                                                                          // arg
                                                                                                          // is
                                                                                                          // c
                        return c;
                }
            }
        }
        return null;
    }

    /**
     * Returns k.compareTo(x) if x matches kc (k's screened comparable class),
     * else 0.
     */
    @SuppressWarnings ({"rawtypes", "unchecked"}) // for cast to Comparable
    static int compareComparables(Class<?> kc, Object k, Object x)
    {
        return (x == null || x.getClass() != kc ? 0 : ((Comparable)k).compareTo(x));
    }

    /**
     * 保证返回的值是2的幂，即当cap是1-2-4-8-16-32...之间的任意数，（*2^N< cap <2^N+1）,返回值为2^N+1。 int
     * n = cap - 1; 作用：保证当cap为2的幂时，返回原值而不是二倍，如8 返回8 而不是16
     */
    static final int tableSizeFor(int cap)
    {
        int n = cap - 1; // 作用：保证当cap为2的幂时，返回原值而不是二倍，如8 返回8 而不是16
        n |= n >>> 1;
        n |= n >>> 2;
        n |= n >>> 4;
        n |= n >>> 8;
        n |= n >>> 16;
        return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
    }

    /* ---------------- Fields -------------- */

    /**
     * table，第一次使用时初始化，并根据需要调整大小。当分配时，长度总是2的幂。(在某些操作中，我们还允许长度为零，以允许当前不需要的引导机制。)
     * 实际存储key，value的数组，只不过key，value被封装成Node了
     */
    transient Node<K, V>[] table;

    /**
     * H保存缓存entrySet().注意，AbstractMap字段（ 域）用于keySet()和values()。
     */
    transient Set<Map.Entry<K, V>> entrySet;

    /**
     * 此map中包含的键-值映射的数目。
     */
    transient int size;

    /**
     * 结构修改次数
     */
    transient int modCount;

    /**
     * 要调整大小的下一个大小值(容量*负载因子)。 The javadoc description is true upon
     * serialization.Additionally, if the table array has not been allocated,
     * this field holds the initial array capacity, or zero signifying
     * DEFAULT_INITIAL_CAPACITY.)
     */
    int threshold;

    final float loadFactor;

    /* ---------------- Public operations -------------- */

    public HashMap(int initialCapacity, float loadFactor)
    {
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal initial capacity: " + initialCapacity);
        if (initialCapacity > MAXIMUM_CAPACITY)
            initialCapacity = MAXIMUM_CAPACITY;
        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new IllegalArgumentException("Illegal load factor: " + loadFactor);
        this.loadFactor = loadFactor;
        this.threshold = tableSizeFor(initialCapacity);
    }

    public HashMap(int initialCapacity)
    {
        this(initialCapacity, DEFAULT_LOAD_FACTOR);
    }

    /**
     * 构造一个空的HashMap，默认初始容量(16)和默认负载因子(0.75)。
     */
    public HashMap()
    {
        this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
    }

    public HashMap(Map<? extends K, ? extends V> m)
    {
        this.loadFactor = DEFAULT_LOAD_FACTOR;
        putMapEntries(m, false);
    }

    final void putMapEntries(Map<? extends K, ? extends V> m, boolean evict)
    {
        int s = m.size();
        if (s > 0)
        {
            if (table == null)
            { // 计算容量
                float ft = ((float)s / loadFactor) + 1.0F;
                int t = ((ft < (float)MAXIMUM_CAPACITY) ? (int)ft : MAXIMUM_CAPACITY);
                if (t > threshold)
                    threshold = tableSizeFor(t); // 设置下一个扩容容量值·
            }
            else if (s > threshold)
                resize(); // 如果大于threshold 则先扩容
            for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
            {
                K key = e.getKey();
                V value = e.getValue();
                putVal(hash(key), key, value, false, evict);
            }
        }
    }

    public int size()
    {
        return size;
    }

    public boolean isEmpty()
    {
        return size == 0;
    }

    public V get(Object key)
    {
        Node<K, V> e;
        return (e = getNode(hash(key), key)) == null ? null : e.value;
    }

    final Node<K, V> getNode(int hash, Object key)
    {
        Node<K, V>[] tab;
        Node<K, V> first, e;
        int n;
        K k;
        if ((tab = table) != null && (n = tab.length) > 0 && (first = tab[(n - 1) & hash]) != null)
        {
            // 先判断第一个节点
            if (first.hash == hash && // always check first node
                    ((k = first.key) == key || (key != null && key.equals(k))))
                return first;
            if ((e = first.next) != null)
            {
                // 若是树
                if (first instanceof TreeNode)
                    return ((TreeNode<K, V>)first).getTreeNode(hash, key);
                // 链表
                do
                {
                    if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
                        return e;
                } while ((e = e.next) != null);
            }
        }
        return null;
    }

    public boolean containsKey(Object key)
    {
        return getNode(hash(key), key) != null;
    }

    /**
     * 将指定值与此Map中的指定键关联。如果Map之前包含键的映射，则替换旧值。
     */
    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)
            n = (tab = resize()).length;
        // 为空直接赋值
        if ((p = tab[i = (n - 1) & hash]) == null)
            tab[i] = newNode(hash, key, value, null);
        else
        {
            Node<K, V> e;
            K k;
            // 单节点直接赋值
            if (p.hash == hash && ((k = p.key) == key || (key != null && key.equals(k))))
                e = p;
            // 树节点走树节点逻辑
            else if (p instanceof TreeNode)
                e = ((TreeNode<K, V>)p).putTreeVal(this, tab, hash, key, value);
            // 链表节点走链表节点逻辑
            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
                            // 链表过长转红黑树
                            treeifyBin(tab, hash);
                        break;
                    }
                    if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
                        break;
                    p = e;
                }
            }
            // 不为空替换旧值
            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;
    }

    /**
     * 初始化或加倍表大小。如果为空，则按照字段阈值中持有的初始容量目标分配。否则，因为我们使用的是2的幂展开，所以每个bin中的元素必须保持相同的索引，或者在新表中以2的幂偏移移动。
     *
     * @return the table
     */
    final Node<K, V>[] resize()
    {
        Node<K, V>[] oldTab = table;
        int oldCap = (oldTab == null) ? 0 : oldTab.length;
        int oldThr = threshold;
        int newCap, newThr = 0;
        /*
         * 如果oldCap > 0 说明table非null， oldCap为原table大小，oldThr为原阈值大小 = oldCap *
         * loadFactor
         */
        if (oldCap > 0)
        {
            // 如果oldcap大于最大值，阈值直接等于int最大值，当前resize操作执行不了直接返回，以后也不会再扩容
            if (oldCap >= MAXIMUM_CAPACITY)
            {
                threshold = Integer.MAX_VALUE;
                return oldTab;
            }
            // 新容量为原来的二倍
            else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY && oldCap >= DEFAULT_INITIAL_CAPACITY)
                newThr = oldThr << 1; // double threshold
        }

