package com.xinye.web.controller.redandblack;/*
* Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
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.AbstractMap;
import java.util.Map;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Consumer;
import java.util.function.Function;
/**
* 基于哈希表的Map接口实现lei 。
* 该类实现提供了所有可选的map操作且允许null值和null键:
* (HashMap 类大致等同于hashtable，除了它是不同步(线程不安全)且允许为空。）
* 此类不保证先后的顺序是无须的；特别是，它不能保证会一直保持不变(扩容的时候顺序会产生变化)。)
* 该类提供的的基本方法get和put，假设将元素 hash后适当地分散在存储桶(buckets)中。迭代结束查看集合视图需要的时间
* 与HashMap实例的“容量”（存储桶数）加上其大小（键值映射数）成比例。因此，这俩参数对迭代性能是影响很大。
* HashMap的实例有两个参数影响 性能：初始容量和负载系数。这个初始容量是哈希表中的存储桶数，
* 初始容量只是创建哈希表时的容量。负载因子是在哈希表的容量自动增加之前，允许哈希表获得的满容量的度量。
* 当哈希表中的条目数超过加载因子和 在当前容量下，哈希表将被重新灰化（即重建内部数据结构），
* 重构号哈希表的存储桶数（size）大约是之前的存储桶数的两倍。
* ----------------------------------------------------------------------------
* 一般来说，默认的荷载系数（.75）提供了一个很好的时间和空间成本之间的权衡。较高的值会减少空间开销，
* 但会增加查找成本（反映在HashMap类的大多数操作中，包括get和put）。中的预期条目数在设置初始容量时，
* 应考虑map及其负载系数，以尽量减少再灰化操作的次数。如果使用量除以初始容量小于负载系数 ，将不会发生再扩容操作！
* 如果许多映射要存储在HashMap中 例如，创建具有足够大容量的映射将允许更有效地存储映射，
* 而不是让它根据需要执行自动重新灰化以扩展表。请注意，使用多个具有相同{@code hashCode()}的键
* (hash冲突：那么他们确定的索引位置就相同，这时判断他们的key是否相同，如果不相同，这时就是产生了hash冲突)
* 肯定会降低任何哈希表的性能。为了改善影响，当键是{@link Comparable}时(当键实现了Comparable类的compareTo方法)，
* 这个类可以使用键之间的比较顺序来帮助打破联系提高性能。
* ----------------------------------------------------------------------------
* 请注意，此实现不同步(线程不安全)。
* 如果多个线程同时访问哈希映射，并且至少有一个线程在结构上修改了该映射，则必须在外部对其进行同步。
* （结构修改是添加或删除一个或多个映射的任何操作；仅更改与实例已包含的键相关联的值不是结构修改。）
* 这通常通过在自然封装映射的某个对象上进行同步来完成。
* 如果不存在此类对象，则应使用{@link Collections#synchronizedMap Collections.synchronizedMap}
* 方法“包装”映射。最好在创建时执行此操作，以防止意外地对映射进行非同步访问：
* Map m=Collections.synchronizedMap(new HashMap(...))；
* ----------------------------------------------------------------------------
* 这个类的所用的“collection”里的的迭代器都是快速失败的：如果在迭代器创建之后的任何时候对映射进行了结构上的修改，
* 除了通过迭代器自己的remove方法之外，迭代器将抛出{@link ConcurrentModificationException}。
* 因此，在面对并发修改时，迭代器会快速而干净地失败，而不是在将来某个不确定的时间冒着任意的、不确定的行为的风险。
* ----------------------------------------------------------------------------
* 注意，不能保证迭代器的fail-fast行为(fail-fast机制)，因为通常情况下，在存在不同步的并发修改的情况下，
* 不可能做出任何硬保证。 fail-fast机制在尽最大努力的基础上抛出ConcurrentModificationException。
* 因此，编写依赖于此异常的程序以确保其正确性是错误的：迭代器的快速失败行为应该只用于检测错误
*/
public class HashMap extends AbstractMap implements Map, Cloneable, Serializable {
private static final long serialVersionUID = 362498820763181265L;
/*
* map一般作为一个个桶组成的hash表,当数量很多的时候,会转变成TreeNodes(树节点),这样结构上类似TreeMap.
* TreeNodes可能进行了转化,使用起来和其他非TreeNodes一样,但是提供了较快速度的遍历效率.
* 然而大多数场景下出现很多元素拥挤的情况不会出现,可是检查是否是tree bins将会在使用各个方法时消耗性能.
* 那就要看这个判断的性能是不是需要很大消耗了.
* 我们知道hashmap的实现时数组+链表,在链表拥挤情况时,将它传变成树,有助于查询,但是如果是加减元素就不好说了.
* -------------------------
* Tree bins排序核心依赖hashCode,这里说的排序其实就是算出自己在数组中的下标,
* 如果有两个元素都class C implements Comparable,compareTo 方法会被用于排序.
