implements Map<K, V>, 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<K, V> implements Map.Entry<K, V> {

// hash存储key的hashCode

final int hash;

// final:一个键值对的key不可改变

final K key;

V value;

//指向下个节点的引用

Node<K, V> next;

//构造函数

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 -------------- */

/**

static final int hash(Object key) {

int h;

//计算key的hashCode, h = Objects.hashCode(key)

//h >>> 16表示对h无符号右移16位，高位补0，然后h与h >>> 16按位异或

return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);

}

/**

static Class<?> comparableClassFor(Object x) {

if (x instanceof Comparable) {

Class<?> c;

Type[] ts, as;

Type t;

ParameterizedType p;

if ((c = x.getClass()) == String.class) // bypass checks

return c;

if ((ts = c.getGenericInterfaces()) != null) {

for (int i = 0; i < ts.length; ++i) {

if (((t = ts[i]) instanceof ParameterizedType) &&

((p = (ParameterizedType) t).getRawType() ==

Comparable.class) &&

(as = p.getActualTypeArguments()) != null &&

as.length == 1 && as[0] == c) // type arg is c

return c;

}

}

}

return null;

}

/**

@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) {

//先移位再或运算，最终保证返回值是2的整数幂

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;

}

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

/**

transient Node<K, V>[] table;

/**

transient Set<Map.Entry<K, V>> entrySet;

/**

transient int size;

/**

transient int modCount;

/**

int threshold;

/**

final float loadFactor;

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

/**

public HashMap(int initialCapacity, float loadFactor) {

if (initialCapacity < 0)

throw new IllegalArgumentException("Illegal initial capacity: " +

initialCapacity);

if (initialCapacity > MAXIMUM_CAPACITY)

initialCapacity = MAXIMUM_CAPACITY;

if (loadFactor <= 0 || Float.isNaN(loadFactor))

throw new IllegalArgumentException("Illegal load factor: " +

loadFactor);

this.loadFactor = loadFactor;

this.threshold = tableSizeFor(initialCapacity);

}

/**

public HashMap(int initialCapacity) {

this(initialCapacity, DEFAULT_LOAD_FACTOR);

}

/**

public HashMap() {

this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted

}

/**

public HashMap(Map<? extends K, ? extends V> m) {

this.loadFactor = DEFAULT_LOAD_FACTOR;

putMapEntries(m, false);

}

/**

final void putMapEntries(Map<? extends K, ? extends V> m, boolean evict) {

int s = m.size();

//如果参数map不为空

if (s > 0) {

// 判断table是否已经初始化

if (table == null) { // pre-size

// 未初始化，s为m的实际元素个数

float ft = ((float) s / loadFactor) + 1.0F;

int t = ((ft < (float) MAXIMUM_CAPACITY) ?

(int) ft : MAXIMUM_CAPACITY);

// 计算得到的t大于阈值，则初始化阈值

if (t > threshold)

//根据容量初始化临界值

threshold = tableSizeFor(t);

// 已初始化，并且m元素个数大于阈值，进行扩容处理

} else if (s > threshold)

//扩容处理

resize();

// 将m中的所有元素添加至HashMap中

for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {

K key = e.getKey();

V value = e.getValue();

putVal(hash(key), key, value, false, evict);

}

}

}

/**

public int size() {

return size;

}

/**

public boolean isEmpty() {

return size == 0;

}

/**

public V get(Object key) {

Node<K, V> e;

//根据key及其hash值查询node节点，如果存在，则返回该节点的value值

return (e = getNode(hash(key), key)) == null ? null : e.value;

}

/**

final Node<K, V> getNode(int hash, Object key) {

Node<K, V>[] tab;

Node<K, V> first, e;

int n;

K k;

//如果哈希表不为空，而且key对应的桶上不为空

if ((tab = table) != null && (n = tab.length) > 0 &&

(first = tab[(n - 1) & hash]) != null) {

//如果桶中的第一个节点就和指定参数hash和key匹配上了

if (first.hash == hash && // always check first node

((k = first.key) == key || (key != null && key.equals(k))))

//返回桶中的第一个节点

return first;

//如果桶中的第一个节点没有匹配上，而且有后续节点

if ((e = first.next) != null) {

//如果当前的桶采用红黑树，则调用红黑树的get方法去获取节点

if (first instanceof TreeNode)

return ((TreeNode<K, V>) first).getTreeNode(hash, key);

//如果当前的桶不采用红黑树，即桶中节点结构为链式结构

do {

//遍历链表，直到key匹配

if (e.hash == hash &&

((k = e.key) == key || (key != null && key.equals(k))))

return e;

} while ((e = e.next) != null);

}

}

//如果哈希表为空，或者没有找到节点，返回null

return null;