        /*
         * 走到这说明oldCap <= 0,若此时oldThr > 0 充分说明此时hashMap是一个 table为空，threshold > 0
         * 的初始状态（调用构造函数 HashMap(int initialCapacity, float loadFactor) 或
         * HashMap(int initialCapacity) 或 HashMap(Map<? extends K, ? extends V>
         * m)，导致 table 为 null，Cap为0， threshold为用户指定的
         * HashMap的初始容量），此时根据初始阈值直接初始化容量
         */
        else if (oldThr > 0) // initial capacity was placed in threshold
            newCap = oldThr;
        /*
         * 走到这说明oldCap <= 0 oldThr <= 0,
         * 此时hashMap处于使用HashMap()构造函数初始化的状态，Cap为0，thrrshold为0
         */
        else
        { // zero initial threshold signifies using defaults
            newCap = DEFAULT_INITIAL_CAPACITY;
            newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
        }
        // 如果新阈值为 0 ， 创建新阈值
        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"})
        Node<K, V>[] newTab = (Node<K, V>[])new Node[newCap];
        table = newTab;
        if (oldTab != null)
        {
            for (int j = 0; j < oldCap; ++j)
            {
                Node<K, V> e;
                if ((e = oldTab[j]) != null)
                {
                    // 释放资源
                    oldTab[j] = null;
                    // 若是单节点直接在newTab中重新定位
                    if (e.next == null)
                        newTab[e.hash & (newCap - 1)] = e;
                    // 若节点是TreeNode节点，要进行 红黑树的 rehash操作
                    else if (e instanceof TreeNode)
                        ((TreeNode<K, V>)e).split(this, newTab, j, oldCap);
                    // 若节点是链表，进行链表的rehash操作
                    else
                    { // preserve order
                        Node<K, V> loHead = null, loTail = null;
                        Node<K, V> hiHead = null, hiTail = null;
                        Node<K, V> next;
                        do
                        {
                            next = e.next;
                            // 将同一桶中的元素根据(e.hash & oldCap)是否为0进行分割
                            // 根据算法 e.hash & oldCap 判断节点位置rehash 后是否发生改变
                            // 最高位==0，这是索引不变的链表。
                            if ((e.hash & oldCap) == 0)
                            {
                                if (loTail == null)
                                    loHead = e;
                                else
                                    loTail.next = e;
                                loTail = e;
                            }
                            // 最高位==1 （这是索引发生改变的链表）
                            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;
    }

    /**
     * Replaces all linked nodes in bin at index for given hash unless table is
     * too small, in which case resizes instead.
     */
    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
            {
                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);
        }
    }

    public void putAll(Map<? extends K, ? extends V> m)
    {
        putMapEntries(m, true);
    }

    public V remove(Object key)
    {
        Node<K, V> e;
        return (e = removeNode(hash(key), key, null, false, true)) == null ? null : e.value;
    }

    /*
     * 移除和添加类似
     */
    final Node<K, V> removeNode(int hash, Object key, Object value, boolean matchValue, boolean movable)
    {
        Node<K, V>[] tab;
        Node<K, V> p;
        int n, index;
        if ((tab = table) != null && (n = tab.length) > 0 && (p = tab[index = (n - 1) & hash]) != null)
        {
            Node<K, V> node = null, e;
            K k;
            V v;
            if (p.hash == hash && ((k = p.key) == key || (key != null && key.equals(k))))
                node = p;
            else if ((e = p.next) != null)
            {
                if (p instanceof TreeNode)
                    node = ((TreeNode<K, V>)p).getTreeNode(hash, key);
                else
                {
                    do
                    {
                        if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
                        {
                            node = e;
                            break;
                        }
                        p = e;
                    } while ((e = e.next) != null);
                }
            }
            if (node != null && (!matchValue || (v = node.value) == value || (value != null && value.equals(v))))
            {
                if (node instanceof TreeNode)
                    ((TreeNode<K, V>)node).removeTreeNode(this, tab, movable);
                else if (node == p)
                    tab[index] = node.next;
                else
                    p.next = node.next;
                ++modCount;
                --size;
                afterNodeRemoval(node);
                return node;
            }
        }
        return null;
    }

    public void clear()
    {
        Node<K, V>[] tab;
        modCount++;
        if ((tab = table) != null && size > 0)
        {
            size = 0;
            for (int i = 0; i < tab.length; ++i)
                tab[i] = null;
        }
    }

    public boolean containsValue(Object value)
    {
        Node<K, V>[] tab;
        V v;
        if ((tab = table) != null && size > 0)
        {
            // 遍历table
            for (int i = 0; i < tab.length; ++i)
            {
                // 遍历节点
                for (Node<K, V> e = tab[i]; e != null; e = e.next)
                {
                    if ((v = e.value) == value || (value != null && value.equals(v)))
                        return true;
                }
            }
        }
        return false;
    }

    public Set<K> keySet()
    {
        Set<K> ks = keySet;
        if (ks == null)
        {
            ks = new KeySet();
            keySet = ks;
        }
        return ks;
    }

    final class KeySet extends AbstractSet<K>
    {
        public final int size()
        {
            return size;
        }

        public final void clear()
        {
            HashMap.this.clear();
        }

        public final Iterator<K> iterator()
        {
            return new KeyIterator();
        }

        public final boolean contains(Object o)
        {
            return containsKey(o);
        }

        public final boolean remove(Object key)
        {
            return removeNode(hash(key), key, null, false, true) != null;
        }

        public final Spliterator<K> spliterator()
        {
            return new KeySpliterator<>(HashMap.this, 0, -1, 0, 0);
        }

        public final void forEach(Consumer<? super K> action)
        {
            Node<K, V>[] tab;
            if (action == null)
                throw new NullPointerException();
            if (size > 0 && (tab = table) != null)
            {
                int mc = modCount;
                for (int i = 0; i < tab.length; ++i)
                {
                    for (Node<K, V> e = tab[i]; e != null; e = e.next)
                        action.accept(e.key);
                }
                if (modCount != mc)
                    throw new ConcurrentModificationException();
            }
        }
    }

    public Collection<V> values()
    {
        Collection<V> vs = values;
        if (vs == null)
        {
            vs = new Values();
            values = vs;
        }
        return vs;
    }

    final class Values extends AbstractCollection<V>
    {
        public final int size()
        {
            return size;
        }

        public final void clear()
        {
            HashMap.this.clear();
        }

        public final Iterator<V> iterator()
        {
            return new ValueIterator();
        }

        public final boolean contains(Object o)
        {
            return containsValue(o);
        }

        public final Spliterator<V> spliterator()
        {
            return new ValueSpliterator<>(HashMap.this, 0, -1, 0, 0);
        }

