HashMap最全中文注释+源码（个人总结）

package java.util;

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

public class HashMap extends AbstractMap
        implements Map, Cloneable, Serializable {

    private static final long serialVersionUID = 362498820763181265L;

    
    static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16

    
    static final int MAXIMUM_CAPACITY = 1 << 30;

    
    static final float DEFAULT_LOAD_FACTOR = 0.75f;

    
    static final int TREEIFY_THRESHOLD = 8;

    
    static final int UNTREEIFY_THRESHOLD = 6;

    
    static final int MIN_TREEIFY_CAPACITY = 64;

    
    static class Node implements Map.Entry {
        final int hash;
        final K key;
        V value;
        java.util.HashMap.Node next;

        Node(int hash, K key, V value, java.util.HashMap.Node 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 final int hash(Object key) {
        int h;
        return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
    }

    
    static Class comparableClassFor(Object x) {
        if (x instanceof Comparable) {
            Class c; Type[] ts, as; ParameterizedType p;
            if ((c = x.getClass()) == String.class) // bypass checks
                return c;
            if ((ts = c.getGenericInterfaces()) != null) {
                for (Type t : ts) {
                    if ((t 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;
    }

    
    @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));
    }

    
    static final int tableSizeFor(int cap) {
        int n = -1 >>> Integer.numberOfLeadingZeros(cap - 1);
        return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
    }

    

    
    transient java.util.HashMap.Node[] table;

    
    transient Set> entrySet;

    
    transient int size;

    
    transient int modCount;

    
    int threshold;

    
    final float loadFactor;

    

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

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

    
    public HashMap() {
        this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
    }

    
    public HashMap(Map m) {
        this.loadFactor = DEFAULT_LOAD_FACTOR;
        putMapEntries(m, false);
    }

    
    final void putMapEntries(Map m, boolean evict) {
        int s = m.size();
        //如果m中有元素，才继续执行
        if (s > 0) {
            //如果hashMap还没有初始化
            if (table == null) { // pre-size
                float ft = ((float)s / loadFactor) + 1.0F;
                int t = ((ft < (float)MAXIMUM_CAPACITY) ?
                        (int)ft : MAXIMUM_CAPACITY);
                //按照装填因子算出t，如果t大于threshold，就先把threshold扩大
                if (t > threshold)
                    threshold = tableSizeFor(t);
            }
            //如果hashMap初始化过了；如果要装入的元素大于threshold，就执行方法resize，这个方法中决定是否扩容
            else if (s > threshold)
                resize();


            //然后循环m对象，放入hashMap
            for (Map.Entry e : m.entrySet()) {
                K key = e.getKey();
                V value = e.getValue();
                putVal(hash(key), key, value, false, evict);
            }
        }
    }

    
    public int size() {
        return size;
    }

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

    
    public V get(Object key) {
        java.util.HashMap.Node e;
        return (e = getNode(hash(key), key)) == null ? null : e.value;
    }

    
    final java.util.HashMap.Node getNode(int hash, Object key) {
        //Node数组tab；Node对象first，e；int对象n；Key的类型的k
        java.util.HashMap.Node[] tab; java.util.HashMap.Node first, e; int n; K k;
        //如果hashMap中有元素
        if ((tab = table) != null && (n = tab.length) > 0 &&
                (first = tab[(n - 1) & hash]) != null) {
            //如果第一个Node对象就是要找的对象，就返回第一个Node对象
            if (first.hash == hash && // always check first node
                    ((k = first.key) == key || (key != null && key.equals(k))))
                return first;
            //如果第一个不是，并且还有下一个
            if ((e = first.next) != null) {
                //如果第一个Node对象是TreeNode类型（已经变成红黑树时），就按TreeNode的获取方式
                if (first instanceof java.util.HashMap.TreeNode)
                    return ((java.util.HashMap.TreeNode)first).getTreeNode(hash, key);
                //否则，如果不是红黑树，就循环遍历，寻找key相同的Node对象
                do {
                    if (e.hash == hash &&
                            ((k = e.key) == key || (key != null && key.equals(k))))
                        return e;
                } while ((e = e.next) != null);
            }
        }
        return null;
    }

