JDK 1.8 HashMap源码分析（部分）

小鱼儿 2022-05-20 03:11 86阅读 0赞

public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable { 
    
        private static final long serialVersionUID = 362498820763181265L
    
        /** * hashmap初始容量，必须为2的n次 * 注：根据数据量设置合适的初始值，可以避免hashmap因扩容带来的开销 */
        static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16
    
        /** * hashmap最大容量，必须为2的次方，且不能大于1<<30 * 注：若初始值比1<<30大，则设置初始值为1<<30 */
        static final int MAXIMUM_CAPACITY = 1 << 30;
    
        /** * 负载因子. * 注：数据量超过hashmap容量乘以负载因子的结果，hashmap扩容为原来容量的一倍 */
        static final float DEFAULT_LOAD_FACTOR = 0.75f;
    
        /** * hashmap中链表树形化阈值，链表大于此值会转换成红黑树（jdk1.8hashmap引入红黑树） * 注：（1）jdk1.8以前hashmap结构为数组+链表，jdk1.8hashmap结构为数组+链表+红黑树 * （2）hashmap容量超过MIN_TREEIFY_CAPACITY值链表才会树形化，否则只会扩容 * （3）极端情况，hashmap元素全部集中在一个链表，查找时间复杂度为O(n)，替换成红黑树后为O(logn) */
        static final int TREEIFY_THRESHOLD = 8;
    
        /** * hashmap扩容后，红黑树数据小于或等于此值可将红黑树还原成链表 */
        static final int UNTREEIFY_THRESHOLD = 6;
    
        /** * hashmap容量超过MIN_TREEIFY_CAPACITY值链表才会树形化，否则只会扩容 * 注：为了平衡扩容和树形化，此值不小于4*TREEIFY_THRESHOLD */
        static final int MIN_TREEIFY_CAPACITY = 64;
    
        /** * Node<K,V> 类用来实现数组及链表的数据结构 */
        static class Node<K,V> implements Map.Entry<K,V> {
            final int hash;  //指key对应的hash值
            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 -------------- */
    
        /** * key的hash值的计算方法。key的hash值高16位不变，低16位与高16位异或作为key的最终hash值（h >>> 16，表示无符号右移16位，高位补0，任何数跟0异或都是其本身，因此key的hash值高16位不变。） */
        static final int hash(Object key) {
            int h;
            return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
        }
    
    
        /** * 用于找到大于等于initialCapacity的最小的2的幂 */
        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;
        }
    
    
        /** * hashmap数据结构，数组+链表 */
        transient Node<K,V>[] table;
    
        /** * Holds cached entrySet(). Note that AbstractMap fields are used * for keySet() and values(). */
        transient Set<Map.Entry<K,V>> entrySet;
    
        /** * hashmap中数据量 */
        transient int size;
    
        /** * hashmap内容修改都将反应在modCount上，线程不安全访问时，会抛出异常（本地保存的修改次数与modCount不同，表示其他线程修改过modCount，该变量使用volatile修饰，保证线程间的可见性） */
        transient int modCount;
    
        /** * threshold表示当HashMap的size大于threshold时会执行resize操作，threshold=capacity*loadFactor */
        int threshold;
    
        /** * 加载因子，用来衡量HashMap满的程度。loadFactor的默认值为0.75f。计算HashMap的实时装载因子的方法为：size/capacity */
        final float loadFactor;
    
        /** * 构造一个空的hashmap，指定初始容量和加载因子 */
        public HashMap(int initialCapacity, float loadFactor) {
            // 初始容量小于0抛出IllegalArgumentException异常
            if (initialCapacity < 0)
                throw new IllegalArgumentException("Illegal initial capacity: " +
                                                   initialCapacity);
            // 初始容量大于MAXIMUM_CAPACITY（1<<30），将初始容量置为MAXIMUM_CAPACITY
            if (initialCapacity > MAXIMUM_CAPACITY)
                initialCapacity = MAXIMUM_CAPACITY;
            // 加载因子小于等于0或者loadFactor为NaN，抛出IllegalArgumentException异常
            if (loadFactor <= 0 || Float.isNaN(loadFactor))
                throw new IllegalArgumentException("Illegal load factor: " +
                                                   loadFactor);
            this.loadFactor = loadFactor;
            // 注意，得到的这个capacity却被赋值给了threshold。
            // this.threshold = tableSizeFor(initialCapacity);
            // 开始以为这个是个Bug，感觉应该这么写：
            // this.threshold = tableSizeFor(initialCapacity) * this.loadFactor;
            // 这样才符合threshold的意思（当HashMap的size到达threshold这个阈值时会扩容）。 
            // 但是，请注意，在构造方法中，并没有对table这个成员变量进行初始化，table的初始化被推迟到了put方法中，
            // 在put方法中会对threshold重新计算
            this.threshold = tableSizeFor(initialCapacity);
        }
    