* (我们使用反射去见这个类型,方法:comparableClassFor)
* 无论在不同hash值或和排序的情况下都证明算法复杂度是 O(log n),所以tree bins 带来的复杂度是值得的.
* 因此,即时在hashCode出来的值不够充分的分散,因为是树的原因,性能变差的过程也会比较平滑.
* --------------------------
* 当一个桶里有足够多的节点是才会将结构转成tree,目前TREEIFY_THRESHOLD默认设置为8,当变少的时候,也会转换为
* 原来平的链表结构.如果hashCodes是均匀分散的,这种转成tree基本用不到. 理想的分布应该是泊松分布.
* 这里有点难理解,查了很多资料,有了以下详细解释: 这里提到泊松分布,可以看wiki,也可以看下推荐的博文:
* http://www.ruanyifeng.com/blog/2015/06/poisson-distribution.html
* 在文档上无法用数学公式和图片,所以下面对注释众提到的公式进行解析:
* exp : 指数函数
* pow : 乘方运算
* factorial : 阶乘
* (exp(-0.5) * pow(0.5, k) / factorial(k)) 这个公式是可以对应到泊松分布的公式的.
* 这个0.5的意思是表示在这里假定元素数量占桶数量的百分50,而threshold是0.75,元素在某个桶里的概率是0.5.
* 所以我们以这个概率为基础数据算出,桶里有1-8个元素的概率,如数据.当有8个元素在一个桶里时的概率非常低,
* 在这里也解释了,如果出现需要将链表转成树的情况出现,已经表示不合理的场景出现了.
* --------------
* 一般树的根是第一个加入的node,也有其他情况,比如remove掉了root,不过可以重新分配出root.
* 这里加一下信息:
* redis中,在处理这种情况时是把新加入的元素放在链表的头部,在它的场景里最近加入的元素越容易被用到
* 所有的内部方法都可以接受一个hashcode来做为参数,如此内部调用的时候完全可以通过这个参数而不需要重新计算
* hashCodes.大部分内部方法也接受一个tab参数,一般这个有是现在的表的,在resizing或converting的时候也有可能代表新表或老表的.
*/
/**
* 默认初始capacity,必须是2的幂.
*/
static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16
/**
* The maximum capacity, used if a higher value is implicitly specified
* by either of the constructors with arguments.
* capacity最大值2的30幂次
*/
static final int MAXIMUM_CAPACITY = 1 << 30;
/**
* 负载因子
*/
static final float DEFAULT_LOAD_FACTOR = 0.75f;
/**
* The bin count threshold for using a tree rather than list for a
* bin. Bins are converted to trees when adding an element to a
* bin with at least this many nodes. The value must be greater
* than 2 and should be at least 8 to mesh with assumptions in
* tree removal about conversion back to plain bins upon
* shrinkage.
* 当一个链表上的元素到8个的时候,会转成树结构
*/
static final int TREEIFY_THRESHOLD = 8;
/**
* The bin count threshold for untreeifying a (split) bin during a
* resize operation. Should be less than TREEIFY_THRESHOLD, and at
* most 6 to mesh with shrinkage detection under removal.
* 当元素减小到6个时会从树转成链表
*/
static final int UNTREEIFY_THRESHOLD = 6;
/**
* The smallest table capacity for which bins may be treeified.
* (Otherwise the table is resized if too many nodes in a bin.)
* Should be at least 4 * TREEIFY_THRESHOLD to avoid conflicts
* between resizing and treeification thresholds.
* 当发生链表转树这种情况,需要满足capacity必须大于等于64(8的四倍)
* * 容量大于这个值时，表中的桶才能进行树形化
*/
static final int MIN_TREEIFY_CAPACITY = 64;
/**
* Basic hash bin node, used for most entries. (See below for
* TreeNode subclass, and in LinkedHashMap for its Entry subclass.)
* 这个就是核心数据结构,一个node对应一个key-value元素,hash表示自己在哪个桶里的,next表示链表结构.
*/
static class Node implements Map.Entry {
final int hash;
final K key;
V value;
Node next;
Node(int hash, K key, V value, 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 utilities -------------- */
/**
* Computes key.hashCode() and spreads (XORs) higher bits of hash
* to lower. Because the table uses power-of-two masking, sets of
* hashes that vary only in bits above the current mask will
* always collide. (Among known examples are sets of Float keys
* holding consecutive whole numbers in small tables.) So we
* apply a transform that spreads the impact of higher bits
* downward. There is a tradeoff between speed, utility, and
* quality of bit-spreading. Because many common sets of hashes
* are already reasonably distributed (so don't benefit from
* spreading), and because we use trees to handle large sets of
* collisions in bins, we just XOR some shifted bits in the
* cheapest possible way to reduce systematic lossage, as well as
* to incorporate impact of the highest bits that would otherwise
* never be used in index calculations because of table bounds.