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

    
    public V put(K key, V value) {
        return putVal(hash(key), key, value, false, true);
    }

    
    final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                   boolean evict) {
        //Node数组tab；Node对象p；int类型的n,i;
        java.util.HashMap.Node[] tab; java.util.HashMap.Node p; int n, i;
        //如果hashMap中有元素，就调用resize方法（这个方法中决定是否扩容）
        if ((tab = table) == null || (n = tab.length) == 0)
            n = (tab = resize()).length;

        //如果在数组第i个位置上没有Node对象，就新建一个node对象（i是key根据hash值算出来的、应该在hashMap数组中的位置）
        //hashMap是数组+链表(红黑树)的结构
        if ((p = tab[i = (n - 1) & hash]) == null)
            tab[i] = newNode(hash, key, value, null);
        //否则，数组第i个位置有Node对象了
        else {
            //Node对象e；key类型的k
            java.util.HashMap.Node e; K k;
            //如果数组第i个位置的Node对象的hash值等于传入的key的hash值并且Node对象的key等于传入的key
            //那就先让e=数组第i个位置的Node对象
            if (p.hash == hash &&
                    ((k = p.key) == key || (key != null && key.equals(k))))
                e = p;

            //否则如果数组第i个位置的Node对象属于TreeNode对象(红黑树)，那就按照红黑树的方法放入元素
            else if (p instanceof java.util.HashMap.TreeNode)
                e = ((java.util.HashMap.TreeNode)p).putTreeval(this, tab, hash, key, value);

            //否则，说明是普通的Node对象(并且key不相等)
            else {
                //开始遍历，寻找map中是否有这个key存在
                for (int binCount = 0; ; ++binCount) {
                    //如果遍历完，没有下一个Node对象了
                    if ((e = p.next) == null) {
                        //那就新建一个Node对象，挂在p.next上
                        p.next = newNode(hash, key, value, null);
                        //如果链长大于等于8个了(这里是8-1=7，但是算上first，就是8个了)
                        if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                            //就把这个链转成红黑树
                            treeifyBin(tab, hash);
                        break;
                    }
                    //如果遍历时，找到了key（说明这个key已经在map中存在了）
                    //那就停止循环，此时e是那个匹配key成功的Node对象(上面的e=p.next给e赋的值)
                    if (e.hash == hash &&
                            ((k = e.key) == key || (key != null && key.equals(k))))
                        break;

                    //这个是每次循环的最后，让p=e；注意break后这句就不会执行了
                    p = e;
                }
            }
            //如果e不为空（说明map中已经有传入的key存在了，这个e的key就是传入的key）
            if (e != null) { // existing mapping for key
                V oldValue = e.value;
                //这里看是否是onlyIfAbsent；看是否要替换这个value
                if (!onlyIfAbsent || oldValue == null)
                    e.value = value;

                //linkedHashMap用的方法，hashMap不用
                afterNodeAccess(e);

                return oldValue;
            }
        }



        //用于快速失败的变量++
        ++modCount;
        //如果放入一个元素，超过了需要扩容的个数(threshold是map容量*0.75后的值)，就执行resize方法
        if (++size > threshold)
            resize();

        //linkedHashMap用的方法，hashMap不用
        afterNodeInsertion(evict);
        return null;
    }

    
    final java.util.HashMap.Node[] resize() {
        //旧的hashMap的数组对象（数组+链表的数组）
        java.util.HashMap.Node[] oldTab = table;
        //旧的hashMap的数组长度（容量）
        int oldCap = (oldTab == null) ? 0 : oldTab.length;
        //旧的扩容变量（默认length*0.75）
        int oldThr = threshold;

        int newCap, newThr = 0;
        //如果旧的hashMap长度>0
        if (oldCap > 0) {
            //如果超过最大容量，就使用最大整数
            if (oldCap >= MAXIMUM_CAPACITY) {
                threshold = Integer.MAX_VALUE;
                return oldTab;
            }
            //否则如果小于最大容量并且旧的hashMap长度大于16
            else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
                    oldCap >= DEFAULT_INITIAL_CAPACITY)
                //就扩大变量newThr(*2)
                newThr = oldThr << 1; // double threshold
        }