}

/**

public boolean containsKey(Object key) {

return getNode(hash(key), key) != null;

}

/**

public V put(K key, V value) {

// 倒数第二个参数false：表示允许旧值替换

// 最后一个参数true：表示HashMap不处于创建模式

return putVal(hash(key), key, value, false, true);

}

/**

final V putVal(int hash, K key, V value, boolean onlyIfAbsent,

boolean evict) {

Node<K, V>[] tab;

Node<K, V> p;

int n, i;

//如果哈希表为空，调用resize()创建一个哈希表，并用变量n记录哈希表长度

if ((tab = table) == null || (n = tab.length) == 0)

n = (tab = resize()).length;

/**

if ((p = tab[i = (n - 1) & hash]) == null)

//直接将键值对插入到map中即可

tab[i] = newNode(hash, key, value, null);

else {// 桶中已经存在元素

Node<K, V> e;

K k;

// 比较桶中第一个元素(数组中的结点)的hash值相等，key相等

if (p.hash == hash &&

((k = p.key) == key || (key != null && key.equals(k))))

// 将第一个元素赋值给e，用e来记录

e = p;

// 当前桶中无该键值对，且桶是红黑树结构，按照红黑树结构插入

else if (p instanceof TreeNode)

e = ((TreeNode<K, V>) p).putTreeVal(this, tab, hash, key, value);

// 当前桶中无该键值对，且桶是链表结构，按照链表结构插入到尾部

else {

for (int binCount = 0; ; ++binCount) {

// 遍历到链表尾部

if ((e = p.next) == null) {

p.next = newNode(hash, key, value, null);

// 检查链表长度是否达到阈值，达到将该槽位节点组织形式转为红黑树

if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st

treeifyBin(tab, hash);

break;

}

// 链表节点的<key, value>与put操作<key, value>相同时，不做重复操作，跳出循环

if (e.hash == hash &&

((k = e.key) == key || (key != null && key.equals(k))))

break;

p = e;

}

}

// 找到或新建一个key和hashCode与插入元素相等的键值对，进行put操作

if (e != null) { // existing mapping for key

// 记录e的value

V oldValue = e.value;

/**

if (!onlyIfAbsent || oldValue == null)

e.value = value;

// 访问后回调

afterNodeAccess(e);

// 返回旧值

return oldValue;

}

}

// 更新结构化修改信息

++modCount;

// 键值对数目超过阈值时，进行rehash

if (++size > threshold)

resize();

// 插入后回调

afterNodeInsertion(evict);

return null;

}

/**

final Node<K, V>[] resize() {

//新建oldTab数组保存扩容前的数组table

Node<K, V>[] oldTab = table;

//获取原来数组的长度

int oldCap = (oldTab == null) ? 0 : oldTab.length;

//原来数组扩容的临界值

int oldThr = threshold;

int newCap, newThr = 0;

//如果扩容前的容量 > 0

if (oldCap > 0) {

//如果原来的数组长度大于最大值(2^30)

if (oldCap >= MAXIMUM_CAPACITY) {

//扩容临界值提高到正无穷

threshold = Integer.MAX_VALUE;

//无法进行扩容，返回原来的数组

return oldTab;

//如果现在容量的两倍小于MAXIMUM_CAPACITY且现在的容量大于DEFAULT_INITIAL_CAPACITY

} else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&

oldCap >= DEFAULT_INITIAL_CAPACITY)

//临界值变为原来的2倍

newThr = oldThr << 1;

} else if (oldThr > 0) //如果旧容量 <= 0，而且旧临界值 > 0

//数组的新容量设置为老数组扩容的临界值

newCap = oldThr;

else { //如果旧容量 <= 0，且旧临界值 <= 0，新容量扩充为默认初始化容量，新临界值为DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY

newCap = DEFAULT_INITIAL_CAPACITY;//新数组初始容量设置为默认值

newThr = (int) (DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);//计算默认容量下的阈值

}

// 计算新的resize上限

if (newThr == 0) {//在当上面的条件判断中，只有oldThr > 0成立时，newThr == 0

//ft为临时临界值，下面会确定这个临界值是否合法，如果合法，那就是真正的临界值

float ft = (float) newCap * loadFactor;

//当新容量< MAXIMUM_CAPACITY且ft < (float)MAXIMUM_CAPACITY，新的临界值为ft，否则为Integer.MAX_VALUE

newThr = (newCap < MAXIMUM_CAPACITY && ft < (float) MAXIMUM_CAPACITY ?