        public final void forEach(Consumer<? super V> action)
        {
            Node<K, V>[] tab;
            if (action == null)
                throw new NullPointerException();
            if (size > 0 && (tab = table) != null)
            {
                int mc = modCount;
                for (int i = 0; i < tab.length; ++i)
                {
                    for (Node<K, V> e = tab[i]; e != null; e = e.next)
                        action.accept(e.value);
                }
                if (modCount != mc)
                    throw new ConcurrentModificationException();
            }
        }
    }

    public Set<Map.Entry<K, V>> entrySet()
    {
        Set<Map.Entry<K, V>> es;
        return (es = entrySet) == null ? (entrySet = new EntrySet()) : es;
    }

    final class EntrySet extends AbstractSet<Map.Entry<K, V>>
    {
        public final int size()
        {
            return size;
        }

        public final void clear()
        {
            HashMap.this.clear();
        }

        public final Iterator<Map.Entry<K, V>> iterator()
        {
            return new EntryIterator();
        }

        public final boolean contains(Object o)
        {
            if (!(o instanceof Map.Entry))
                return false;
            Map.Entry<?, ?> e = (Map.Entry<?, ?>)o;
            Object key = e.getKey();
            Node<K, V> candidate = getNode(hash(key), key);
            return candidate != null && candidate.equals(e);
        }

        public final boolean remove(Object o)
        {
            if (o instanceof Map.Entry)
            {
                Map.Entry<?, ?> e = (Map.Entry<?, ?>)o;
                Object key = e.getKey();
                Object value = e.getValue();
                return removeNode(hash(key), key, value, true, true) != null;
            }
            return false;
        }

        public final Spliterator<Map.Entry<K, V>> spliterator()
        {
            return new EntrySpliterator<>(HashMap.this, 0, -1, 0, 0);
        }

        public final void forEach(Consumer<? super Map.Entry<K, V>> action)
        {
            Node<K, V>[] tab;
            if (action == null)
                throw new NullPointerException();
            if (size > 0 && (tab = table) != null)
            {
                int mc = modCount;
                for (int i = 0; i < tab.length; ++i)
                {
                    for (Node<K, V> e = tab[i]; e != null; e = e.next)
                        action.accept(e);
                }
                if (modCount != mc)
                    throw new ConcurrentModificationException();
            }
        }
    }

    // Overrides of JDK8 Map extension methods

    @Override
    public V getOrDefault(Object key, V defaultValue)
    {
        Node<K, V> e;
        return (e = getNode(hash(key), key)) == null ? defaultValue : e.value;
    }

    @Override
    public V putIfAbsent(K key, V value)
    {
        return putVal(hash(key), key, value, true, true);
    }

    @Override
    public boolean remove(Object key, Object value)
    {
        return removeNode(hash(key), key, value, true, true) != null;
    }

    @Override
    public boolean replace(K key, V oldValue, V newValue)
    {
        Node<K, V> e;
        V v;
        if ((e = getNode(hash(key), key)) != null && ((v = e.value) == oldValue || (v != null && v.equals(oldValue))))
        {
            e.value = newValue;
            afterNodeAccess(e);
            return true;
        }
        return false;
    }

    @Override
    public V replace(K key, V value)
    {
        Node<K, V> e;
        if ((e = getNode(hash(key), key)) != null)
        {
            V oldValue = e.value;
            e.value = value;
            afterNodeAccess(e);
            return oldValue;
        }
        return null;
    }

    @Override
    public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction)
    {
        if (mappingFunction == null)
            throw new NullPointerException();
        int hash = hash(key);
        Node<K, V>[] tab;
        Node<K, V> first;
        int n, i;
        int binCount = 0;
        TreeNode<K, V> t = null;
        Node<K, V> old = null;
        if (size > threshold || (tab = table) == null || (n = tab.length) == 0)
            n = (tab = resize()).length;
        if ((first = tab[i = (n - 1) & hash]) != null)
        {
            // 红黑树
            if (first instanceof TreeNode)
                old = (t = (TreeNode<K, V>)first).getTreeNode(hash, key);
            else
            {
                // 链表
                Node<K, V> e = first;
                K k;
                do
                {
                    if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
                    {
                        old = e;
                        break;
                    }
                    ++binCount;
                } while ((e = e.next) != null);
            }
            V oldValue;
            if (old != null && (oldValue = old.value) != null)
            {
                afterNodeAccess(old);
                return oldValue;
            }
        }
        // 计算
        V v = mappingFunction.apply(key);
        if (v == null)
        {
            return null;
        }
        // 链表
        else if (old != null)
        {
            old.value = v;
            afterNodeAccess(old);
            return v;
        }
        // 树
        else if (t != null)
            t.putTreeVal(this, tab, hash, key, v);
        else
        {
            tab[i] = newNode(hash, key, v, first);
            if (binCount >= TREEIFY_THRESHOLD - 1)
                treeifyBin(tab, hash);
        }
        ++modCount;
        ++size;
        afterNodeInsertion(true);
        return v;
    }

    public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)
    {
        if (remappingFunction == null)
            throw new NullPointerException();
        Node<K, V> e;
        V oldValue;
        int hash = hash(key);
        if ((e = getNode(hash, key)) != null && (oldValue = e.value) != null)
        {
            V v = remappingFunction.apply(key, oldValue);
            if (v != null)
            {
                e.value = v;
                afterNodeAccess(e);
                return v;
            }
            // =null直接移除？
            else
                removeNode(hash, key, null, false, true);
        }
        return null;
    }

    @Override
    public V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)
    {
        if (remappingFunction == null)
            throw new NullPointerException();
        int hash = hash(key);
        Node<K, V>[] tab;
        Node<K, V> first;
        int n, i;
        int binCount = 0;
        TreeNode<K, V> t = null;
        Node<K, V> old = null;
        if (size > threshold || (tab = table) == null || (n = tab.length) == 0)
            n = (tab = resize()).length;
        if ((first = tab[i = (n - 1) & hash]) != null)
        {
            if (first instanceof TreeNode)
                old = (t = (TreeNode<K, V>)first).getTreeNode(hash, key);
            else
            {
                Node<K, V> e = first;
                K k;
                do
                {
                    if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
                    {
                        old = e;
                        break;
                    }
                    ++binCount;
                } while ((e = e.next) != null);
            }
        }
        V oldValue = (old == null) ? null : old.value;
        V v = remappingFunction.apply(key, oldValue);
        if (old != null)
        {
            if (v != null)
            {
                old.value = v;
                afterNodeAccess(old);
            }
            else
                removeNode(hash, key, null, false, true);
        }
        else if (v != null)
        {
            if (t != null)
                t.putTreeVal(this, tab, hash, key, v);
            else
            {
                tab[i] = newNode(hash, key, v, first);
                if (binCount >= TREEIFY_THRESHOLD - 1)
                    treeifyBin(tab, hash);
            }
            ++modCount;
            ++size;
            afterNodeInsertion(true);
        }
        return v;
    }