* 代码中是将key的hashCode和高16位进行了异或操作
* 注意到我们table的长度必然为2的幂,这里有一点要注意在取模的操作里如果是和素数(质数)取模比和合数取模冲突的
* 概率要低.
* 合数既然可以由自身以外的数除尽,哪些可以相乘得到这个合数,这些乘数或乘数的倍数,都是潜在引起冲突的值.
* 所以作者解释了把高位的16位下移,做一个异或操作(XOR),保证了高位参与hash值取模时参加计算,这是在权衡了速度,
* 质量和实用性上进行的妥协.
*/
static final int hash(Object key) {
int h;
// 对key的hashCode得到值再修饰一下
return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}
/**
* Returns x's Class if it is of the form "class C implements
* Comparable", else null.
* 如果实现了Comparable，返回x的实际类型，也就是Class，否则返回null.
* 例子:public class AppVersion implements Comparable
*/
static Class comparableClassFor(Object x) {
if (x instanceof Comparable) {
Class c;
Type[] ts, as;
Type t;
ParameterizedType p;
if ((c = x.getClass()) == String.class) { // bypass checks
return c;
}
if ((ts = c.getGenericInterfaces()) != null) {
for (int i = 0; i < ts.length; ++i) {
if (((t = ts[i]) instanceof ParameterizedType) &&
((p = (ParameterizedType) t).getRawType() == Comparable.class) &&
(as = p.getActualTypeArguments()) != null &&
as.length == 1 && as[0] == c) { // type arg is c
return c;
}
}
}
}
return null;
}
/**
* Returns k.compareTo(x) if x matches kc (k's screened comparable
* class), else 0.
*/
@SuppressWarnings({ "rawtypes", "unchecked" }) // for cast to Comparable
static int compareComparables(Class kc, Object k, Object x) {
return (x == null || x.getClass() != kc ? 0 : ((Comparable) k).compareTo(x));
}
/**
* 返回一个2的幂大小的数,这个数比cap大.
*/
static final int tableSizeFor(int cap) {
/**
* 先解释或运算|=:
* int a = 5; // 0000 0101
* int b = 3; // 0000 0011
* a |= b; // 0000 00111
*/
/**
* 再解释且运算|=:
* int a = 5; // 0000 0101
* int b = 3; // 0000 0011
* a &= b; // 0000 0001
*/
/**
* 二级制中，与高位相对，表示二进制数字右边部分。
*/
// cap的二进制里低位全部转成1
// 解释一个:n |= n >>> 1 ==> n = n>>>1 | n
// 假设n= 0001 xxxx xxxx xxxx
// 计算:0001 xxxx xxxx xxxx | 0000 1xxx xxxx xxxx => 0001 1xxx xxxx xxxx
// 此时最高位就是两个连续的1,然后操作n |= n >>> 2,那么就变成 0001 111x xxxx xxxx
// 所以变1的节奏个数是:1 2 4 8 16 相加 31 刚好足够把32位的一个值低位全部变成1.
// 只不过cap最大也就是2的30次
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 -------------- */
/**
* The table, initialized on first use, and resized as
* necessary. When allocated, length is always a power of two.
* (We also tolerate length zero in some operations to allow
* bootstrapping mechanics that are currently not needed.)
* 所以我们说hashmap的核心数据结构就是一个装着node的数组 我们注意到字段使用transient修饰,不参与序列化,
* 可是hashmap继承Serializable.原因是hashcode操作依赖jvm所处的环境因素,不同环境可能有不同的hash值,
* 做一现成存储的内容既是序列化也无法通用.所以hashmap自己实现了writeObject和readObject
* 这里就需要知道java在序列化和反序列化一个类时是先调用writeObject和readObject,如果没有默认调用的
* 是ObjectOutputStream的defaultWriteObject以及ObjectInputStream的defaultReadObject方法
*/
transient Node[] table;
/**
* Holds cached entrySet(). Note that AbstractMap fields are used
* for keySet() and values().
*/
transient Set> entrySet;
/**
* The number of key-value mappings contained in this map.
* 记录有多少元素存进来了
*/
transient int size;
/**
* The number of times this HashMap has been structurally modified
* Structural modifications are those that change the number of mappings in
* the HashMap or otherwise modify its internal structure (e.g.,
* rehash). This field is used to make iterators on Collection-views of
* the HashMap fail-fast. (See ConcurrentModificationException).
* 前面提到过在迭代的时候如果改变了map的结构是要抛异常的,这个数用于记录改变的次数.
*/
transient int modCount;
/**
* The next size value at which to resize (capacity * load factor).
* 判断什么时候可以resize了
*
* @serial
*/
// (The javadoc description is true upon serialization.