        /** * 构造一个空的hashmap，指定初始容量，默认加载因子0.75f */
        public HashMap(int initialCapacity) {
            this(initialCapacity, DEFAULT_LOAD_FACTOR);
        }
    
        /** * 构造一个空的hashmap，默认容量16，默认加载因子0.75f */
        public HashMap() {
            this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
        }
    
        /** * 创建一个新的hashmap，将指定的m存入新的hashmap，默认加载因子为0.75f */
        public HashMap(Map<? extends K, ? extends V> m) {
            this.loadFactor = DEFAULT_LOAD_FACTOR;
            putMapEntries(m, false);
        }
    
        /** * 将指定的m的k-v值存入当前hashmap * evict：这个参数如果为true，那么每插入一个新值，就把链表头"踢出去"，保持链表元素数目不变（只有LinkedHashMap使用此参数） */
        final void putMapEntries(Map<? extends K, ? extends V> m, boolean evict) {
            int s = m.size();
            // 如果传入的m不是空的hashmap，则存入当前hashmap
            if (s > 0) {
                // 判断table是否已初始化，table 为当前hashmap中存储元素的数据结构（数组+链表）
                if (table == null) { // pre-size
                    // 为初始化，s为m的元素个数
                    float ft = ((float)s / loadFactor) + 1.0F;
                    int t = ((ft < (float)MAXIMUM_CAPACITY) ?
                             (int)ft : MAXIMUM_CAPACITY);
                    // 如果t大于阈值，重新计算threshold为大于t的2的幂
                    if (t > threshold)
                        threshold = tableSizeFor(t);
                }
                else if (s > threshold){
                    // 如果m的大小大于threshold阈值，进行扩容
                    resize();
                }
                // 使用entrySet遍历方式将m的元素添加到当前hashmap中
                for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {
                    K key = e.getKey();
                    V value = e.getValue();
                    // 调用当前hashmap方法添加元素
                    putVal(hash(key), key, value, false, evict);
                }
            }
        }
    
        /** * 获取当前hashmap元素个数 */
        public int size() {
            return size;
        }
    
        /** * 判断当前hashmap是否为空的hashmap */
        public boolean isEmpty() {
            return size == 0;
        }
    
        /** * 获取当前hashmap中key对应的value,具体的get算法查看方法getNode(int hash, Object key) * (1)如果key在hashmap中没有存储对应键值对，则返回null * (2)如果key=null,hashmap中最多存在一个key=null的键值对,返回key=null对应的value */
        public V get(Object key) {
            Node<K,V> e;
            return (e = getNode(hash(key), key)) == null ? null : e.value;
        }
    