    @Override
    public V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction)
    {
        if (value == null)
            throw new NullPointerException();
        if (remappingFunction == null)
            throw new NullPointerException();
        int hash = hash(key);
        Node<K, V>[] tab;
        Node<K, V> first;
        int n, i;
        int binCount = 0;
        TreeNode<K, V> t = null;
        Node<K, V> old = null;
        if (size > threshold || (tab = table) == null || (n = tab.length) == 0)
            n = (tab = resize()).length;
        if ((first = tab[i = (n - 1) & hash]) != null)
        {
            if (first instanceof TreeNode)
                old = (t = (TreeNode<K, V>)first).getTreeNode(hash, key);
            else
            {
                Node<K, V> e = first;
                K k;
                do
                {
                    if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
                    {
                        old = e;
                        break;
                    }
                    ++binCount;
                } while ((e = e.next) != null);
            }
        }
        if (old != null)
        {
            V v;
            if (old.value != null)
                v = remappingFunction.apply(old.value, value);
            else
                v = value;
            if (v != null)
            {
                old.value = v;
                afterNodeAccess(old);
            }
            else
                removeNode(hash, key, null, false, true);
            return v;
        }
        if (value != null)
        {
            if (t != null)
                t.putTreeVal(this, tab, hash, key, value);
            else
            {
                tab[i] = newNode(hash, key, value, first);
                if (binCount >= TREEIFY_THRESHOLD - 1)
                    treeifyBin(tab, hash);
            }
            ++modCount;
            ++size;
            afterNodeInsertion(true);
        }
        return value;
    }

    @Override
    public void forEach(BiConsumer<? super K, ? super V> action)
    {
        Node<K, V>[] tab;
        if (action == null)
            throw new NullPointerException();
        if (size > 0 && (tab = table) != null)
        {
            int mc = modCount;
            for (int i = 0; i < tab.length; ++i)
            {
                for (Node<K, V> e = tab[i]; e != null; e = e.next)
                    action.accept(e.key, e.value);
            }
            if (modCount != mc)
                throw new ConcurrentModificationException();
        }
    }

    @Override
    public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function)
    {
        Node<K, V>[] tab;
        if (function == null)
            throw new NullPointerException();
        if (size > 0 && (tab = table) != null)
        {
            int mc = modCount;
            for (int i = 0; i < tab.length; ++i)
            {
                for (Node<K, V> e = tab[i]; e != null; e = e.next)
                {
                    e.value = function.apply(e.key, e.value);
                }
            }
            if (modCount != mc)
                throw new ConcurrentModificationException();
        }
    }

    /* ------------------------------------------------------------ */
    // Cloning and serialization

    /**
     * Returns a shallow copy of this <tt>HashMap</tt> instance: the keys and
     * values themselves are not cloned.
     *
     * @return a shallow copy of this map
     */
    @SuppressWarnings ("unchecked")
    @Override
    public Object clone()
    {
        HashMap<K, V> result;
        try
        {
            result = (HashMap<K, V>)super.clone();
        }
        catch (CloneNotSupportedException e)
        {
            // this shouldn't happen, since we are Cloneable
            throw new InternalError(e);
        }
        result.reinitialize();
        result.putMapEntries(this, false);
        return result;
    }

    // These methods are also used when serializing HashSets
    final float loadFactor()
    {
        return loadFactor;
    }

    final int capacity()
    {
        return (table != null) ? table.length : (threshold > 0) ? threshold : DEFAULT_INITIAL_CAPACITY;
    }

    private void writeObject(java.io.ObjectOutputStream s) throws IOException
    {
        int buckets = capacity();
        // Write out the threshold, loadfactor, and any hidden stuff
        s.defaultWriteObject();
        s.writeInt(buckets);
        s.writeInt(size);
        internalWriteEntries(s);
    }

    private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException
    {
        // Read in the threshold (ignored), loadfactor, and any hidden stuff
        s.defaultReadObject();
        reinitialize();
        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new InvalidObjectException("Illegal load factor: " + loadFactor);
        s.readInt(); // Read and ignore number of buckets
        int mappings = s.readInt(); // Read number of mappings (size)
        if (mappings < 0)
            throw new InvalidObjectException("Illegal mappings count: " + mappings);
        else if (mappings > 0)
        { // (if zero, use defaults)
          // Size the table using given load factor only if within
          // range of 0.25...4.0
            float lf = Math.min(Math.max(0.25f, loadFactor), 4.0f);
            float fc = (float)mappings / lf + 1.0f;
            int cap = ((fc < DEFAULT_INITIAL_CAPACITY) ? DEFAULT_INITIAL_CAPACITY
                    : (fc >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : tableSizeFor((int)fc));
            float ft = (float)cap * lf;
            threshold = ((cap < MAXIMUM_CAPACITY && ft < MAXIMUM_CAPACITY) ? (int)ft : Integer.MAX_VALUE);

            // Check Map.Entry[].class since it's the nearest public type to
            // what we're actually creating.
            SharedSecrets.getJavaOISAccess().checkArray(s, Map.Entry[].class, cap);
            @SuppressWarnings ({"rawtypes", "unchecked"})
            Node<K, V>[] tab = (Node<K, V>[])new Node[cap];
            table = tab;

            // Read the keys and values, and put the mappings in the HashMap
            for (int i = 0; i < mappings; i++)
            {
                @SuppressWarnings ("unchecked")
                K key = (K)s.readObject();
                @SuppressWarnings ("unchecked")
                V value = (V)s.readObject();
                putVal(hash(key), key, value, false, false);
            }
        }
    }

    /* ------------------------------------------------------------ */
    // iterators

    abstract class HashIterator
    {
        Node<K, V> next; // next entry to return

        Node<K, V> current; // current entry

        int expectedModCount; // for fast-fail

        int index; // current slot

        HashIterator()
        {
            expectedModCount = modCount;
            Node<K, V>[] t = table;
            current = next = null;
            index = 0;
            if (t != null && size > 0)
            { // advance to first entry
                do
                {} while (index < t.length && (next = t[index++]) == null);
            }
        }

        public final boolean hasNext()
        {
            return next != null;
        }

        final Node<K, V> nextNode()
        {
            Node<K, V>[] t;
            Node<K, V> e = next;
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            if (e == null)
                throw new NoSuchElementException();
            if ((next = (current = e).next) == null && (t = table) != null)
            {
                do
                {} while (index < t.length && (next = t[index++]) == null);
            }
            return e;
        }

        public final void remove()
        {
            Node<K, V> p = current;
            if (p == null)
                throw new IllegalStateException();
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            current = null;
            K key = p.key;
            removeNode(hash(key), key, null, false, false);
            expectedModCount = modCount;
        }
    }

    final class KeyIterator extends HashIterator implements Iterator<K>
    {
        public final K next()
        {
            return nextNode().key;
        }
    }

    final class ValueIterator extends HashIterator implements Iterator<V>
    {
        public final V next()
        {
            return nextNode().value;
        }
    }

    final class EntryIterator extends HashIterator implements Iterator<Map.Entry<K, V>>
    {
        public final Map.Entry<K, V> next()
        {
            return nextNode();
        }
    }

