HashMap解读_哈希map

1.简介

HashMap ，是一种散列表，用于存储 key-value 键值对的数据结构，一般翻译为“哈希表”，提供平均时间复杂度为 O(1) 的、基于 key 级别的 get/put 等操作。

2.哈希表结构

哈希表结构为数组，链表和红黑树。如图

哈希表渴望实现O1的查找时间复杂度，因此采用数组作为基础结构，通过哈希函数，计算key的哈希值，哈希表指示存储数组的下标，但是会出现不同key对应同一个哈希值，则称作哈希碰撞，采取拉链法解决，将同一下标的所有节点链接为链表。但是当链表长度过长，hash表便也失去了平均o1的特性。因此在一定条件下，链表将树化为红黑树,jdk1.7之前只有拉链，1.8加入红黑树特性。

3.什么是Hash

Hash也称散列、哈希，对应的英文都是Hash。基本原理就是把任意长度的输入，通过Hash算法变成固定长度的输出。这个映射的规则就是对应的Hash算法，而原始数据映射后的二进制串就是哈希值。

• 1.从Hash值不可以反向推导出原始数据
• 2.输入数据的微小变化会得到完全不同的Hash值相同的数据一定可以得到相同的值
• 3.哈希算法的执行效率要高效，长的文本也能快速计算Hash值
• 4.Hash算法的冲突概率要小

由于Hash原理就是将输入空间映射成Hash空间，而Hash空间远远小于输入空间，根据抽屉原理，一定存在不同输出有相同的映射

抽屉原理: 桌子上有10个苹果，将其放在9个抽屉里面，那必有一个抽屉不少于2个苹果

4.HashMap源码理解

HashMap结构

内部类

• 1)Node：存储基本的哈希值和键值对
  Node结构

   static class Node<K,V> implements Map.Entry<K,V> {
      final int hash;
      final K key;
      V value;
      Node<K,V> next;
   ....
   }
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• 2)KeySet：所有Key的哈希集合

  ​ 与node数组共享key,对key的操作是互相影响的。并且只支持删除操作

• 3)Values: ：所有value的哈希集合，同理keySet

• 4)EntrySet：所有node的哈希集合，同理keySet

• 5)HashIterator: 迭代器，遍历node使用

• 6)KeyIterator： 迭代器实现

• 7)EntryIterator： 迭代器实现

• 8)ValueIterator: 迭代器实现

• 9)HashMapSpiterator ：切割node数组，供并行使用

• 10)KeySpiterator：切割器实现

• 11)ValueSpiterator：切割器实现

• 12)EntrySpiterator： 切割器实现

• 13)TreeNode：红黑树node节点

成员变量

	//默认初始化容量为16
    static final int DEFAULT_INITIAL_CAPACITY = 1 << 4;
   	//最大的数组容量为2的30次方
    static final int MAXIMUM_CAPACITY = 1 << 30;
   	//默认负载系数
    static final float DEFAULT_LOAD_FACTOR = 0.75f;
    //链表长度树化为红黑树的阈值
    static final int TREEIFY_THRESHOLD = 8;
    //红黑树退化为链表的阈值
    static final int UNTREEIFY_THRESHOLD = 6;
   //最小树化的节点数量阈值
    static final int MIN_TREEIFY_CAPACITY = 64;
 	//存放节点的数组，懒加载创建
    transient  Node<K,V>[] table;
    //key_value哈希集合，懒加载创建
    transient Set<Map.Entry<K,V>> entrySet;
    //数组实际节点数量
    transient int size;
   //node节点的增加删除次数，不包括更新
    transient int modCount;
    //下次进行扩容的阈值 容量*负载因子
    int threshold;
    //负载因子
    final float loadFactor;
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成员方法，挑体现核心思想的方法

• 初始化

  

• 查找node

  

• 插入/更新

  

• 删除

  

下面是我阅读源码添加的注释,注释待补充完整

package my;

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.*;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Function;

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

    private static final long serialVersionUID = 362498820763181265L;
    //默认初始化容量为16
    static final int DEFAULT_INITIAL_CAPACITY = 1 << 4;