// Additionally, if the table array has not been allocated, this
// field holds the initial array capacity, or zero signifying
// DEFAULT_INITIAL_CAPACITY.)
int threshold;
/**
* The load factor for the hash table.
* 负载因子
*
* @serial
*/
final float loadFactor;
/* ---------------- Public operations -------------- */
/**
* Constructs an empty HashMap with the specified initial
* capacity and load factor.
*
* @param initialCapacity
* the initial capacity
* @param loadFactor
* the load factor
* @throws IllegalArgumentException
* if the initial capacity is negative
* or the load factor is nonpositive
*/
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);
}
/**
* Constructs an empty HashMap with the specified initial
* capacity and the default load factor (0.75).
*
* @param initialCapacity
* the initial capacity.
* @throws IllegalArgumentException
* if the initial capacity is negative.
*/
public HashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
/**
* Constructs an empty HashMap with the default initial capacity
* (16) and the default load factor (0.75).
*/
public HashMap() {
this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted
}
/**
* Constructs a new HashMap with the same mappings as the
* specified Map. The HashMap is created with
* default load factor (0.75) and an initial capacity sufficient to
* hold the mappings in the specified Map.
* 参数为一个map的构造函数,新的HashMap负载因子为0.75,参数不能为null
*
* @param m
* the map whose mappings are to be placed in this map
* @throws NullPointerException
* if the specified map is null
*/
public HashMap(Map m) {
this.loadFactor = DEFAULT_LOAD_FACTOR;
putMapEntries(m, false);
}
/**
* Implements Map.putAll and Map constructor
* putAll也调用这个方法.evict为false时代表构造函数调用
*
* @param m
* the map
* @param evict
* false when initially constructing this map, else
* true (relayed to method afterNodeInsertion).
*/
final void putMapEntries(Map m, boolean evict) {
int s = m.size();
if (s > 0) {
if (table == null) { // pre-size
float ft = ((float) s / loadFactor) + 1.0F;
int t = ((ft < (float) MAXIMUM_CAPACITY) ? (int) ft : MAXIMUM_CAPACITY);
if (t > threshold)
threshold = tableSizeFor(t);
} else if (s > threshold) // 提前做了一次resize
resize();
for (Map.Entry e : m.entrySet()) {
K key = e.getKey();
V value = e.getValue();
// 调用内部put方法 hash(key)方法先处理下key
putVal(hash(key), key, value, false, evict);
}
}
}
/**
* Returns the number of key-value mappings in this map.
*
* @return the number of key-value mappings in this map
*/
public int size() {
return size;
}
/**
* Returns true if this map contains no key-value mappings.
*
* @return true if this map contains no key-value mappings
*/
public boolean isEmpty() {
return size == 0;
}
/**
* Returns the value to which the specified key is mapped,
* or {@code null} if this map contains no mapping for the key.
*
* More formally, if this map contains a mapping from a key
* {@code k} to a value {@code v} such that {@code (key==null ? k==null :
* key.equals(k))}, then this method returns {@code v}; otherwise
* it returns {@code null}. (There can be at most one such mapping.)
*
* A return value of {@code null} does not necessarily
* indicate that the map contains no mapping for the key; it's also
* possible that the map explicitly maps the key to {@code null}.
* The {@link #containsKey containsKey} operation may be used to
* distinguish these two cases.
* 获取key对应的value,这里返回null不一定代表map里没有这个元素,可能是value本来就是null.
*
* @see #put(Object, Object)
*/
public V get(Object key) {
Node e;
return (e = getNode(hash(key), key)) == null ? null : e.value;
}
/**
* Implements Map.get and related methods
*
* @param hash
* hash for key
* @param key
* the key
* @return the node, or null if none
*/
final Node getNode(int hash, Object key) {
Node[] tab;
Node first, e;
int n;
K k;
if ((tab = table) != null && (n = tab.length) > 0 &&
(first = tab[(n - 1) & hash]) != null) {
if (first.hash == hash && // always check first node
((k = first.key) == key || (key != null && key.equals(k))))
return first;
if ((e = first.next) != null) {
if (first instanceof TreeNode)
return ((TreeNode) first).getTreeNode(hash, key);
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
return e;
} while ((e = e.next) != null);
}
}
return null;
}
/**
* Returns true if this map contains a mapping for the
* specified key.
*
* @param key
* The key whose presence in this map is to be tested
* @return true if this map contains a mapping for the specified
* key.
*/
public boolean containsKey(Object key) {
return getNode(hash(key), key) != null;
}
/**
* Associates the specified value with the specified key in this map.
* If the map previously contained a mapping for the key, the old
* value is replaced.
*
* @param key
* key with which the specified value is to be associated
* @param value
* value to be associated with the specified key
* @return the previous value associated with key, or
* null if there was no mapping for key.
* (A null return can also indicate that the map
* previously associated null with key.)