        //否则如果旧的扩容变量>0（可能是初始化时，旧map长度为0，但是有oldThr）
        else if (oldThr > 0) // initial capacity was placed in threshold
            newCap = oldThr;

        //否则
        else {               // zero initial threshold signifies using defaults
            //新的map的数组的长度，取默认值，16
            newCap = DEFAULT_INITIAL_CAPACITY;
            //新的map的扩容变量threshold，取默认值，16*0.75=12
            newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
        }

        //如果新的扩容变量为0
        if (newThr == 0) {
            //新的map的数组的容量*装填因子
            float ft = (float)newCap * loadFactor;
            //重新给新的扩容变量赋值
            newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
                    (int)ft : Integer.MAX_VALUE);
        }

        threshold = newThr;

        //使用newCap创建新的map的Node数组
        @SuppressWarnings({"rawtypes","unchecked"})
        java.util.HashMap.Node[] newTab = (java.util.HashMap.Node[])new java.util.HashMap.Node[newCap];
        table = newTab;

        //如果旧map数组还有元素，那就得把旧的元素装入新的map数组中
        if (oldTab != null) {
            //遍历旧Node数组
            for (int j = 0; j < oldCap; ++j) {
                java.util.HashMap.Node e;
                if ((e = oldTab[j]) != null) {
                    oldTab[j] = null;
                    //如果node对象没有下一个了，就直接装入新Node数组
                    if (e.next == null)
                        newTab[e.hash & (newCap - 1)] = e;
                    //否则如果旧的Node对象是TreeNode类型(红黑树)
                    else if (e instanceof java.util.HashMap.TreeNode)
                        //那就用处理红黑树的方法
                        ((java.util.HashMap.TreeNode)e).split(this, newTab, j, oldCap);
                    //否则
                    else { // preserve order
                        //用两组Node对象，一组是loHead,loTail
                        //另一组是hiHead,hiTail
                        //大概就是把旧的一条链分成新的两条链，可以减少链长，提高查找效率
                        java.util.HashMap.Node loHead = null, loTail = null;
                        java.util.HashMap.Node hiHead = null, hiTail = null;
                        java.util.HashMap.Node next;
                        do {
                            next = e.next;
                            //按位与运算，看保存到哪一组
                            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;
    }

    
    final void treeifyBin(java.util.HashMap.Node[] tab, int hash) {
        int n, index; java.util.HashMap.Node e;
        if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
            resize();
        else if ((e = tab[index = (n - 1) & hash]) != null) {
            java.util.HashMap.TreeNode hd = null, tl = null;
            do {
                java.util.HashMap.TreeNode p = replacementTreeNode(e, null);
                if (tl == null)
                    hd = p;
                else {
                    p.prev = tl;
                    tl.next = p;
                }
                tl = p;
            } while ((e = e.next) != null);
            if ((tab[index] = hd) != null)
                hd.treeify(tab);
        }
    }

    
    public void putAll(Map m) {
        putMapEntries(m, true);
    }

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

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

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

    
    public boolean containsValue(Object value) {
        java.util.HashMap.Node[] tab; V v;
        if ((tab = table) != null && size > 0) {
            for (java.util.HashMap.Node e : tab) {
                for (; e != null; e = e.next) {
                    if ((v = e.value) == value ||
                            (value != null && value.equals(v)))
                        return true;
                }
            }
        }
        return false;
    }

    
    public Set keySet() {
        Set ks = keySet;
        if (ks == null) {
            ks = new java.util.HashMap.KeySet();
            keySet = ks;
        }
        return ks;
    }

    
    final class KeySet extends AbstractSet {
        public final int size()                 { return size; }
        public final void clear()               { java.util.HashMap.this.clear(); }
        public final Iterator iterator()     { return new java.util.HashMap.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 spliterator() {
            return new java.util.HashMap.KeySpliterator<>(java.util.HashMap.this, 0, -1, 0, 0);
        }
        public final void forEach(Consumer action) {
            java.util.HashMap.Node[] tab;
            if (action == null)
                throw new NullPointerException();
            if (size > 0 && (tab = table) != null) {
                int mc = modCount;
                for (java.util.HashMap.Node e : tab) {
                    for (; e != null; e = e.next)
                        action.accept(e.key);
                }
                if (modCount != mc)
                    throw new ConcurrentModificationException();
            }
        }
    }