        /** * 根据key的hash值和key在当前hashmap中遍历找到对应的存储节点（Node<K,V>类型的对象） */
        final Node<K,V> getNode(int hash, Object key) {
            // tab用于存储当前table数据结构
            // first用于存储table中第一个节点
            // e用于存储遍历时当前节点的下一个节点
            // n用于存储table数组的长度（不是元素个数，元素个数=数组长度+链表长度）
            // k用于存储当前比对节点的key值
            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) {
                // tab[(n - 1) & hash]定位key对应的节点在数组的第几个元素
                if (first.hash == hash && // always check first node
                    ((k = first.key) == key || (key != null && key.equals(k))))
                    // 满足条件即为找到：（1）当前节点的key的hash值和参数key的hash值相等（2）当前节点的key与参数key相同或字符串相等
                    return first;
                if ((e = first.next) != null) {
                    //第一个节点不是要找的节点，找first的下一个节点（前提是first存在下一个节点）
                    if (first instanceof TreeNode)
                        // 如果第一个节点是TreeNode类型（红黑树,说明该链表中数据量已经大于TREEIFY_THRESHOLD，
                        // 已经转换成红黑树）,则按照红黑树算法查找节点
                        return ((TreeNode<K,V>)first).getTreeNode(hash, key);
                    do {
                        // 循环遍历链表直到找到为止，未找到跳出循环执行最后return null;
                        if (e.hash == hash &&
                            ((k = e.key) == key || (key != null && key.equals(k))))
                            return e;
                    } while ((e = e.next) != null);
                }
                //first不存在下一个节点，而first又不是要找的，执行最后的return null，即未找到key对应的节点
            }
            return null;
        }
    
        /** * 当前hashmap是否包含key对应的节点 */
        public boolean containsKey(Object key) {
            // 通过getNode方法查询当前hashmap中key对应的节点，
            // 未找到（返回null）结果false（null!=null），找到（返回节点）结果为true(Node!=null)
            return getNode(hash(key), key) != null;
        }
    
        /** * 向当前hashmap存入key-value键值对，若已存在key对应的节点，则被新值替换，方法返回旧值 * * */
        public V put(K key, V value) {
            return putVal(hash(key), key, value, false, true);
        }
    
        /** * 当前hashmap存入或替换key-value * （1）hash：key的hash值 * （2）key：参数key * （3）value：需要存入或替换的值 * （4）onlyIfAbsent：源码中默认为false,表示不存在新增，存在则替换;若为true表示存在则不更新 * （5）evict：LinkedHashMap会用到，HashMap不使用 */
        final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                       boolean evict) {
            // tab用于存储当前hashmap的table数据结构
            // p用于存储当前定位到的节点
            // n用来表示当前hashmap的table的容量大小
            // i用来表示根据key的hash值定位到的table数组下标
            Node<K,V>[] tab; Node<K,V> p; int n, i;
            if ((tab = table) == null || (n = tab.length) == 0)
                // 当前hashmap的table为null或者大小为0,则扩容
                n = (tab = resize()).length;
            if ((p = tab[i = (n - 1) & hash]) == null)
                // tab[i]为null,则表示i下标中的链表没有数据,因此将key-value创建新的节点保存在tab[i]链表表头
                tab[i] = newNode(hash, key, value, null);
            else {
                //否则,表示tab[i]链表中存在元素
                Node<K,V> e; K k;
                if (p.hash == hash &&
                    ((k = p.key) == key || (key != null && key.equals(k))))
                    // tab[i]链表第一个元素的key就是要put进去的key,将第一个元素赋值给e变量
                    e = p;
                else if (p instanceof TreeNode)
                    // 若tab[i]链表第一个元素p为红黑树类型（链表长度超过TREEIFY_THRESHOLD，
                    // 进行过treeifyBin(tab, hash)），则按照红黑树算法进行put操作
                    e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
                else {
                    for (int binCount = 0; ; ++binCount) {
                        // binCount表示链表遍历计数,用于判断是否将链表转换为红黑树
                        if ((e = p.next) == null) {
                            // 遍历到链表表尾,则创建节点设置为p.next
                            p.next = newNode(hash, key, value, null);
                            if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                                treeifyBin(tab, hash);
                            break;
                        }
                        if (e.hash == hash &&
                            ((k = e.key) == key || (key != null && key.equals(k))))
                            break;
                        p = e;
                    }
                }
                if (e != null) { // existing mapping for key
                    // e!=null表示e节点为key对应要更新的节点，临时保存e节点的旧值oldValue
                    V oldValue = e.value;
                    if (!onlyIfAbsent || oldValue == null)
                        // 设置新的值
                        e.value = value;
                    afterNodeAccess(e);
                    // 返回key对应的旧值
                    return oldValue;
                }
            }
            // 当前hashmap修改计数加1,用于在线程不安全访问时,抛出异常,保证hashmap数据正确性
            ++modCount;
            if (++size > threshold)
                // 添加新元素后大小加1,若大小大于阈值,扩容
                resize();
            afterNodeInsertion(evict);
            // 添加的为新元素,因此旧值为null
            return null;
        }
    