*/
public V put(K key, V value) {
return putVal(hash(key), key, value, false, true);
}
/**
* Implements Map.put and related methods
* put方法调用.
* onlyIfAbsent参数用于putIfAbsent方法调用时使用true,表示是否替换
*
* @paramhash后的key值
* @param 原来的key
* @param value值
* @param 如果为true，则不更改现有值（key重复不覆盖原有的值）
* @param 钩子方法，这在HashMap中是个空方法，但是在其子类LinkedHashMap中会被Override
* @return 返回null 或者上一次的值
*/
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
boolean evict) {
Node[] tab;
Node p;
int n, i;
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length;// 若当前哈希数组table的长度为0，则进行扩容
if ((p = tab[i = (n - 1) & hash]) == null)// 确定输入的hash在哈希数组中对应的下标i
// 若数组该位置之前没有被占用，则新建一个节点放入，插入完成。
tab[i] = newNode(hash, key, value, null);
else {// 桶内已经有元素情况
Node e;
K k;
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
e = p;// 放入元素和头元素相同,进行替换
else if (p instanceof TreeNode)// 不相同,则判断是否为TreeNode
/**
* 若该位置的第一个节点p为TreeNode类型，说明这里存放的是一棵红黑树，p为根节点。
* 于是交给putTreeVal方法来完成后续操作，该方法下文会有详述
**/
e = ((TreeNode) p).putTreeVal(this, tab, hash, key, value);
else {
// 走到这里，说明p不匹配且是一个链表的头结点，该遍历链表了
// 链表的情况,这里是先进行循环,在循环的过程中判断出元素超过TREEIFY_THRESHOLD则进行treeifyBin操作
for (int binCount = 0;; ++binCount) {
/** e指向p的下一个节点 **/
if ((e = p.next) == null) {
// 当next是null的时候就是尾部了,这里就是把新放入的元素加到链表尾部的操作
p.next = newNode(hash, key, value, null);
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
// treeifyBin操作 转换成tree结构
/**
* 若插入后，该桶中的节点个数已达到了树化阈值
* 则对该桶进行树化。该部分源码下文会有详述
**/
treeifyBin(tab, hash);
break;
}
// 这里判断已经有相同key的元素
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
/**
* 匹配成功，我们需要用新的value来覆盖e节点
**/
break;
p = e; // 循环继续
}
}
// 若执行到此时e不为空，则说明在map中找到了与key相匹配的节点e
if (e != null) { // existing mapping for key
V oldValue = e.value;// 暂存e节点当前的值为oldValue
// 这里处理onlyIfAbsent,先新建一个node,然后再判断onlyIfAbsent,来决定是否替换原来的元素.
// 注意如果原来的元素的value是会替换掉的!
if (!onlyIfAbsent || oldValue == null)
e.value = value;
// 钩子方法 LinkedHashMap使用
afterNodeAccess(e);
return oldValue;
}
}
/**** --执行到此处说明没有匹配到已存在节点，一定是有新节点插入-- ****/
++modCount; // 结构操作数加一
// 触发resize
if (++size > threshold)
resize();// 插入后，map中的节点数加一，若此时已达阈值，则扩容
afterNodeInsertion(evict);// 同样的钩子方法，通知子类有新节点插入
return null;// 同样的钩子方法，通知子类有新节点插入
}
/**
* Initializes or doubles table size. If null, allocates in
* accord with initial capacity target held in field threshold.
* Otherwise, because we are using power-of-two expansion, the
* elements from each bin must either stay at same index, or move
* with a power of two offset in the new table.
* 初始化或倍增table的长度,因为长度遵守2的幂,所以元素的在resize后的新位置要么在远处要么移动2的幂次位置.
* resize是map核心算法之一,它决定这map在扩容时的性能.如果是一个膨胀速度快的map,对resize的要求就很高了.