   //最大的数组容量为2的30次方
    static final int MAXIMUM_CAPACITY = 1 << 30;

   //默认负载系数
    static final float DEFAULT_LOAD_FACTOR = 0.75f;

    //链表长度树化为红黑树的阈值
    static final int TREEIFY_THRESHOLD = 8;

    //红黑树退化为链表的阈值
    static final int UNTREEIFY_THRESHOLD = 6;

   //最小树化的节点数量阈值
    static final int MIN_TREEIFY_CAPACITY = 64;

    //基础节点 存放key,value,hash,下一个node指针
    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;
        }
    }

    //静态方法

   //计算key的哈希值
    /*
    how: key的hash值的前16位异或后16位
    why: 通过混合哈希码的高位和低位，使得hash值更加分散，这种做法称作扰动
    */
    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));
    }

    //do: 获取一个恰好大于输入值的2的次方数，在小于最大数组容量下
    static final int tableSizeFor(int cap) {
        int n = cap - 1;
        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;
    }

    /* ---------------- 成员 -------------- */

    //存放节点的数组，懒加载创建
    transient  Node<K,V>[] table;

    //key_value哈希集合，懒加载创建
    transient Set<Map.Entry<K,V>> entrySet;

    //数组实际节点数量
    transient int size;

   //node节点的增加删除次数，不包括更新
    transient int modCount;

    //下次进行扩容的阈值 容量*负载因子
    int threshold;

    //负载因子
    final float loadFactor;

    /* ---------------- 对外操作 -------------- */

    //输出初始化容量，负载因子进行 初始化 容量，负载因子
    public HashMap(int initialCapacity, float loadFactor) {
        if (initialCapacity < 0)//容量非法
            throw new IllegalArgumentException("Illegal initial capacity: " +
                    initialCapacity);
        if (initialCapacity > MAXIMUM_CAPACITY)//最大容量
            initialCapacity = MAXIMUM_CAPACITY;
        if (loadFactor <= 0 || Float.isNaN(loadFactor))//负载因子非法
            throw new IllegalArgumentException("Illegal load factor: " +
                    loadFactor);
        this.loadFactor = loadFactor;
        this.threshold = tableSizeFor(initialCapacity);//2的次方容量
    }

    //调用 HashMap(int initialCapacity, float loadFactor)
    public HashMap(int initialCapacity) {
        this(initialCapacity, DEFAULT_LOAD_FACTOR);
    }

   //初始化负载因子为0.75
    public HashMap() {
        this.loadFactor = DEFAULT_LOAD_FACTOR; // 所有其他的值都为默认
    }

   //创建特定的map
    public HashMap(Map<? extends K, ? extends V> m) {
        this.loadFactor = DEFAULT_LOAD_FACTOR;
        putMapEntries(m, false);
    }

    //实现Map.putAll和Map构造函数
    final void putMapEntries(Map<? extends K, ? extends V> m, boolean evict) {
        int s = m.size();
        if (s > 0) {
            if (table == null) { // pre-size
                float ft = ((float)s / loadFactor) + 1.0F;
                int t = ((ft < (float)MAXIMUM_CAPACITY) ?
                        (int)ft : MAXIMUM_CAPACITY);
                if (t > threshold)
                    threshold = tableSizeFor(t);
            }
            else if (s > threshold)
                resize();
            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);
            }
        }
    }

    //返回node节点数量
    public int size() {
        return size;
    }

   //node节点是否等于0
    public boolean isEmpty() {
        return size == 0;
    }

    //通过key获取value,如果不存在则返回为空，调用getNode(int hash, Object key)实现
    public V get(Object key) {
         Node<K,V> e;
        return (e = getNode(hash(key), key)) == null ? null : e.value;
    }