        /** * 当前hashmap扩容，返回扩容以后的Node<K,V>[] */
        final Node<K,V>[] resize() {
            // 临时保存旧table
            Node<K,V>[] oldTab = table;
            // 临时保存旧table容量
            int oldCap = (oldTab == null) ? 0 : oldTab.length;
            // 临时保存旧hashmap的阈值
            int oldThr = threshold;
            // 初始化新容量=0,新阈值=0
            int newCap, newThr = 0;
            if (oldCap > 0) {
            //如果旧table有数据，即oldCap>0
                if (oldCap >= MAXIMUM_CAPACITY) {
                    // 旧table容量大于或等于1<<30,设置当前hashmap阈值为Integer的最大值并返回旧table(不能继续扩容,
                    // 但设置阈值后,还可以继续装数据)
                    threshold = Integer.MAX_VALUE;
                    return oldTab;
                }
                else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
                         oldCap >= DEFAULT_INITIAL_CAPACITY)
                    // 旧table容量小于最大容量限制并且大于或等于默认容量16,将容量扩大一倍,阈值扩大一倍
                    newThr = oldThr << 1; 
            }
            else if (oldThr > 0) 
            // 旧table没有数据并且旧的阈值大于0,设置旧的阈值为扩容后的hashmap容量
                newCap = oldThr;
            else {
            // 旧table没有数据并且旧的阈值=0,设置默认容量16,默认阈值为16*0.75=12 
                newCap = DEFAULT_INITIAL_CAPACITY;
                newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
            }
            if (newThr == 0) {
                // 计算扩容以后的阈值
                float ft = (float)newCap * loadFactor;
                // 扩容后的阈值
                newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
                          (int)ft : Integer.MAX_VALUE);
            }
            threshold = newThr;
            // 构建一个新的table，容量为扩容后容量
            Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
            table = newTab;
            if (oldTab != null) {
            // 如果原来的table有数据，则将数据复制到新的table中
                for (int j = 0; j < oldCap; ++j) {
                    Node<K,V> e;
                    // 获取数组的第j个链表
                    if ((e = oldTab[j]) != null) {
                        oldTab[j] = null;
                        if (e.next == null)
                            // 如果链表只有一个节点，则进行直接赋值
                            newTab[e.hash & (newCap - 1)] = e;
                        else if (e instanceof TreeNode)
                            // 红黑树赋值
                            ((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
                        else { 
                            // 进行链表复制
                            // 方法比较特殊： 它并没有重新计算元素在数组中的位置
                            // 而是采用了 原始位置加原数组长度的方法计算得到位置
                            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);
                            //新表索引：hash & (newCap - 1)---》低x位为Index
                            //旧表索引：hash & (oldCap - 1)---》低x-1位为Index
                            //newCap = oldCap << 1
                            //举例说明：resize()之前为低x-1位为Index，resize()之后为低x位为Index
                            //则所有Entry中，hash值第x位为0的，不需要哈希到新位置，只需要呆在当前索引下的新位置j
                            //hash值第x位为1的，需要哈希到新位置，新位置为j+oldCap
    
                            if (loTail != null) {
                                loTail.next = null;
                                newTab[j] = loHead;
                            }
                            if (hiTail != null) {
                                hiTail.next = null;
                                newTab[j + oldCap] = hiHead;
                            }
                        }
                    }
                }
            }
            return newTab;
        }
    