(int) ft : Integer.MAX_VALUE);

}

//将扩容后hashMap的临界值设置为newThr

threshold = newThr;

//创建新的table，初始化容量为newCap

@SuppressWarnings({"rawtypes", "unchecked"})

Node<K, V>[] newTab = (Node<K, V>[]) new Node[newCap];

//修改hashMap的table为新建的newTab

table = newTab;

//如果旧table不为空，将旧table中的元素复制到新的table中

if (oldTab != null) {

//遍历旧哈希表的每个桶，将旧哈希表中的桶复制到新的哈希表中

for (int j = 0; j < oldCap; ++j) {

Node<K, V> e;

//如果旧桶不为null，使用e记录旧桶

if ((e = oldTab[j]) != null) {

//将旧桶置为null

oldTab[j] = null;

//如果旧桶中只有一个node

if (e.next == null)

//将e也就是oldTab[j]放入newTab中e.hash & (newCap - 1)的位置

newTab[e.hash & (newCap - 1)] = e;

//如果旧桶中的结构为红黑树

else if (e instanceof TreeNode)

//将树中的node分离

((TreeNode<K, V>) e).split(this, newTab, j, oldCap);

else { //如果旧桶中的结构为链表,链表重排，jdk1.8做的一系列优化

Node<K, V> loHead = null, loTail = null;

Node<K, V> hiHead = null, hiTail = null;

Node<K, V> next;

//遍历整个链表中的节点

do {

next = e.next;

// 原索引

if ((e.hash & oldCap) == 0) {

if (loTail == null)

loHead = e;

else

loTail.next = e;

loTail = e;

} else {// 原索引+oldCap

if (hiTail == null)

hiHead = e;

else

hiTail.next = e;

hiTail = e;

}

} while ((e = next) != null);

// 原索引放到bucket里

if (loTail != null) {

loTail.next = null;

newTab[j] = loHead;

}

// 原索引+oldCap放到bucket里

if (hiTail != null) {

hiTail.next = null;

newTab[j + oldCap] = hiHead;

}

}

}

}

}

return newTab;

}

/**

final void treeifyBin(Node<K, V>[] tab, int hash) {

int n, index;

Node<K, V> e;

//如果桶数组table为空，或者桶数组table的长度小于MIN_TREEIFY_CAPACITY，不符合转化为红黑树的条件

if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)

//扩容

resize();

//如果符合转化为红黑树的条件，而且hash对应的桶不为null

else if ((e = tab[index = (n - 1) & hash]) != null) {

// 红黑树的头、尾节点

TreeNode<K, V> hd = null, tl = null;

//遍历链表

do {

//替换链表node为树node，建立双向链表

TreeNode<K, V> p = replacementTreeNode(e, null);

// 确定树头节点

if (tl == null)

hd = p;

else {

p.prev = tl;

tl.next = p;

}

tl = p;

} while ((e = e.next) != null);

//遍历链表插入每个节点到红黑树

if ((tab[index] = hd) != null)

hd.treeify(tab);

}

}

/**

public void putAll(Map<? extends K, ? extends V> m) {

putMapEntries(m, true);

}

/**

public V remove(Object key) {

Node<K, V> e;

//根据key来删除node。removeNode方法的具体实现在下面

return (e = removeNode(hash(key), key, null, false, true)) == null ?

null : e.value;

}

/**

final Node<K, V> removeNode(int hash, Object key, Object value,

boolean matchValue, boolean movable) {

Node<K, V>[] tab;

Node<K, V> p;

int n, index;

//如果数组table不为空且key映射到的桶不为空

if ((tab = table) != null && (n = tab.length) > 0 &&

(p = tab[index = (n - 1) & hash]) != null) {

Node<K, V> node = null, e;

K k;

V v;

//如果桶上第一个node的就是要删除的node

if (p.hash == hash &&

((k = p.key) == key || (key != null && key.equals(k))))

//记录桶上第一个node

node = p;

else if ((e = p.next) != null) {//如果桶内不止一个node

//如果桶内的结构为红黑树

if (p instanceof TreeNode)

//记录key映射到的node

node = ((TreeNode<K, V>) p).getTreeNode(hash, key);

else {//如果桶内的结构为链表

do {//遍历链表，找到key映射到的node

if (e.hash == hash &&

((k = e.key) == key ||

(key != null && key.equals(k)))) {

//记录key映射到的node

node = e;

break;

}

p = e;

} while ((e = e.next) != null);

}

}

//如果得到的node不为null且(matchValue为false||node.value和参数value匹配)

if (node != null && (!matchValue || (v = node.value) == value ||

(value != null && value.equals(v)))) {

//如果桶内的结构为红黑树

if (node instanceof TreeNode)

//使用红黑树的删除方法删除node

((TreeNode<K, V>) node).removeTreeNode(this, tab, movable);

else if (node == p)//如果桶的第一个node的就是要删除的node

//删除node

tab[index] = node.next;

else//如果桶内的结构为链表，使用链表删除元素的方式删除node

p.next = node.next;