    
    public Collection values() {
        Collection vs = values;
        if (vs == null) {
            vs = new java.util.HashMap.Values();
            values = vs;
        }
        return vs;
    }

    
    final class Values extends AbstractCollection {
        public final int size()                 { return size; }
        public final void clear()               { java.util.HashMap.this.clear(); }
        public final Iterator iterator()     { return new java.util.HashMap.ValueIterator(); }
        public final boolean contains(Object o) { return containsValue(o); }
        public final Spliterator spliterator() {
            return new java.util.HashMap.ValueSpliterator<>(java.util.HashMap.this, 0, -1, 0, 0);
        }
        public final void forEach(Consumer action) {
            java.util.HashMap.Node[] tab;
            if (action == null)
                throw new NullPointerException();
            if (size > 0 && (tab = table) != null) {
                int mc = modCount;
                for (java.util.HashMap.Node e : tab) {
                    for (; e != null; e = e.next)
                        action.accept(e.value);
                }
                if (modCount != mc)
                    throw new ConcurrentModificationException();
            }
        }
    }

    
    public Set> entrySet() {
        Set> es;
        return (es = entrySet) == null ? (entrySet = new java.util.HashMap.EntrySet()) : es;
    }

    
    final class EntrySet extends AbstractSet> {
        public final int size()                 { return size; }
        public final void clear()               { java.util.HashMap.this.clear(); }
        public final Iterator> iterator() {
            return new java.util.HashMap.EntryIterator();
        }
        public final boolean contains(Object o) {
            if (!(o instanceof Map.Entry))
                return false;
            Map.Entry e = (Map.Entry) o;
            Object key = e.getKey();
            java.util.HashMap.Node 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> spliterator() {
            return new java.util.HashMap.EntrySpliterator<>(java.util.HashMap.this, 0, -1, 0, 0);
        }
        public final void forEach(Consumer> action) {
            java.util.HashMap.Node[] tab;
            if (action == null)
                throw new NullPointerException();
            if (size > 0 && (tab = table) != null) {
                int mc = modCount;
                for (java.util.HashMap.Node e : tab) {
                    for (; e != null; e = e.next)
                        action.accept(e);
                }
                if (modCount != mc)
                    throw new ConcurrentModificationException();
            }
        }
    }

    // Overrides of JDK8 Map extension methods

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

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

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

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

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

    
    @Override
    public V computeIfAbsent(K key,
                             Function mappingFunction) {
        if (mappingFunction == null)
            throw new NullPointerException();
        int hash = hash(key);
        java.util.HashMap.Node[] tab; java.util.HashMap.Node first; int n, i;
        int binCount = 0;
        java.util.HashMap.TreeNode t = null;
        java.util.HashMap.Node 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 java.util.HashMap.TreeNode)
                old = (t = (java.util.HashMap.TreeNode)first).getTreeNode(hash, key);
            else {
                java.util.HashMap.Node 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;
            }
        }
        int mc = modCount;
        V v = mappingFunction.apply(key);
        if (mc != modCount) { throw new ConcurrentModificationException(); }
        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);
            //如果链长大于等于8个了(这里是8-1=7，但是算上first，就是8个了)
            if (binCount >= TREEIFY_THRESHOLD - 1)
                //就把这个链转成红黑树
                treeifyBin(tab, hash);
        }
        modCount = mc + 1;
        ++size;
        afterNodeInsertion(true);
        return v;
    }

    
    @Override
    public V computeIfPresent(K key,
                              BiFunction remappingFunction) {
        if (remappingFunction == null)
            throw new NullPointerException();
        java.util.HashMap.Node e; V oldValue;
        int hash = hash(key);
        if ((e = getNode(hash, key)) != null &&
                (oldValue = e.value) != null) {
            int mc = modCount;
            V v = remappingFunction.apply(key, oldValue);
            if (mc != modCount) { throw new ConcurrentModificationException(); }
            if (v != null) {
                e.value = v;
                afterNodeAccess(e);
                return v;
            }
            else
                removeNode(hash, key, null, false, true);
        }
        return null;
    }