        /** * 链表树形化（红黑树） */
        final void treeifyBin(Node<K,V>[] tab, int hash) {
            int n, index; Node<K,V> e;
            /* * 如果元素数组为空 或者 数组长度小于 树结构化的最小限制 * MIN_TREEIFY_CAPACITY 默认值64，对于这个值可以理解为：如果元素数组长度小于这个值，没有必要去进行结构转换 * 当一个数组位置上集中了多个键值对，那是因为这些key的hash值和数组长度取模之后结果相同。（并不是因为这些key的hash值相同） * 因为hash值相同的概率不高，所以可以通过扩容的方式，来使得最终这些key的hash值在和新的数组长度取模之后，拆分到多个数组位置*上。 */
            if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
                resize();
            // 如果元素数组长度已经大于等于了 MIN_TREEIFY_CAPACITY，那么就有必要进行结构转换了
            // 根据hash值和数组长度进行取模运算后，得到链表的首节点
            else if ((e = tab[index = (n - 1) & hash]) != null) {
                TreeNode<K,V> hd = null, tl = null;
                do {
                    // 将该节点转换为 树节点
                    TreeNode<K,V> p = replacementTreeNode(e, null);
                    // 如果尾节点为空，说明还没有根节点
                    if (tl == null)
                        // 首节点（根节点）指向 当前节点
                        hd = p;
                    else {
                        // 尾节点不为空，以下两行是一个双向链表结构
                        // 当前树节点的前一个节点指向尾节点
                        p.prev = tl;
                        // 尾节点的后一个节点指向当前节点
                        tl.next = p;
                    }
                    // 把当前节点设为尾节点
                    tl = p;
                } while ((e = e.next) != null);
                // 到目前为止 也只是把Node对象转换成了TreeNode对象，把单向链表转换成了双向链表
                // 把转换后的双向链表，替换原来位置上的单向链表
                if ((tab[index] = hd) != null)
                    hd.treeify(tab);
            }
        }
    
        /** * 将m中所有元素存入当前hashmap中,若存在相同的key,则替换 */
        public void putAll(Map<? extends K, ? extends V> m) {
            putMapEntries(m, true);
        }
    
        /** * 删除key对应的节点,返回节点值value,不存在节点返回null */
        public V remove(Object key) {
            Node<K,V> e;
            return (e = removeNode(hash(key), key, null, false, true)) == null ?
                null : e.value;
        }
    
        /** * 从当前hashmap中删除key对应的节点 * * @param hash key的hash值 * @param key key值 * @param value 如果指定了matchValue=true,需要同时匹配value * @param matchValue 如果为true,只有key和value完全匹配才能删除 * @param movable 如果指定false,则在删除后不移动其他节点,默认true */
        final Node<K,V> removeNode(int hash, Object key, Object value,
                                   boolean matchValue, boolean movable) {
            // tab:当前hashmap的table结构
            // p:根据hash定位到table位置的当前节点
            // n:tab长度
            // index:key对应节点在table数组中的下标
            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:需要删除的节点
                // e:用于遍历的节点变量
                // k:节点变量的key
                // v:要删除节点的值
                Node<K,V> node = null, e; K k; V v;
                if (p.hash == hash &&
                    ((k = p.key) == key || (key != null && key.equals(k))))
                    // 要删除的节点为链表的首节点
                    node = p;
                else if ((e = p.next) != null) {
                    // 链表存在其他节点
                    if (p instanceof TreeNode)
                        // 链表首节点p是红黑树类型，根据红黑树算法查询需要删除的节点
                        node = ((TreeNode<K,V>)p).getTreeNode(hash, key);
                    else {
                        // 否则根据链表算法遍历找到需要删除的节点
                        do {
                            if (e.hash == hash &&
                                ((k = e.key) == key ||
                                 (key != null && key.equals(k)))) {
                                // 找到需要删除的节点,跳出循环
                                node = e;
                                break;
                            }
                            // 将要删除的前一个节点赋值给p,用于后续删除后移动链表指针
                            p = e;
                        } while ((e = e.next) != null);
                    }
                }
                if (node != null && (!matchValue || (v = node.value) == value ||
                                     (value != null && value.equals(v)))) {
                    // 节点类型为红黑树类型,按照红黑树算法删除节点,并移动其他节点
                    if (node instanceof TreeNode)
                        ((TreeNode<K,V>)node).removeTreeNode(this, tab, movable);
                    // 要删除的节点为链表头节点（该链表只有一个节点）
                    else if (node == p)
                        // 移动链表
                        tab[index] = node.next;
                    else
                        // 删除node节点(通过改变p.next的指向为node的下一个节点来删除node节点)
                        p.next = node.next;
                    // 当前hashmap修改计数器加1
                    ++modCount;
                    // 当前hashmap元素个数减1
                    --size;
                    afterNodeRemoval(node);
                    // 返回删除的节点
                    return node;
                }
            }
            return null;
        }
    