    //通过hash值找到数组下标，通过key找到node
    final  Node<K,V> getNode(int hash, Object key) {
        //变量解释
        //tab 被赋值为node数组
        //first 被赋值为下标处第一个节点
        //n 节点数量
        //k first.key
         Node<K,V>[] tab;  Node<K,V> first, e; int n; K k;
         //数组不为空 & 长度不为0 & 第一个节点不为空
        if ((tab = table) != null && (n = tab.length) > 0 &&
                (first = tab[(n - 1) & hash]) != null) {
            if (first.hash == hash &&
                    ((k = first.key) == key || (key != null && key.equals(k))))
                return first;//检查第一个节点是否为寻找值
            if ((e = first.next) != null) {
                if (first instanceof  TreeNode)
                    //红黑树寻找
                    return (( TreeNode<K,V>)first).getTreeNode(hash, key);
                //链表寻找
                do {
                    if (e.hash == hash &&
                            ((k = e.key) == key || (key != null && key.equals(k))))
                        return e;
                } while ((e = e.next) != null);
            }
        }
        //找不到
        return null;
    }

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

   //插入键值对。如果是替换则返回上一个value值，否则返回为null
    public V put(K key, V value) {
        return putVal(hash(key), key, value, false, true);
    }

    /**
     * 插入键值对
     * @param onlyIfAbsent 如果为true，则不更改现有值
     * @param evict 如果为false，则表处于创建模式。
     * 如果是替换则返回上一个value值，否则返回为null
     */
    final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                   boolean evict) {
        //变量解释
        //tab 被赋值为node数组
        //first 被赋值为下标处第一个节点
        //n 节点数量
        //i 下标
         Node<K,V>[] tab;  Node<K,V> p; int n, i;

        if ((tab = table) == null || (n = tab.length) == 0)
            //懒加载创建node数组
            n = (tab = resize()).length;
        if ((p = tab[i = (n - 1) & hash]) == null)
            //如果下标处没有节点，直接插入即可
            tab[i] = newNode(hash, key, value, null);
        else {
            //变量解释
            //e 被替换的节点
            //k 当前节点的key
             Node<K,V> e; K k;
            if (p.hash == hash &&
                    ((k = p.key) == key || (key != null && key.equals(k))))
                e = p;
            else if (p instanceof  TreeNode)
                //红黑树替换
                e = (( TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
            else {
                //链表替换
                for (int binCount = 0; ; ++binCount) {
                    if ((e = p.next) == null) {
                        p.next = newNode(hash, key, value, null);
                        if (binCount >= TREEIFY_THRESHOLD - 1) //节点数量是否达到树化阈值
                            treeifyBin(tab, hash);
                        break;
                    }
                    if (e.hash == hash &&
                            ((k = e.key) == key || (key != null && key.equals(k))))
                        break;
                    p = e;
                }
            }
            //更新
            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)//达到扩容阈值
            resize();
        afterNodeInsertion(evict);//插入后的操作，空实现
        return null;//非覆盖的返回值
    }

    //初始化节点数组或者扩容数组使得新数组容量的两倍（容量，阈值）
    final  Node<K,V>[] resize() {
        //变量解释
        //oldTab 被赋值为node原数组
        //oldCap 被赋值为原容量
        //oldThr  原扩容阈值
        //newCap 新容量 newThr 新扩容阈值
         Node<K,V>[] oldTab = table;
        int oldCap = (oldTab == null) ? 0 : oldTab.length;
        int oldThr = threshold;
        int newCap, newThr = 0;
        if (oldCap > 0) {
            //非空数组
            if (oldCap >= MAXIMUM_CAPACITY) {
                //如果容量已经最大，那么设置阈值为int的最大值后不再处理
                threshold = Integer.MAX_VALUE;
                return oldTab;
            }
            else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
                    oldCap >= DEFAULT_INITIAL_CAPACITY)
                //容量增大为原来的两倍，如果原来的容量已经大于默认容量（16），那么扩容阈值也增大原来的两倍
                newThr = oldThr << 1;
        }
        //空数组
        else if (oldThr > 0) //容量变为原来的扩容阈值
            newCap = oldThr;
        else {
            //阈值为0表示使用默认值
            newCap = DEFAULT_INITIAL_CAPACITY;
            newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
        }
        //对应352
        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) {
            //遍历每一个桶
            for (int j = 0; j < oldCap; ++j) {
                 Node<K,V> e;
                if ((e = oldTab[j]) != null) {
                    oldTab[j] = null;//GC
                    if (e.next == null)
                        //一个节点直接计算hash值域插入
                        newTab[e.hash & (newCap - 1)] = e;
                    else if (e instanceof  TreeNode)
                        //红黑树扩容
                        (( TreeNode<K,V>)e).split(this, newTab, j, oldCap);
                    else { // preserve order
                        //链表扩容
                        //由于hash计算机制，同一下标的节点在新节点hash计算得到结果的下标 只可能保持或者移动向右移动扩大原容量位移
                         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;
    }