    
    @Override
    public V compute(K key,
                     BiFunction remappingFunction) {
        if (remappingFunction == null)
            throw new NullPointerException();
        int hash = hash(key);
        java.util.HashMap.Node[] tab; java.util.HashMap.Node first; int n, i;
        int binCount = 0;
        java.util.HashMap.TreeNode t = null;
        java.util.HashMap.Node 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 java.util.HashMap.TreeNode)
                old = (t = (java.util.HashMap.TreeNode)first).getTreeNode(hash, key);
            else {
                java.util.HashMap.Node 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;
        int mc = modCount;
        V v = remappingFunction.apply(key, oldValue);
        if (mc != modCount) { throw new ConcurrentModificationException(); }
        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);
                //如果链长大于等于8个了(这里是8-1=7，但是算上first，就是8个了)
                if (binCount >= TREEIFY_THRESHOLD - 1)
                    //就把这个链转成红黑树
                    treeifyBin(tab, hash);
            }
            modCount = mc + 1;
            ++size;
            afterNodeInsertion(true);
        }
        return v;
    }

    
    @Override
    public V merge(K key, V value,
                   BiFunction remappingFunction) {
        if (value == null)
            throw new NullPointerException();
        if (remappingFunction == null)
            throw new NullPointerException();
        int hash = hash(key);
        java.util.HashMap.Node[] tab; java.util.HashMap.Node first; int n, i;
        int binCount = 0;
        java.util.HashMap.TreeNode t = null;
        java.util.HashMap.Node 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 java.util.HashMap.TreeNode)
                old = (t = (java.util.HashMap.TreeNode)first).getTreeNode(hash, key);
            else {
                java.util.HashMap.Node 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) {
                int mc = modCount;
                v = remappingFunction.apply(old.value, value);
                if (mc != modCount) {
                    throw new ConcurrentModificationException();
                }
            } 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);
                //如果链长大于等于8个了(这里是8-1=7，但是算上first，就是8个了)
                if (binCount >= TREEIFY_THRESHOLD - 1)
                    //就把这个链转成红黑树
                    treeifyBin(tab, hash);
            }
            ++modCount;
            ++size;
            afterNodeInsertion(true);
        }
        return value;
    }

    
    @Override
    public void forEach(BiConsumer action) {
        java.util.HashMap.Node[] tab;
        if (action == null)
            throw new NullPointerException();
        if (size > 0 && (tab = table) != null) {
            int mc = modCount;
            for (java.util.HashMap.Node e : tab) {
                for (; e != null; e = e.next)
                    action.accept(e.key, e.value);
            }
            if (modCount != mc)
                throw new ConcurrentModificationException();
        }
    }


    
    @Override
    public void replaceAll(BiFunction function) {
        java.util.HashMap.Node[] tab;
        if (function == null)
            throw new NullPointerException();
        if (size > 0 && (tab = table) != null) {
            int mc = modCount;
            for (java.util.HashMap.Node e : tab) {
                for (; e != null; e = e.next) {
                    e.value = function.apply(e.key, e.value);
                }
            }
            if (modCount != mc)
                throw new ConcurrentModificationException();
        }
    }

    
    // Cloning and serialization

    
    @SuppressWarnings("unchecked")
    @Override
    public Object clone() {
        java.util.HashMap result;
        try {
            result = (java.util.HashMap)super.clone();
        } catch (CloneNotSupportedException e) {
            // this shouldn't happen, since we are Cloneable
            throw new InternalError(e);
        }
        result.reinitialize();
        result.putMapEntries(this, false);
        return result;
    }

    
    // These methods are also used when serializing HashSets
    final float loadFactor() { return loadFactor; }
    
    final int capacity() {
        return (table != null) ? table.length :
                (threshold > 0) ? threshold :
                        DEFAULT_INITIAL_CAPACITY;
    }

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

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

            // Check Map.Entry[].class since it's the nearest public type to
            // what we're actually creating.
            SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Map.Entry[].class, cap);
            @SuppressWarnings({"rawtypes","unchecked"})
            java.util.HashMap.Node[] tab = (java.util.HashMap.Node[])new java.util.HashMap.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 {
        java.util.HashMap.Node next;        // next entry to return
        java.util.HashMap.Node current;     // current entry
        int expectedModCount;  // for fast-fail
        int index;             // current slot