*
* @return the table
*/
final Node[] resize() {
Node[] oldTab = table;
int oldCap = (oldTab == null) ? 0 : oldTab.length;
int oldThr = threshold;
int newCap, newThr = 0;
if (oldCap > 0) {
if (oldCap >= MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return oldTab;
} else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
oldCap >= DEFAULT_INITIAL_CAPACITY)
newThr = oldThr << 1; // double threshold
} else if (oldThr > 0) // initial capacity was placed in threshold
newCap = oldThr;
else { // zero initial threshold signifies using defaults
newCap = DEFAULT_INITIAL_CAPACITY;
newThr = (int) (DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
}
if (newThr == 0) {
float ft = (float) newCap * loadFactor;
newThr = (newCap < MAXIMUM_CAPACITY && ft < (float) MAXIMUM_CAPACITY ? (int) ft : Integer.MAX_VALUE);
}
threshold = newThr;
@SuppressWarnings({ "rawtypes", "unchecked" })
Node[] newTab = (Node[]) new Node[newCap];
table = newTab;
if (oldTab != null) {
for (int j = 0; j < oldCap; ++j) {
Node e;
if ((e = oldTab[j]) != null) {
oldTab[j] = null;
if (e.next == null)
newTab[e.hash & (newCap - 1)] = e;
else if (e instanceof TreeNode)
((TreeNode) e).split(this, newTab, j, oldCap);
else { // preserve order
Node loHead = null, loTail = null;
Node hiHead = null, hiTail = null;
Node next;
do {
next = e.next;
if ((e.hash & oldCap) == 0) {
if (loTail == null)
loHead = e;
else
loTail.next = e;
loTail = e;
} else {
if (hiTail == null)
hiHead = e;
else
hiTail.next = e;
hiTail = e;
}
} while ((e = next) != null);
if (loTail != null) {
loTail.next = null;
newTab[j] = loHead;
}
if (hiTail != null) {
hiTail.next = null;
newTab[j + oldCap] = hiHead;
}
}
}
}
}
return newTab;
}
/**
* Replaces all linked nodes in bin at index for given hash unless
* table is too small, in which case resizes instead.
* 将链表转成树结构,如果table还很小,就用resize操作.
*/
final void treeifyBin(Node[] tab, int hash) {
int n, index;
Node e;
if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
resize(); // 若table数组为空或其容量小于最小树化值，则用扩容取代树化
else if ((e = tab[index = (n - 1) & hash]) != null) { // 定位到hash对应的桶位，头结点记为e
TreeNode hd = null;
TreeNode tl = null; // 声明两个指针分别指向链表头尾节点
do {
TreeNode p = replacementTreeNode(e, null); // 将Node类型的节点e替换为TreeNode类型的p
if (tl == null)
hd = p; // 若当前链表为空，则赋值头指针为p
else {
p.prev = tl; // 否则将p添加到链表尾部
tl.next = p;
}
tl = p; // 后移尾指针
} while ((e = e.next) != null); // 循环继续
if ((tab[index] = hd) != null) // 将链表头节点放入table的index位置
hd.treeify(tab); // 通过treeify方法将链表树化
}
}
/**
* Copies all of the mappings from the specified map to this map.
* These mappings will replace any mappings that this map had for
* any of the keys currently in the specified map.
*
* @param m
* mappings to be stored in this map
* @throws NullPointerException
* if the specified map is null
*/
public void putAll(Map m) {
putMapEntries(m, true);
}
/**
* Removes the mapping for the specified key from this map if present.
*
* @param key
* key whose mapping is to be removed from the map
* @return the previous value associated with key, or
* null if there was no mapping for key.
* (A null return can also indicate that the map
* previously associated null with key.)
*/
public V remove(Object key) {
Node e;
return (e = removeNode(hash(key), key, null, false, true)) == null ? null : e.value;
}
/**
* Implements Map.remove and related methods
* 提供内remove方法使用
*
* @param hash
* hash for key
* @param key
* the key
* @param value
* the value to match if matchValue, else ignored
* @param matchValue
* if true only remove if value is equal
* @param movable
* if false do not move other nodes while removing
* @return the node, or null if none
*/
final Node removeNode(int hash, Object key, Object value,
boolean matchValue, boolean movable) {
Node[] tab;
Node p;
int n, index;
if ((tab = table) != null && (n = tab.length) > 0 &&
(p = tab[index = (n - 1) & hash]) != null) {
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) {
// tree情况
if (p instanceof TreeNode)
node = ((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 TreeNode)
((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;
}
/**
* Removes all of the mappings from this map.
* The map will be empty after this call returns.
*/
public void clear() {
Node[] tab;
modCount++;
if ((tab = table) != null && size > 0) {
size = 0;
for (int i = 0; i < tab.length; ++i)
tab[i] = null;
}
}
/**
* Returns true if this map maps one or more keys to the
* specified value.
*
* @param value
* value whose presence in this map is to be tested
* @return true if this map maps one or more keys to the
* specified value
*/
public boolean containsValue(Object value) {
Node[] tab;
V v;
if ((tab = table) != null && size > 0) {
for (int i = 0; i < tab.length; ++i) {
for (Node e = tab[i]; e != null; e = e.next) {
if ((v = e.value) == value ||
(value != null && value.equals(v)))
return true;
}
}
}
return false;
}
/**
* Returns a {@link Set} view of the keys contained in this map.
* The set is backed by the map, so changes to the map are
* reflected in the set, and vice-versa. If the map is modified
* while an iteration over the set is in progress (except through
* the iterator's own remove operation), the results of
* the iteration are undefined. The set supports element removal,
* which removes the corresponding mapping from the map, via the
* Iterator.remove, Set.remove,
* removeAll, retainAll, and clear
* operations. It does not support the add or addAll
* operations.