   //hash对应桶树化
    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);
        }
    }

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

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

    /**
     * @param value matchValue为true有效
     * @param matchValue 是否需要匹配value
     * @param movable 如果为false，则删除时不移动其他节点
     */
    //删除节点,并且返回
    final  Node<K,V> removeNode(int hash, Object key, Object value,
                                                 boolean matchValue, boolean movable) {
        //变量解释
        //tab node数组
        //p 下标处第一个节点
        //n node数组长度
        //index 下标
         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))))
                //检查第一个节点
                node = p;
            else if ((e = p.next) != null) {
                if (p instanceof  TreeNode)
                    //红黑树删除
                    node = (( TreeNode<K,V>)p).getTreeNode(hash, key);
                else {
                    //链表删除
                    do {
                        if (e.hash == hash &&
                                ((k = e.key) == key ||
                                        (key != null && key.equals(k)))) {
                            node = e;
                            break;
                        }
                        p = e;
                    } while ((e = e.next) != null);
                }
            }
            //如果节点存在，则执行删除
            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;
    }


     //清空所有节点
    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;
        }
    }

    //检查map中是否有value
    //没看到红黑树的遍历为啥？
    public boolean containsValue(Object value) {
         Node<K,V>[] tab; V v;
        if ((tab = table) != null && size > 0) {
            for (int i = 0; i < tab.length; ++i) {
                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;
    }


    //返回所有key
    public Set<K> keySet() {
        Set<K> ks = keySet;
        if (ks == null) {
            ks = new  KeySet();
            keySet = ks;
        }
        return ks;
    }
    //可以对key进行删除，不支持增加。map集合进行增加删除node时，迭代操作将不可执行，显示为未定义
    final class KeySet extends AbstractSet<K> {
        public final int size()                 { return size; }
        //todo 为什么这个clear这样做
        public final void clear()               {  this.clear(); }
        //返回key的迭代器
        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;
        }
        //todo Spliterator
        public final Spliterator<K> spliterator() {
            return new  KeySpliterator<>( this, 0, -1, 0, 0);
        }
        //迭代遍历
        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);
                }
                //检测map是否修改了map的keyset集合
                if (modCount != mc)
                    throw new ConcurrentModificationException();
            }
        }
    }

   //返回所有value集合
    public Collection<V> values() {
        Collection<V> vs = values;
        if (vs == null) {
            vs = new  Values();
            values = vs;
        }
        return vs;
    }
    //如果有任意节点的value值在迭代时进行修改，那么迭代将失败
    final class Values extends AbstractCollection<V> {
        public final int size()                 { return size; }
        public final void clear()               {  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<>( 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();
            }
        }
    }

    //返回所有node的set集合，懒加载
    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()               {  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<>( 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();
            }
        }
    }

    // jdk8重写方法

    //获取某个key的值，无则返回默认值
    @Override
    public V getOrDefault(Object key, V defaultValue) {
         Node<K,V> e;
        return (e = getNode(hash(key), key)) == null ? defaultValue : e.value;
    }

    //插入值，需要key值不存在，也就是不进行覆盖操作
    @Override
    public V putIfAbsent(K key, V value) {
        return putVal(hash(key), key, value, true, true);
    }
    //删除节点，key-value都匹配
    @Override
    public boolean remove(Object key, Object value) {
        return removeNode(hash(key), key, value, true, true) != null;
    }
    //覆盖key-value都匹配
    @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;
            //空实现
            afterNodeAccess(e);
            return true;
        }
        return false;
    }

    //覆盖匹配key
    @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;
            //空实现
            afterNodeAccess(e);
            return oldValue;
        }
        return null;
    }