    /* ------------------------------------------------------------ */
    // spliterators

    static class HashMapSpliterator<K, V>
    {
        final HashMap<K, V> map;

        Node<K, V> current; // current node

        int index; // current index, modified on advance/split

        int fence; // one past last index

        int est; // size estimate

        int expectedModCount; // for comodification checks

        HashMapSpliterator(HashMap<K, V> m, int origin, int fence, int est, int expectedModCount)
        {
            this.map = m;
            this.index = origin;
            this.fence = fence;
            this.est = est;
            this.expectedModCount = expectedModCount;
        }

        final int getFence()
        { // initialize fence and size on first use
            int hi;
            if ((hi = fence) < 0)
            {
                HashMap<K, V> m = map;
                est = m.size;
                expectedModCount = m.modCount;
                Node<K, V>[] tab = m.table;
                hi = fence = (tab == null) ? 0 : tab.length;
            }
            return hi;
        }

        public final long estimateSize()
        {
            getFence(); // force init
            return (long)est;
        }
    }

    static final class KeySpliterator<K, V> extends HashMapSpliterator<K, V> implements Spliterator<K>
    {
        KeySpliterator(HashMap<K, V> m, int origin, int fence, int est, int expectedModCount)
        {
            super(m, origin, fence, est, expectedModCount);
        }

        public KeySpliterator<K, V> trySplit()
        {
            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
            return (lo >= mid || current != null) ? null
                    : new KeySpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount);
        }

        public void forEachRemaining(Consumer<? super K> action)
        {
            int i, hi, mc;
            if (action == null)
                throw new NullPointerException();
            HashMap<K, V> m = map;
            Node<K, V>[] tab = m.table;
            if ((hi = fence) < 0)
            {
                mc = expectedModCount = m.modCount;
                hi = fence = (tab == null) ? 0 : tab.length;
            }
            else
                mc = expectedModCount;
            if (tab != null && tab.length >= hi && (i = index) >= 0 && (i < (index = hi) || current != null))
            {
                Node<K, V> p = current;
                current = null;
                do
                {
                    if (p == null)
                        p = tab[i++];
                    else
                    {
                        action.accept(p.key);
                        p = p.next;
                    }
                } while (p != null || i < hi);
                if (m.modCount != mc)
                    throw new ConcurrentModificationException();
            }
        }

        public boolean tryAdvance(Consumer<? super K> action)
        {
            int hi;
            if (action == null)
                throw new NullPointerException();
            Node<K, V>[] tab = map.table;
            if (tab != null && tab.length >= (hi = getFence()) && index >= 0)
            {
                while (current != null || index < hi)
                {
                    if (current == null)
                        current = tab[index++];
                    else
                    {
                        K k = current.key;
                        current = current.next;
                        action.accept(k);
                        if (map.modCount != expectedModCount)
                            throw new ConcurrentModificationException();
                        return true;
                    }
                }
            }
            return false;
        }

        public int characteristics()
        {
            return (fence < 0 || est == map.size ? Spliterator.SIZED : 0) | Spliterator.DISTINCT;
        }
    }

    static final class ValueSpliterator<K, V> extends HashMapSpliterator<K, V> implements Spliterator<V>
    {
        ValueSpliterator(HashMap<K, V> m, int origin, int fence, int est, int expectedModCount)
        {
            super(m, origin, fence, est, expectedModCount);
        }

        public ValueSpliterator<K, V> trySplit()
        {
            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
            return (lo >= mid || current != null) ? null
                    : new ValueSpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount);
        }

        public void forEachRemaining(Consumer<? super V> action)
        {
            int i, hi, mc;
            if (action == null)
                throw new NullPointerException();
            HashMap<K, V> m = map;
            Node<K, V>[] tab = m.table;
            if ((hi = fence) < 0)
            {
                mc = expectedModCount = m.modCount;
                hi = fence = (tab == null) ? 0 : tab.length;
            }
            else
                mc = expectedModCount;
            if (tab != null && tab.length >= hi && (i = index) >= 0 && (i < (index = hi) || current != null))
            {
                Node<K, V> p = current;
                current = null;
                do
                {
                    if (p == null)
                        p = tab[i++];
                    else
                    {
                        action.accept(p.value);
                        p = p.next;
                    }
                } while (p != null || i < hi);
                if (m.modCount != mc)
                    throw new ConcurrentModificationException();
            }
        }

        public boolean tryAdvance(Consumer<? super V> action)
        {
            int hi;
            if (action == null)
                throw new NullPointerException();
            Node<K, V>[] tab = map.table;
            if (tab != null && tab.length >= (hi = getFence()) && index >= 0)
            {
                while (current != null || index < hi)
                {
                    if (current == null)
                        current = tab[index++];
                    else
                    {
                        V v = current.value;
                        current = current.next;
                        action.accept(v);
                        if (map.modCount != expectedModCount)
                            throw new ConcurrentModificationException();
                        return true;
                    }
                }
            }
            return false;
        }

        public int characteristics()
        {
            return (fence < 0 || est == map.size ? Spliterator.SIZED : 0);
        }
    }

    static final class EntrySpliterator<K, V> extends HashMapSpliterator<K, V> implements Spliterator<Map.Entry<K, V>>
    {
        EntrySpliterator(HashMap<K, V> m, int origin, int fence, int est, int expectedModCount)
        {
            super(m, origin, fence, est, expectedModCount);
        }

        public EntrySpliterator<K, V> trySplit()
        {
            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
            return (lo >= mid || current != null) ? null
                    : new EntrySpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount);
        }

        public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action)
        {
            int i, hi, mc;
            if (action == null)
                throw new NullPointerException();
            HashMap<K, V> m = map;
            Node<K, V>[] tab = m.table;
            if ((hi = fence) < 0)
            {
                mc = expectedModCount = m.modCount;
                hi = fence = (tab == null) ? 0 : tab.length;
            }
            else
                mc = expectedModCount;
            if (tab != null && tab.length >= hi && (i = index) >= 0 && (i < (index = hi) || current != null))
            {
                Node<K, V> p = current;
                current = null;
                do
                {
                    if (p == null)
                        p = tab[i++];
                    else
                    {
                        action.accept(p);
                        p = p.next;
                    }
                } while (p != null || i < hi);
                if (m.modCount != mc)
                    throw new ConcurrentModificationException();
            }
        }

        public boolean tryAdvance(Consumer<? super Map.Entry<K, V>> action)
        {
            int hi;
            if (action == null)
                throw new NullPointerException();
            Node<K, V>[] tab = map.table;
            if (tab != null && tab.length >= (hi = getFence()) && index >= 0)
            {
                while (current != null || index < hi)
                {
                    if (current == null)
                        current = tab[index++];
                    else
                    {
                        Node<K, V> e = current;
                        current = current.next;
                        action.accept(e);
                        if (map.modCount != expectedModCount)
                            throw new ConcurrentModificationException();
                        return true;
                    }
                }
            }
            return false;
        }

        public int characteristics()
        {
            return (fence < 0 || est == map.size ? Spliterator.SIZED : 0) | Spliterator.DISTINCT;
        }
    }