        HashIterator() {
            expectedModCount = modCount;
            java.util.HashMap.Node[] 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 java.util.HashMap.Node nextNode() {
            java.util.HashMap.Node[] t;
            java.util.HashMap.Node 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() {
            java.util.HashMap.Node p = current;
            if (p == null)
                throw new IllegalStateException();
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            current = null;
            removeNode(p.hash, p.key, null, false, false);
            expectedModCount = modCount;
        }
    }

    final class KeyIterator extends java.util.HashMap.HashIterator
            implements Iterator {
        public final K next() { return nextNode().key; }
    }

    final class ValueIterator extends java.util.HashMap.HashIterator
            implements Iterator {
        public final V next() { return nextNode().value; }
    }

    final class EntryIterator extends java.util.HashMap.HashIterator
            implements Iterator> {
        public final Map.Entry next() { return nextNode(); }
    }

    
    // spliterators

    
    static class HashMapSpliterator {
        final java.util.HashMap map;
        java.util.HashMap.Node 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 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 m = map;
                est = m.size;
                expectedModCount = m.modCount;
                java.util.HashMap.Node[] 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
            extends java.util.HashMap.HashMapSpliterator
            implements Spliterator {
        KeySpliterator(java.util.HashMap m, int origin, int fence, int est,
                       int expectedModCount) {
            super(m, origin, fence, est, expectedModCount);
        }

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

        public void forEachRemaining(Consumer action) {
            int i, hi, mc;
            if (action == null)
                throw new NullPointerException();
            java.util.HashMap m = map;
            java.util.HashMap.Node[] 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)) {
                java.util.HashMap.Node 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 action) {
            int hi;
            if (action == null)
                throw new NullPointerException();
            java.util.HashMap.Node[] 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
            extends java.util.HashMap.HashMapSpliterator
            implements Spliterator {
        ValueSpliterator(java.util.HashMap m, int origin, int fence, int est,
                         int expectedModCount) {
            super(m, origin, fence, est, expectedModCount);
        }

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

        public void forEachRemaining(Consumer action) {
            int i, hi, mc;
            if (action == null)
                throw new NullPointerException();
            java.util.HashMap m = map;
            java.util.HashMap.Node[] 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)) {
                java.util.HashMap.Node 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 action) {
            int hi;
            if (action == null)
                throw new NullPointerException();
            java.util.HashMap.Node[] 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
            extends java.util.HashMap.HashMapSpliterator
            implements Spliterator> {
        EntrySpliterator(java.util.HashMap m, int origin, int fence, int est,
                         int expectedModCount) {
            super(m, origin, fence, est, expectedModCount);
        }

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

        public void forEachRemaining(Consumer> action) {
            int i, hi, mc;
            if (action == null)
                throw new NullPointerException();
            java.util.HashMap m = map;
            java.util.HashMap.Node[] 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)) {
                java.util.HashMap.Node 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> action) {
            int hi;
            if (action == null)
                throw new NullPointerException();
            java.util.HashMap.Node[] tab = map.table;
            if (tab != null && tab.length >= (hi = getFence()) && index >= 0) {
                while (current != null || index < hi) {
                    if (current == null)
                        current = tab[index++];
                    else {
                        java.util.HashMap.Node 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
    

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

    
    java.util.HashMap.Node replacementNode(java.util.HashMap.Node p, java.util.HashMap.Node next) {
        return new java.util.HashMap.Node<>(p.hash, p.key, p.value, next);
    }

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

    
    java.util.HashMap.TreeNode replacementTreeNode(java.util.HashMap.Node p, java.util.HashMap.Node next) {
        return new java.util.HashMap.TreeNode<>(p.hash, p.key, p.value, next);
    }

    
    void reinitialize() {
        table = null;
        entrySet = null;
        keySet = null;
        values = null;
        modCount = 0;
        threshold = 0;
        size = 0;
    }