*
* @return a set view of the keys contained in this map
*/
public Set keySet() {
Set ks;
return (ks = keySet) == null ? (keySet = new KeySet()) : ks;
}
final class KeySet extends AbstractSet {
public final int size() {
return size;
}
public final void clear() {
HashMap.this.clear();
}
public final Iterator 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 spliterator() {
return new KeySpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer action) {
Node[] 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 e = tab[i]; e != null; e = e.next)
action.accept(e.key);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
/**
* Returns a {@link Collection} view of the values contained in this map.
* The collection is backed by the map, so changes to the map are
* reflected in the collection, and vice-versa. If the map is
* modified while an iteration over the collection is in progress
* (except through the iterator's own remove operation),
* the results of the iteration are undefined. The collection
* supports element removal, which removes the corresponding
* mapping from the map, via the Iterator.remove,
* Collection.remove, removeAll,
* retainAll and clear operations. It does not
* support the add or addAll operations.
*
* @return a view of the values contained in this map
*/
public Collection values() {
Collection vs;
return (vs = values) == null ? (values = new Values()) : vs;
}
final class Values extends AbstractCollection {
public final int size() {
return size;
}
public final void clear() {
HashMap.this.clear();
}
public final Iterator iterator() {
return new ValueIterator();
}
public final boolean contains(Object o) {
return containsValue(o);
}
public final Spliterator spliterator() {
return new ValueSpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer action) {
Node[] 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 e = tab[i]; e != null; e = e.next)
action.accept(e.value);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
/**
* Returns a {@link Set} view of the mappings contained in this map.
* The set is backed by the map, so changes to the map are
* reflected in the set, and vice-versa. If the map is modified
* while an iteration over the set is in progress (except through
* the iterator's own remove operation, or through the
* setValue operation on a map entry returned by the
* iterator) the results of the iteration are undefined. The set
* supports element removal, which removes the corresponding
* mapping from the map, via the Iterator.remove,
* Set.remove, removeAll, retainAll and
* clear operations. It does not support the
* add or addAll operations.
*
* @return a set view of the mappings contained in this map
*/
public Set> entrySet() {
Set> es;
return (es = entrySet) == null ? (entrySet = new EntrySet()) : es;
}
final class EntrySet extends AbstractSet> {
public final int size() {
return size;
}
public final void clear() {
HashMap.this.clear();
}
public final Iterator> 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 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 EntrySpliterator<>(HashMap.this, 0, -1, 0, 0);
}
public final void forEach(Consumer> action) {
Node[] 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 e = tab[i]; e != null; e = e.next)
action.accept(e);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
}
// Overrides of JDK8 Map extension methods
@Override
public V getOrDefault(Object key, V defaultValue) {
Node e;
return (e = getNode(hash(key), key)) == null ? defaultValue : e.value;
}
@Override
public V putIfAbsent(K key, V value) {
return putVal(hash(key), key, value, true, true);
}
@Override
public boolean remove(Object key, Object value) {
return removeNode(hash(key), key, value, true, true) != null;
}
@Override
public boolean replace(K key, V oldValue, V newValue) {
Node e;
V v;
if ((e = getNode(hash(key), key)) != null &&
((v = e.value) == oldValue || (v != null && v.equals(oldValue)))) {
e.value = newValue;
afterNodeAccess(e);
return true;
}
return false;
}
@Override
public V replace(K key, V value) {
Node 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);
Node[] tab;
Node first;
int n, i;
int binCount = 0;
TreeNode t = null;
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 TreeNode)
old = (t = (TreeNode) first).getTreeNode(hash, key);
else {
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;
}
}
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;
}
public V computeIfPresent(K key,
BiFunction remappingFunction) {
if (remappingFunction == null)
throw new NullPointerException();
Node e;
V oldValue;
int hash = hash(key);
if ((e = getNode(hash, key)) != null &&
(oldValue = e.value) != null) {
V v = remappingFunction.apply(key, oldValue);
if (v != null) {
e.value = v;
afterNodeAccess(e);
return v;
} else
removeNode(hash, key, null, false, true);
}
return null;
}
@Override
public V compute(K key,
BiFunction remappingFunction) {
if (remappingFunction == null)
throw new NullPointerException();
int hash = hash(key);
Node[] tab;
Node first;
int n, i;
int binCount = 0;
TreeNode t = null;
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 TreeNode)
old = (t = (TreeNode) first).getTreeNode(hash, key);
else {
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;
V v = remappingFunction.apply(key, oldValue);
if (old != null) {
if (v != null) {
old.value = v;
afterNodeAccess(old);
} else
removeNode(hash, key, null, false, true);
} else if (v != null) {
if (t != null)
t.putTreeVal(this, tab, hash, key, v);
else {
tab[i] = newNode(hash, key, v, first);
if (binCount >= TREEIFY_THRESHOLD - 1)
treeifyBin(tab, hash);
}
++modCount;
++size;
afterNodeInsertion(true);
}
return v;
}
@Override
public V merge(K key, V value,
BiFunction remappingFunction) {
if (value == null)
throw new NullPointerException();