    /* ------------------------------------------------------------ */
    // LinkedHashMap support

    /*
     * The following package-protected methods are designed to be overridden by
     * LinkedHashMap, but not by any other subclass. Nearly all other internal
     * methods are also package-protected but are declared final, so can be used
     * by LinkedHashMap, view classes, and HashSet.
     */

    // Create a regular (non-tree) node
    Node<K, V> newNode(int hash, K key, V value, Node<K, V> next)
    {
        return new Node<>(hash, key, value, next);
    }

    // For conversion from TreeNodes to plain nodes
    Node<K, V> replacementNode(Node<K, V> p, Node<K, V> next)
    {
        return new Node<>(p.hash, p.key, p.value, next);
    }

    // Create a tree bin node
    TreeNode<K, V> newTreeNode(int hash, K key, V value, Node<K, V> next)
    {
        return new TreeNode<>(hash, key, value, next);
    }

    // For treeifyBin
    TreeNode<K, V> replacementTreeNode(Node<K, V> p, Node<K, V> next)
    {
        return new TreeNode<>(p.hash, p.key, p.value, next);
    }

    /**
     * Reset to initial default state. Called by clone and readObject.
     */
    void reinitialize()
    {
        table = null;
        entrySet = null;
        keySet = null;
        values = null;
        modCount = 0;
        threshold = 0;
        size = 0;
    }

    // Callbacks to allow LinkedHashMap post-actions
    void afterNodeAccess(Node<K, V> p)
    {}

    void afterNodeInsertion(boolean evict)
    {}

    void afterNodeRemoval(Node<K, V> p)
    {}

    // Called only from writeObject, to ensure compatible ordering.
    void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException
    {
        Node<K, V>[] tab;
        if (size > 0 && (tab = table) != null)
        {
            for (int i = 0; i < tab.length; ++i)
            {
                for (Node<K, V> e = tab[i]; e != null; e = e.next)
                {
                    s.writeObject(e.key);
                    s.writeObject(e.value);
                }
            }
        }
    }

    /* ------------------------------------------------------------ */
    // Tree bins

    /**
     * Entry for Tree bins. Extends LinkedHashMap.Entry (which in turn extends
     * Node) so can be used as extension of either regular or linked node.
     */
    static final class TreeNode<K, V> extends LinkedHashMap.Entry<K, V>
    {
        TreeNode<K, V> parent; // red-black tree links

        TreeNode<K, V> left;

        TreeNode<K, V> right;

        TreeNode<K, V> prev; // needed to unlink next upon deletion

        boolean red;

        TreeNode(int hash, K key, V val, Node<K, V> next)
        {
            super(hash, key, val, next);
        }

        /**
         * Returns root of tree containing this node.
         */
        final TreeNode<K, V> root()
        {
            for (TreeNode<K, V> r = this, p;;)
            {
                if ((p = r.parent) == null)
                    return r;
                r = p;
            }
        }

        /**
         * Ensures that the given root is the first node of its bin.
         */
        static <K, V> void moveRootToFront(Node<K, V>[] tab, TreeNode<K, V> root)
        {
            int n;
            if (root != null && tab != null && (n = tab.length) > 0)
            {
                int index = (n - 1) & root.hash;
                TreeNode<K, V> first = (TreeNode<K, V>)tab[index];
                if (root != first)
                {
                    Node<K, V> rn;
                    tab[index] = root;
                    TreeNode<K, V> rp = root.prev;
                    if ((rn = root.next) != null)
                        ((TreeNode<K, V>)rn).prev = rp;
                    if (rp != null)
                        rp.next = rn;
                    if (first != null)
                        first.prev = root;
                    root.next = first;
                    root.prev = null;
                }
                assert checkInvariants(root);
            }
        }

        /**
         * Finds the node starting at root p with the given hash and key. The kc
         * argument caches comparableClassFor(key) upon first use comparing
         * keys.
         */
        final TreeNode<K, V> find(int h, Object k, Class<?> kc)
        {
            TreeNode<K, V> p = this;
            do
            {
                int ph, dir;
                K pk;
                TreeNode<K, V> pl = p.left, pr = p.right, q;
                if ((ph = p.hash) > h)
                    p = pl;
                else if (ph < h)
                    p = pr;
                else if ((pk = p.key) == k || (k != null && k.equals(pk)))
                    return p;
                else if (pl == null)
                    p = pr;
                else if (pr == null)
                    p = pl;
                else if ((kc != null || (kc = comparableClassFor(k)) != null)
                        && (dir = compareComparables(kc, k, pk)) != 0)
                    p = (dir < 0) ? pl : pr;
                else if ((q = pr.find(h, k, kc)) != null)
                    return q;
                else
                    p = pl;
            } while (p != null);
            return null;
        }

        /**
         * Calls find for root node.
         */
        final TreeNode<K, V> getTreeNode(int h, Object k)
        {
            return ((parent != null) ? root() : this).find(h, k, null);
        }

        /**
         * Tie-breaking utility for ordering insertions when equal hashCodes and
         * non-comparable. We don't require a total order, just a consistent
         * insertion rule to maintain equivalence across rebalancings.
         * Tie-breaking further than necessary simplifies testing a bit.
         */
        static int tieBreakOrder(Object a, Object b)
        {
            int d;
            if (a == null || b == null || (d = a.getClass().getName().compareTo(b.getClass().getName())) == 0)
                d = (System.identityHashCode(a) <= System.identityHashCode(b) ? -1 : 1);
            return d;
        }

        /**
         * Forms tree of the nodes linked from this node.
         */
        final void treeify(Node<K, V>[] tab)
        {
            TreeNode<K, V> root = null;
            for (TreeNode<K, V> x = this, next; x != null; x = next)
            {
                next = (TreeNode<K, V>)x.next;
                x.left = x.right = null;
                if (root == null)
                {
                    x.parent = null;
                    x.red = false;
                    root = x;
                }
                else
                {
                    K k = x.key;
                    int h = x.hash;
                    Class<?> kc = null;
                    for (TreeNode<K, V> p = root;;)
                    {
                        int dir, ph;
                        K pk = p.key;
                        if ((ph = p.hash) > h)
                            dir = -1;
                        else if (ph < h)
                            dir = 1;
                        else if ((kc == null && (kc = comparableClassFor(k)) == null)
                                || (dir = compareComparables(kc, k, pk)) == 0)
                            dir = tieBreakOrder(k, pk);