++modCount;//结构性修改次数+1

--size;//哈希表大小-1

afterNodeRemoval(node);

return node;//返回被删除的node

}

}

return null;//如果数组table为空或key映射到的桶为空，返回null。

}

/**

public void clear() {

Node<K, V>[] tab;

modCount++;

if ((tab = table) != null && size > 0) {

size = 0;

for (int i = 0; i < tab.length; ++i)

tab[i] = null;

}

}

/**

public boolean containsValue(Object value) {

Node<K, V>[] tab;

V v;

if ((tab = table) != null && size > 0) {

//遍历数组table

for (int i = 0; i < tab.length; ++i) {

//遍历桶中的node

for (Node<K, V> e = tab[i]; e != null; e = e.next) {

if ((v = e.value) == value ||

(value != null && value.equals(v)))

return true;

}

}

}

return false;

}

/**

public Set<K> keySet() {

Set<K> ks = keySet;

if (ks == null) {

ks = new KeySet();

keySet = ks;

}

return ks;

}

/**

final class KeySet extends AbstractSet<K> {

public final int size() {

return size;

}

public final void clear() {

HashMap.this.clear();

}

public final Iterator<K> iterator() {

return new KeyIterator();

}

public final boolean contains(Object o) {

return containsKey(o);

}

public final boolean remove(Object key) {

return removeNode(hash(key), key, null, false, true) != null;

}

public final Spliterator<K> spliterator() {

return new KeySpliterator<>(HashMap.this, 0, -1, 0, 0);

}

public final void forEach(Consumer<? super K> action) {

Node<K, V>[] tab;

if (action == null)

throw new NullPointerException();

if (size > 0 && (tab = table) != null) {

int mc = modCount;

for (int i = 0; i < tab.length; ++i) {

for (Node<K, V> e = tab[i]; e != null; e = e.next)

action.accept(e.key);

}

if (modCount != mc)

throw new ConcurrentModificationException();

}

}

}

/**

public Collection<V> values() {

Collection<V> vs = values;

if (vs == null) {

vs = new Values();

values = vs;

}

return vs;

}

/**

final class Values extends AbstractCollection<V> {

public final int size() {

return size;

}

public final void clear() {

HashMap.this.clear();

}

public final Iterator<V> iterator() {

return new ValueIterator();

}

public final boolean contains(Object o) {

return containsValue(o);

}

public final Spliterator<V> spliterator() {

return new ValueSpliterator<>(HashMap.this, 0, -1, 0, 0);

}

public final void forEach(Consumer<? super V> action) {

Node<K, V>[] tab;

if (action == null)

throw new NullPointerException();

if (size > 0 && (tab = table) != null) {

int mc = modCount;

for (int i = 0; i < tab.length; ++i) {

for (Node<K, V> e = tab[i]; e != null; e = e.next)

action.accept(e.value);

}

if (modCount != mc)

throw new ConcurrentModificationException();

}

}

}

/**

public Set<Map.Entry<K, V>> entrySet() {

Set<Map.Entry<K, V>> es;

return (es = entrySet) == null ? (entrySet = new EntrySet()) : es;

}

/**

final class EntrySet extends AbstractSet<Map.Entry<K, V>> {

public final int size() {

return size;

}

public final void clear() {

HashMap.this.clear();

}

public final Iterator<Map.Entry<K, V>> iterator() {

return new EntryIterator();

}

public final boolean contains(Object o) {

if (!(o instanceof Map.Entry))

return false;

Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;

Object key = e.getKey();

Node<K, V> candidate = getNode(hash(key), key);

return candidate != null && candidate.equals(e);

}

public final boolean remove(Object o) {

if (o instanceof Map.Entry) {

Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;

Object key = e.getKey();

Object value = e.getValue();

return removeNode(hash(key), key, value, true, true) != null;

}

return false;

}

public final Spliterator<Map.Entry<K, V>> spliterator() {

return new EntrySpliterator<>(HashMap.this, 0, -1, 0, 0);

}

public final void forEach(Consumer<? super Map.Entry<K, V>> action) {

Node<K, V>[] tab;

if (action == null)

throw new NullPointerException();

if (size > 0 && (tab = table) != null) {

int mc = modCount;

for (int i = 0; i < tab.length; ++i) {

for (Node<K, V> e = tab[i]; e != null; e = e.next)

action.accept(e);

}

if (modCount != mc)

throw new ConcurrentModificationException();

}

}

}

// JDK8重写的方法

/**

@Override

public V getOrDefault(Object key, V defaultValue) {

Node<K, V> e;

return (e = getNode(hash(key), key)) == null ? defaultValue : e.value;

}

/**

@Override

public V putIfAbsent(K key, V value) {

return putVal(hash(key), key, value, true, true);

}

/**