    // Callbacks to allow linkedHashMap post-actions

    
    void afterNodeAccess(java.util.HashMap.Node p) { }
    void afterNodeInsertion(boolean evict) { }
    void afterNodeRemoval(java.util.HashMap.Node p) { }

    
    void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException {
        java.util.HashMap.Node[] tab;
        if (size > 0 && (tab = table) != null) {
            for (java.util.HashMap.Node e : tab) {
                for (; e != null; e = e.next) {
                    s.writeObject(e.key);
                    s.writeObject(e.value);
                }
            }
        }
    }

    
    // Tree bins

    
    static final class TreeNode extends linkedHashMap.Entry {
        java.util.HashMap.TreeNode parent;  // red-black tree links
        java.util.HashMap.TreeNode left;
        java.util.HashMap.TreeNode right;
        java.util.HashMap.TreeNode prev;    // needed to unlink next upon deletion
        boolean red;
        TreeNode(int hash, K key, V val, java.util.HashMap.Node next) {
            super(hash, key, val, next);
        }

        
        final java.util.HashMap.TreeNode root() {
            for (java.util.HashMap.TreeNode r = this, p;;) {
                if ((p = r.parent) == null)
                    return r;
                r = p;
            }
        }

        
        static  void moveRootToFront(java.util.HashMap.Node[] tab, java.util.HashMap.TreeNode root) {
            int n;
            if (root != null && tab != null && (n = tab.length) > 0) {
                int index = (n - 1) & root.hash;
                java.util.HashMap.TreeNode first = (java.util.HashMap.TreeNode)tab[index];
                if (root != first) {
                    java.util.HashMap.Node rn;
                    tab[index] = root;
                    java.util.HashMap.TreeNode rp = root.prev;
                    if ((rn = root.next) != null)
                        ((java.util.HashMap.TreeNode)rn).prev = rp;
                    if (rp != null)
                        rp.next = rn;
                    if (first != null)
                        first.prev = root;
                    root.next = first;
                    root.prev = null;
                }
                assert checkInvariants(root);
            }
        }

        
        final java.util.HashMap.TreeNode find(int h, Object k, Class kc) {
            java.util.HashMap.TreeNode p = this;
            do {
                int ph, dir; K pk;
                java.util.HashMap.TreeNode 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;
        }

        
        final java.util.HashMap.TreeNode getTreeNode(int h, Object k) {
            return ((parent != null) ? root() : this).find(h, k, null);
        }

        
        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;
        }

        
        final void treeify(java.util.HashMap.Node[] tab) {
            java.util.HashMap.TreeNode root = null;
            for (java.util.HashMap.TreeNode x = this, next; x != null; x = next) {
                next = (java.util.HashMap.TreeNode)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 (java.util.HashMap.TreeNode 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);

                        java.util.HashMap.TreeNode 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);
        }

        
        final java.util.HashMap.Node untreeify(java.util.HashMap map) {
            java.util.HashMap.Node hd = null, tl = null;
            for (java.util.HashMap.Node q = this; q != null; q = q.next) {
                java.util.HashMap.Node p = map.replacementNode(q, null);
                if (tl == null)
                    hd = p;
                else
                    tl.next = p;
                tl = p;
            }
            return hd;
        }

        
        final java.util.HashMap.TreeNode putTreeval(java.util.HashMap map, java.util.HashMap.Node[] tab,
                                                         int h, K k, V v) {
            Class kc = null;
            boolean searched = false;
            java.util.HashMap.TreeNode root = (parent != null) ? root() : this;
            for (java.util.HashMap.TreeNode 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) {
                        java.util.HashMap.TreeNode 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);
                }

                java.util.HashMap.TreeNode xp = p;
                if ((p = (dir <= 0) ? p.left : p.right) == null) {
                    java.util.HashMap.Node xpn = xp.next;
                    java.util.HashMap.TreeNode 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)
                        ((java.util.HashMap.TreeNode)xpn).prev = x;
                    moveRootToFront(tab, balanceInsertion(root, x));
                    return null;
                }
            }
        }