                        TreeNode<K, V> xp = p;
                        if ((p = (dir <= 0) ? p.left : p.right) == null)
                        {
                            x.parent = xp;
                            if (dir <= 0)
                                xp.left = x;
                            else
                                xp.right = x;
                            root = balanceInsertion(root, x);
                            break;
                        }
                    }
                }
            }
            moveRootToFront(tab, root);
        }

        /**
         * Returns a list of non-TreeNodes replacing those linked from this
         * node.
         */
        final Node<K, V> untreeify(HashMap<K, V> map)
        {
            Node<K, V> hd = null, tl = null;
            for (Node<K, V> q = this; q != null; q = q.next)
            {
                Node<K, V> p = map.replacementNode(q, null);
                if (tl == null)
                    hd = p;
                else
                    tl.next = p;
                tl = p;
            }
            return hd;
        }

        /**
         * Tree version of putVal.
         */
        final TreeNode<K, V> putTreeVal(HashMap<K, V> map, Node<K, V>[] tab, int h, K k, V v)
        {
            Class<?> kc = null;
            boolean searched = false;
            TreeNode<K, V> root = (parent != null) ? root() : this;
            for (TreeNode<K, V> p = root;;)
            {
                int dir, ph;
                K pk;
                if ((ph = p.hash) > h)
                    dir = -1;
                else if (ph < h)
                    dir = 1;
                else if ((pk = p.key) == k || (k != null && k.equals(pk)))
                    return p;
                else if ((kc == null && (kc = comparableClassFor(k)) == null)
                        || (dir = compareComparables(kc, k, pk)) == 0)
                {
                    if (!searched)
                    {
                        TreeNode<K, V> q, ch;
                        searched = true;
                        if (((ch = p.left) != null && (q = ch.find(h, k, kc)) != null)
                                || ((ch = p.right) != null && (q = ch.find(h, k, kc)) != null))
                            return q;
                    }
                    dir = tieBreakOrder(k, pk);
                }

                TreeNode<K, V> xp = p;
                if ((p = (dir <= 0) ? p.left : p.right) == null)
                {
                    Node<K, V> xpn = xp.next;
                    TreeNode<K, V> x = map.newTreeNode(h, k, v, xpn);
                    if (dir <= 0)
                        xp.left = x;
                    else
                        xp.right = x;
                    xp.next = x;
                    x.parent = x.prev = xp;
                    if (xpn != null)
                        ((TreeNode<K, V>)xpn).prev = x;
                    moveRootToFront(tab, balanceInsertion(root, x));
                    return null;
                }
            }
        }

        /**
         * Removes the given node, that must be present before this call. This
         * is messier than typical red-black deletion code because we cannot
         * swap the contents of an interior node with a leaf successor that is
         * pinned by "next" pointers that are accessible independently during
         * traversal. So instead we swap the tree linkages. If the current tree
         * appears to have too few nodes, the bin is converted back to a plain
         * bin. (The test triggers somewhere between 2 and 6 nodes, depending on
         * tree structure).
         */
        final void removeTreeNode(HashMap<K, V> map, Node<K, V>[] tab, boolean movable)
        {
            int n;
            if (tab == null || (n = tab.length) == 0)
                return;
            int index = (n - 1) & hash;
            TreeNode<K, V> first = (TreeNode<K, V>)tab[index], root = first, rl;
            TreeNode<K, V> succ = (TreeNode<K, V>)next, pred = prev;
            if (pred == null)
                tab[index] = first = succ;
            else
                pred.next = succ;
            if (succ != null)
                succ.prev = pred;
            if (first == null)
                return;
            if (root.parent != null)
                root = root.root();
            if (root == null || (movable && (root.right == null || (rl = root.left) == null || rl.left == null)))
            {
                tab[index] = first.untreeify(map); // too small
                return;
            }
            TreeNode<K, V> p = this, pl = left, pr = right, replacement;
            if (pl != null && pr != null)
            {
                TreeNode<K, V> s = pr, sl;
                while ((sl = s.left) != null) // find successor
                    s = sl;
                boolean c = s.red;
                s.red = p.red;
                p.red = c; // swap colors
                TreeNode<K, V> sr = s.right;
                TreeNode<K, V> pp = p.parent;
                if (s == pr)
                { // p was s's direct parent
                    p.parent = s;
                    s.right = p;
                }
                else
                {
                    TreeNode<K, V> sp = s.parent;
                    if ((p.parent = sp) != null)
                    {
                        if (s == sp.left)
                            sp.left = p;
                        else
                            sp.right = p;
                    }
                    if ((s.right = pr) != null)
                        pr.parent = s;
                }
                p.left = null;
                if ((p.right = sr) != null)
                    sr.parent = p;
                if ((s.left = pl) != null)
                    pl.parent = s;
                if ((s.parent = pp) == null)
                    root = s;
                else if (p == pp.left)
                    pp.left = s;
                else
                    pp.right = s;
                if (sr != null)
                    replacement = sr;
                else
                    replacement = p;
            }
            else if (pl != null)
                replacement = pl;
            else if (pr != null)
                replacement = pr;
            else
                replacement = p;
            if (replacement != p)
            {
                TreeNode<K, V> pp = replacement.parent = p.parent;
                if (pp == null)
                    root = replacement;
                else if (p == pp.left)
                    pp.left = replacement;
                else
                    pp.right = replacement;
                p.left = p.right = p.parent = null;
            }

            TreeNode<K, V> r = p.red ? root : balanceDeletion(root, replacement);

            if (replacement == p)
            { // detach
                TreeNode<K, V> pp = p.parent;
                p.parent = null;
                if (pp != null)
                {
                    if (p == pp.left)
                        pp.left = null;
                    else if (p == pp.right)
                        pp.right = null;
                }
            }
            if (movable)
                moveRootToFront(tab, r);
        }

        /**
         * 将一个树状容器中的节点分成上下两个树状容器，如果现在太小，则取消树状容器。仅从resize调用;参见上面关于分割位和索引的讨论。
         */
        final void split(HashMap<K, V> map, Node<K, V>[] tab, int index, int bit)
        {
            TreeNode<K, V> b = this;
            // Relink into lo and hi lists, preserving order
            TreeNode<K, V> loHead = null, loTail = null;
            TreeNode<K, V> hiHead = null, hiTail = null;
            int lc = 0, hc = 0;
            for (TreeNode<K, V> e = b, next; e != null; e = next)
            {
                next = (TreeNode<K, V>)e.next;
                e.next = null;
                if ((e.hash & bit) == 0)
                {
                    if ((e.prev = loTail) == null)
                        loHead = e;
                    else
                        loTail.next = e;
                    loTail = e;
                    ++lc;
                }
                else
                {
                    if ((e.prev = hiTail) == null)
                        hiHead = e;
                    else
                        hiTail.next = e;
                    hiTail = e;
                    ++hc;
                }
            }

            if (loHead != null)
            {
                if (lc <= UNTREEIFY_THRESHOLD)
                    tab[index] = loHead.untreeify(map);
                else
                {
                    tab[index] = loHead;
                    if (hiHead != null) // (else is already treeified)
                        loHead.treeify(tab);
                }
            }
            if (hiHead != null)
            {
                if (hc <= UNTREEIFY_THRESHOLD)
                    tab[index + bit] = hiHead.untreeify(map);
                else
                {
                    tab[index + bit] = hiHead;
                    if (loHead != null)
                        hiHead.treeify(tab);
                }
            }
        }