        /** * 清空当前hashmap中所有元素,并设置size=0 */
        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;
            }
        }
    
        /** * 判定当前hashmap中是否存在包含value值的键值对 */
        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) {
                    // 外层循环遍历table数组
                    for (Node<K,V> e = tab[i]; e != null; e = e.next) {
                        // 内层循环遍历tab[i]表示的链表
                        if ((v = e.value) == value ||
                            (value != null && value.equals(v)))
                            // 一旦找到即返回true,否则遍历完后返回false
                            return true;
                    }
                }
            }
            // table为null或者当前hashmap没有元素或者遍历后未找到匹配的value,返回false
            return false;
        }
    
        /** * 返回包含所有key值的Set集合 */
        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();
                }
            }
        }
    
        /** * 和keySet()方法有点相似,返回的是所有的value集合 */
        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();
                }
            }
        }
    
        /** * 对返回当前hashmap的Map.Entry<K,V>集合,若对当前hashmap作出修改,会同时反映在该集合上 */
        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();
                }
            }
        }
    
        /** *获取key对应的value,若不存在则返回默认值(传入参数defaultValue) */
    
        @Override
        public V getOrDefault(Object key, V defaultValue) {
            Node<K,V> e;
            return (e = getNode(hash(key), key)) == null ? defaultValue : e.value;
        }
    
        /** *key对应的节点不存在则添加;若存在,则不替换,并返回已存在的值 */
        @Override
        public V putIfAbsent(K key, V value) {
            return putVal(hash(key), key, value, true, true);
        }
    
        /** *删除key-value对应的节点,此方法需要严格匹配key和value才能删除,删除成功返回true */
        @Override
        public boolean remove(Object key, Object value) {
            return removeNode(hash(key), key, value, true, true) != null;
        }
    
        /** *替换key对应的值,需要严格匹配key和oldValue才能替换新值 */
        @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;
        }
    
        /** *替换key对应的值,只要找到key对应的节点即可替换新值 */
        @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;
        }
    
        /** * Map接口的实现类如HashMap,ConcurrentHashMap,HashTable等继承了此方法，通过此方法可以构建JAVA本地缓存，降低程序的计算量，程序的复杂度，使代码简洁，易懂。 * 此方法首先判断缓存MAP中是否存在指定key的值，如果不存在，会自动调用mappingFunction(key)计算key的value，然后将key = value放入到缓存Map,java8会使用thread-safe的方式从cache中存取记录 */
        @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;
                }
            }
            // 到此为止，上面代码实现通过key查找value,找到即返回,没找到执行下面通过mappingFunction函数计算key对应的value,并存入当前hashmap
            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;
        }
    