        
        final void removeTreeNode(java.util.HashMap map, java.util.HashMap.Node[] tab,
                                  boolean movable) {
            int n;
            if (tab == null || (n = tab.length) == 0)
                return;
            int index = (n - 1) & hash;
            java.util.HashMap.TreeNode first = (java.util.HashMap.TreeNode)tab[index], root = first, rl;
            java.util.HashMap.TreeNode succ = (java.util.HashMap.TreeNode)next, pred = prev;
            if (pred == null)
                tab[index] = first = succ;
            else
                pred.next = succ;
            if (succ != null)
                succ.prev = pred;
            if (first == null)
                return;
            if (root.parent != null)
                root = root.root();
            if (root == null
                    || (movable
                    && (root.right == null
                    || (rl = root.left) == null
                    || rl.left == null))) {
                tab[index] = first.untreeify(map);  // too small
                return;
            }
            java.util.HashMap.TreeNode p = this, pl = left, pr = right, replacement;
            if (pl != null && pr != null) {
                java.util.HashMap.TreeNode 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
                java.util.HashMap.TreeNode sr = s.right;
                java.util.HashMap.TreeNode pp = p.parent;
                if (s == pr) { // p was s's direct parent
                    p.parent = s;
                    s.right = p;
                }
                else {
                    java.util.HashMap.TreeNode 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) {
                java.util.HashMap.TreeNode 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;
            }

            java.util.HashMap.TreeNode r = p.red ? root : balanceDeletion(root, replacement);

            if (replacement == p) {  // detach
                java.util.HashMap.TreeNode 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);
        }

        
        final void split(java.util.HashMap map, java.util.HashMap.Node[] tab, int index, int bit) {
            java.util.HashMap.TreeNode b = this;
            // Relink into lo and hi lists, preserving order
            //准备两组树节点（一棵树拆分成两个用）
            java.util.HashMap.TreeNode loHead = null, loTail = null;
            java.util.HashMap.TreeNode hiHead = null, hiTail = null;
            int lc = 0, hc = 0;
            for (java.util.HashMap.TreeNode e = b, next; e != null; e = next) {
                next = (java.util.HashMap.TreeNode)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) {
                //如果元素小于等于6，就没必要继续使用树结构了，所以换成链表结构
                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) {
                //如果元素小于等于6，就没必要继续使用树结构了，所以换成链表结构
                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  java.util.HashMap.TreeNode rotateLeft(java.util.HashMap.TreeNode root,
                                                                java.util.HashMap.TreeNode p) {
            java.util.HashMap.TreeNode 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  java.util.HashMap.TreeNode rotateRight(java.util.HashMap.TreeNode root,
                                                                 java.util.HashMap.TreeNode p) {
            java.util.HashMap.TreeNode 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  java.util.HashMap.TreeNode balanceInsertion(java.util.HashMap.TreeNode root,
                                                                      java.util.HashMap.TreeNode x) {
            x.red = true;
            for (java.util.HashMap.TreeNode 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  java.util.HashMap.TreeNode balanceDeletion(java.util.HashMap.TreeNode root,
                                                                     java.util.HashMap.TreeNode x) {
            for (java.util.HashMap.TreeNode 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 {
                        java.util.HashMap.TreeNode 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 {
                        java.util.HashMap.TreeNode 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;
                        }
                    }
                }
            }
        }

        
        static  boolean checkInvariants(java.util.HashMap.TreeNode t) {
            java.util.HashMap.TreeNode tp = t.parent, tl = t.left, tr = t.right,
                    tb = t.prev, tn = (java.util.HashMap.TreeNode)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;
        }
    }

}

1.初始化hashMap时，hashMap的容量为大于传入大小的最接近的2^n；
如果不指定容量，默认就是16（DEFAULT_INITIAL_CAPACITY）；
例如传入15，hashMap的容量就是16；
注意，初始化hashMap的容量大小与装填因子loadFactor无关。

2.当执行put、putAll等方法时，才会利用装填因子loadFactor算出threshold变量的值；
threshold=map容量*loadFactor(默认0.75)；
当放入元素导致使用容量超过threshold时，就扩容。

3.keySet,values,entrySet 这三个集合中是不保存数据的，但是可以用来遍历，是一种节约空间的写法（元素在table变量中保存就够了）

4.链表转红黑树的判断值是8；红黑树转链表的判断值是6。

5.MIN_TREEIFY_CAPACITY = 64，表示map至少有64个以上元素的时候，才考虑是否转红黑树。