        /* ------------------------------------------------------------ */
        // Red-black tree methods, all adapted from CLR

        static <K, V> TreeNode<K, V> rotateLeft(TreeNode<K, V> root, TreeNode<K, V> p)
        {
            TreeNode<K, V> r, pp, rl;
            if (p != null && (r = p.right) != null)
            {
                if ((rl = p.right = r.left) != null)
                    rl.parent = p;
                if ((pp = r.parent = p.parent) == null)
                    (root = r).red = false;
                else if (pp.left == p)
                    pp.left = r;
                else
                    pp.right = r;
                r.left = p;
                p.parent = r;
            }
            return root;
        }

        static <K, V> TreeNode<K, V> rotateRight(TreeNode<K, V> root, TreeNode<K, V> p)
        {
            TreeNode<K, V> l, pp, lr;
            if (p != null && (l = p.left) != null)
            {
                if ((lr = p.left = l.right) != null)
                    lr.parent = p;
                if ((pp = l.parent = p.parent) == null)
                    (root = l).red = false;
                else if (pp.right == p)
                    pp.right = l;
                else
                    pp.left = l;
                l.right = p;
                p.parent = l;
            }
            return root;
        }

        static <K, V> TreeNode<K, V> balanceInsertion(TreeNode<K, V> root, TreeNode<K, V> x)
        {
            x.red = true;
            for (TreeNode<K, V> xp, xpp, xppl, xppr;;)
            {
                if ((xp = x.parent) == null)
                {
                    x.red = false;
                    return x;
                }
                else if (!xp.red || (xpp = xp.parent) == null)
                    return root;
                if (xp == (xppl = xpp.left))
                {
                    if ((xppr = xpp.right) != null && xppr.red)
                    {
                        xppr.red = false;
                        xp.red = false;
                        xpp.red = true;
                        x = xpp;
                    }
                    else
                    {
                        if (x == xp.right)
                        {
                            root = rotateLeft(root, x = xp);
                            xpp = (xp = x.parent) == null ? null : xp.parent;
                        }
                        if (xp != null)
                        {
                            xp.red = false;
                            if (xpp != null)
                            {
                                xpp.red = true;
                                root = rotateRight(root, xpp);
                            }
                        }
                    }
                }
                else
                {
                    if (xppl != null && xppl.red)
                    {
                        xppl.red = false;
                        xp.red = false;
                        xpp.red = true;
                        x = xpp;
                    }
                    else
                    {
                        if (x == xp.left)
                        {
                            root = rotateRight(root, x = xp);
                            xpp = (xp = x.parent) == null ? null : xp.parent;
                        }
                        if (xp != null)
                        {
                            xp.red = false;
                            if (xpp != null)
                            {
                                xpp.red = true;
                                root = rotateLeft(root, xpp);
                            }
                        }
                    }
                }
            }
        }

        static <K, V> TreeNode<K, V> balanceDeletion(TreeNode<K, V> root, TreeNode<K, V> x)
        {
            for (TreeNode<K, V> xp, xpl, xpr;;)
            {
                if (x == null || x == root)
                    return root;
                else if ((xp = x.parent) == null)
                {
                    x.red = false;
                    return x;
                }
                else if (x.red)
                {
                    x.red = false;
                    return root;
                }
                else if ((xpl = xp.left) == x)
                {
                    if ((xpr = xp.right) != null && xpr.red)
                    {
                        xpr.red = false;
                        xp.red = true;
                        root = rotateLeft(root, xp);
                        xpr = (xp = x.parent) == null ? null : xp.right;
                    }
                    if (xpr == null)
                        x = xp;
                    else
                    {
                        TreeNode<K, V> sl = xpr.left, sr = xpr.right;
                        if ((sr == null || !sr.red) && (sl == null || !sl.red))
                        {
                            xpr.red = true;
                            x = xp;
                        }
                        else
                        {
                            if (sr == null || !sr.red)
                            {
                                if (sl != null)
                                    sl.red = false;
                                xpr.red = true;
                                root = rotateRight(root, xpr);
                                xpr = (xp = x.parent) == null ? null : xp.right;
                            }
                            if (xpr != null)
                            {
                                xpr.red = (xp == null) ? false : xp.red;
                                if ((sr = xpr.right) != null)
                                    sr.red = false;
                            }
                            if (xp != null)
                            {
                                xp.red = false;
                                root = rotateLeft(root, xp);
                            }
                            x = root;
                        }
                    }
                }
                else
                { // symmetric
                    if (xpl != null && xpl.red)
                    {
                        xpl.red = false;
                        xp.red = true;
                        root = rotateRight(root, xp);
                        xpl = (xp = x.parent) == null ? null : xp.left;
                    }
                    if (xpl == null)
                        x = xp;
                    else
                    {
                        TreeNode<K, V> sl = xpl.left, sr = xpl.right;
                        if ((sl == null || !sl.red) && (sr == null || !sr.red))
                        {
                            xpl.red = true;
                            x = xp;
                        }
                        else
                        {
                            if (sl == null || !sl.red)
                            {
                                if (sr != null)
                                    sr.red = false;
                                xpl.red = true;
                                root = rotateLeft(root, xpl);
                                xpl = (xp = x.parent) == null ? null : xp.left;
                            }
                            if (xpl != null)
                            {
                                xpl.red = (xp == null) ? false : xp.red;
                                if ((sl = xpl.left) != null)
                                    sl.red = false;
                            }
                            if (xp != null)
                            {
                                xp.red = false;
                                root = rotateRight(root, xp);
                            }
                            x = root;
                        }
                    }
                }
            }
        }

        /**
         * Recursive invariant check
         */
        static <K, V> boolean checkInvariants(TreeNode<K, V> t)
        {
            TreeNode<K, V> tp = t.parent, tl = t.left, tr = t.right, tb = t.prev, tn = (TreeNode<K, V>)t.next;
            if (tb != null && tb.next != t)
                return false;
            if (tn != null && tn.prev != t)
                return false;
            if (tp != null && t != tp.left && t != tp.right)
                return false;
            if (tl != null && (tl.parent != t || tl.hash > t.hash))
                return false;
            if (tr != null && (tr.parent != t || tr.hash < t.hash))
                return false;
            if (t.red && tl != null && tl.red && tr != null && tr.red)
                return false;
            if (tl != null && !checkInvariants(tl))
                return false;
            if (tr != null && !checkInvariants(tr))
                return false;
            return true;
        }
    }

}