    //如果 key 对应的 value 不存在，则使用获取 mappingFunction 重新计算后的值，并保存为该 key 的 value，否则返回 value。
    @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) {
            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;
            if (old != null && (oldValue = old.value) != null) {
                afterNodeAccess(old);
                return oldValue;
            }
        }
        V v = mappingFunction.apply(key);
        if (v == null) {
            return null;
        } else if (old != null) {
            old.value = v;
            afterNodeAccess(old);
            return v;
        }
        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;
    }
    //如果 key 对应的 value 不存在，则返回该 null，如果存在，则返回通过 remappingFunction 重新计算后的值。
    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;
            }
            else
                removeNode(hash, key, null, false, true);
        }
        return null;
    }

    //对 hashMap 中指定 key 的值进行重新计算。
    @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;
    }
    //先判断指定的 key 是否存在，如果不存在，则添加键值对到 hashMap 中。
    //如果 key 对应的 value 不存在，则返回该 value 值，如果存在，则返回通过 remappingFunction 重新计算后的值。
    @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;
    }

    //迭代
    @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();
        }
    }

    //全部替换，使用传入的函数
    @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();
        }
    }

    /* ----------------------克隆和序列化---------------------------- */


   //浅克隆，键值对没有被可能，todo 仍然共享数据
    @SuppressWarnings("unchecked")
    @Override
    public Object clone() {
        java.util.HashMap<K,V> result;
        try {
            result = (java.util.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;
    }

    //序列化HashSet时也使用这些方法
    final float loadFactor() { return loadFactor; }
    final int capacity() {
        return (table != null) ? table.length :
                (threshold > 0) ? threshold :
                        DEFAULT_INITIAL_CAPACITY;
    }

    //将HashMap实例的状态保存到流中（即序列化）。无顺序
    private void writeObject(java.io.ObjectOutputStream s)
            throws IOException {
        int buckets = capacity();
        //阈值，负载因子和任何内容
        s.defaultWriteObject();
        s.writeInt(buckets);
        s.writeInt(size);
        internalWriteEntries(s);
    }

    //从流中重新构造HashMap实例（即反序列化）。
    private void readObject(java.io.ObjectInputStream s)
            throws IOException, ClassNotFoundException {
        //阈值，负载因子和任何内容
        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);
            @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);
            }
        }
    }

    /* ------------------------迭代器------------------------- */

    abstract class HashIterator {
         Node<K,V> next;        // 下一个实体
         Node<K,V> current;     // 现在的实体
        int expectedModCount;  // 用于快速失败
        int index;             // 当前下标

        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(); }
    }

    /* ---------------------切割卡槽，并行使用----------------------------- */
    // 切割器

    static class HashMapSpliterator<K,V> {
        final java.util.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(java.util.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) {
                java.util.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(java.util.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();
            java.util.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(java.util.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();
            java.util.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(java.util.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();
            java.util.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支持-------------------------- */


    /*
     *  以下方法旨在
        被LinkedHashMap覆盖，但不被任何其他子类覆盖。
        几乎所有其他内部方法都受到包保护
        但声明为final，因此可以由LinkedHashMap、view classes和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);
                }
            }
        }
    }

    /* -------------------------红黑树--------------------------- */

    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);
        }

        //返回包含调用节点的树的根。
        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.
         * @return root of tree
         */
        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(java.util.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(java.util.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(java.util.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 || 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);
        }

        /**
         * Splits nodes in a tree bin into lower and upper tree bins,
         * or untreeifies if now too small. Called only from resize;
         * see above discussion about split bits and indices.
         *
         * @param map the map
         * @param tab the table for recording bin heads
         * @param index the index of the table being split
         * @param bit the bit of hash to split on
         */
        final void split(java.util.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;
        }
    }

}

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参考资料

https://www.bilibili.com/video/BV1LJ411W7dP/?p=8&spm_id_from=333.1007.top_right_bar_window_history.content.click&vd_source=f6a308f875296edd5f437b68e0c3253a

https://www.runoob.com/java/java-hashmap.html