        /** * 通过key查找数据,若不存在,方法返回null; * 若存在,（1）新值不为null,存储新值并返回;(2)计算出来的新值为null,将key对应的节点从当前hashmap中删除 */
        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);
            // key对应数据存在且不为null
            if ((e = getNode(hash, key)) != null &&
                (oldValue = e.value) != null) {
                // 通过函数重新计算key对应的value
                V v = remappingFunction.apply(key, oldValue);
                if (v != null) {
                    e.value = v;
                    afterNodeAccess(e);
                    return v;
                }
                else
                    // 若重新计算的value为null,将节点移除
                    removeNode(hash, key, null, false, true);
            }
            // key对应数据不存在
            return null;
        }
        /** * 通过key查找数据,若不存在,(1)计算得到的新值为null,方法返回null;（2）计算得到的新值不为null,存储新值并返回 * 若存在,（1）新值不为null,存储新值并返回;(2)计算出来的新值为null,将key对应的节点从当前hashmap中删除 */
        @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;
            // 判断是否需要扩容
            if (size > threshold || (tab = table) == null ||
                (n = tab.length) == 0)
                n = (tab = resize()).length;
            // 通过key的hash值能定位到数据处于table中的位置
            if ((first = tab[i = (n - 1) & hash]) != null) {
                if (first instanceof TreeNode)
                    // 用红黑树算法查找节点
                    // t用来记录红黑树根节点
                    old = (t = (TreeNode<K,V>)first).getTreeNode(hash, key);
                else {
                    Node<K,V> e = first; K k;
                    // 链表遍历查找节点
                    do {
                        if (e.hash == hash &&
                            ((k = e.key) == key || (key != null && key.equals(k)))) {
                            old = e;
                            break;
                        }
                        // 累加树形化计数器,便于后续判断是否需要将链表转换成红黑树
                        ++binCount;
                    } while ((e = e.next) != null);
                }
            }
            // 取得key对应的旧值
            V oldValue = (old == null) ? null : old.value;
            // 重新计算key对应的值v
            V v = remappingFunction.apply(key, oldValue);
            if (old != null) {
                // key在当前hashmap中存在
                if (v != null) {
                    // 重新计算的新值v不为null,替换旧值
                    old.value = v;
                    afterNodeAccess(old);
                }
                else
                    // 重新计算的新值v=null,将key对应节点移除
                    removeNode(hash, key, null, false, true);
            }
            // key在当前hashmap中不存在
            else if (v != null) {
                if (t != null)
                    // 红黑树加入新节点
                    t.putTreeVal(this, tab, hash, key, v);
                else {
                    // 链表加入新节点
                    tab[i] = newNode(hash, key, v, first);
                    // 链表加入新节点后,判断是否需要树形化
                    if (binCount >= TREEIFY_THRESHOLD - 1)
                        treeifyBin(tab, hash);
                }
                // 当前hashmap修改计数器加1
                ++modCount;
                // 当前hashmap大小加1
                ++size;
                afterNodeInsertion(true);
            }
            return v;
        }
    
        /** * 功能大部分与compute相同，不同之处在于BiFunction中apply的参数，入参为oldValue、value，调用merge时根据两个value进行逻辑处理并返回value。 */
        @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;
            // 判断是否需要扩容
            if (size > threshold || (tab = table) == null ||
                (n = tab.length) == 0)
                // 扩容
                n = (tab = resize()).length;
            // 查找key对应节点
            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);
                }
            }
            //节点存在
            if (old != null) {
                V v;
                if (old.value != null)
                    // 旧值不为null,根据入参value和旧值重新计算得到新值
                    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;
            }
            // 此处的if似乎是多余的？方法第一行就做了value判null处理
            if (value != null) {
                if (t != null)
                    // 红黑树加入新节点
                    t.putTreeVal(this, tab, hash, key, value);
                else {
                    // 链表加入新节点
                    tab[i] = newNode(hash, key, value, first);
                    if (binCount >= TREEIFY_THRESHOLD - 1)
                        treeifyBin(tab, hash);
                }
                ++modCount;
                ++size;
                afterNodeInsertion(true);
            }
            return value;
        }
    
        /** * 调用此方法时实现BiConsumer接口重写void accept(Object o, Object o2)方法，其中o为key，o2为value，可根据自己的实现对map中所有数据进行处理 */
        @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();
            }
        }
    
        /** * 调用此方法时重写BiFunction的Object apply(Object o, Object o2)方法，其中o为key，o2为value，根据重写方法逻辑进行重新赋值。 */
        @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();
            }
        }
    
        /** * 返回当前hashmap的一个浅拷贝 */
        @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);
            }
            // table = null;
            // entrySet = null;
            // keySet = null;
            // values = null;
            // modCount = 0;
            // threshold = 0;
            // size = 0;
            result.reinitialize();
            // 将当前hashmap所有节点存入新的hashmap
            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;
        }
    
        /** * Save the state of the <tt>HashMap</tt> instance to a stream (i.e., * serialize it). * * @serialData The <i>capacity</i> of the HashMap (the length of the * bucket array) is emitted (int), followed by the * <i>size</i> (an int, the number of key-value * mappings), followed by the key (Object) and value (Object) * for each key-value mapping. The key-value mappings are * emitted in no particular order. */
        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);
        }
    
        /** * Reconstitute the {@code HashMap} instance from a stream (i.e., * deserialize it). */
        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);
                @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. * @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(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 || 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(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;
            }
        }
    
    }