if (remappingFunction == null)
throw new NullPointerException();
int hash = hash(key);
Node[] tab;
Node first;
int n, i;
int binCount = 0;
TreeNode t = null;
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 TreeNode)
old = (t = (TreeNode) first).getTreeNode(hash, key);
else {
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)
v = remappingFunction.apply(old.value, value);
else
v = value;
if (v != null) {
old.value = v;
afterNodeAccess(old);
} else
removeNode(hash, key, null, false, true);
return v;
}
if (value != null) {
if (t != null)
t.putTreeVal(this, tab, hash, key, value);
else {
tab[i] = newNode(hash, key, value, first);
if (binCount >= TREEIFY_THRESHOLD - 1)
treeifyBin(tab, hash);
}
++modCount;
++size;
afterNodeInsertion(true);
}
return value;
}
@Override
public void forEach(BiConsumer action) {
Node[] 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 e = tab[i]; e != null; e = e.next)
action.accept(e.key, e.value);
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
@Override
public void replaceAll(BiFunction function) {
Node[] 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 e = tab[i]; e != null; e = e.next) {
e.value = function.apply(e.key, e.value);
}
}
if (modCount != mc)
throw new ConcurrentModificationException();
}
}
/* ------------------------------------------------------------ */
// Cloning and serialization
/**
* Returns a shallow copy of this HashMap instance: the keys and
* values themselves are not cloned.
*
* @return a shallow copy of this map
*/
@SuppressWarnings("unchecked")
@Override
public Object clone() {
HashMap result;
try {
result = (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;
}
/**
* Save the state of the HashMap instance to a stream (i.e.,
* serialize it).
*
* @serialData The capacity of the HashMap (the length of the
* bucket array) is emitted (int), followed by the
* size (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);// table长度
s.writeInt(size);// 只需要写入全部元素,部需要记录table上无元素的情况
internalWriteEntries(s);// 写入元素
}
/**
* Reconstitute the {@code HashMap} instance from a stream (i.e.,
* deserialize it).
* 反序列化使用,在反序列化时系统会调用到这个方法.依次读出writeObject写入的内容
*/
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[] tab = (Node[]) 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 next; // next entry to return
Node current; // current entry
int expectedModCount; // for fast-fail
int index; // current slot
HashIterator() {
expectedModCount = modCount;
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 Node nextNode() {
Node[] t;
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() {
Node 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 {
public final K next() {
return nextNode().key;
}
}
final class ValueIterator extends HashIterator
implements Iterator {
public final V next() {
return nextNode().value;
}
}
final class EntryIterator extends HashIterator
implements Iterator> {
public final Map.Entry next() {
return nextNode();
}
}
/* ------------------------------------------------------------ */
// spliterators
static class HashMapSpliterator {
final HashMap map;
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(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) {
HashMap m = map;
est = m.size;
expectedModCount = m.modCount;
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 HashMapSpliterator
implements Spliterator {
KeySpliterator(HashMap m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public KeySpliterator 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 action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap m = map;
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)) {
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();
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 HashMapSpliterator
implements Spliterator {
ValueSpliterator(HashMap m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public ValueSpliterator 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 action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap m = map;
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)) {
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();
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 HashMapSpliterator
implements Spliterator> {
EntrySpliterator(HashMap m, int origin, int fence, int est,
int expectedModCount) {
super(m, origin, fence, est, expectedModCount);
}
public EntrySpliterator 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> action) {
int i, hi, mc;
if (action == null)
throw new NullPointerException();
HashMap m = map;
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)) {
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();
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 {
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
/*
* 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 newNode(int hash, K key, V value, Node next) {
return new Node<>(hash, key, value, next);
}
// For conversion from TreeNodes to plain nodes
Node replacementNode(Node p, Node next) {
return new Node<>(p.hash, p.key, p.value, next);
}
// Create a tree bin node
TreeNode newTreeNode(int hash, K key, V value, Node next) {
return new TreeNode<>(hash, key, value, next);
}
// For treeifyBin
TreeNode replacementTreeNode(Node p, Node 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 p) {
}
void afterNodeInsertion(boolean evict) {
}
void afterNodeRemoval(Node p) {
}
// Called only from writeObject, to ensure compatible ordering.
// 全部元素
void internalWriteEntries(java.io.ObjectOutputStream s) throws IOException {
Node[] tab;
if (size > 0 && (tab = table) != null) {
for (int i = 0; i < tab.length; ++i) {
for (Node 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.
* 树结构节点,继承LinkedHashMap.Entry
*/
static final class TreeNode extends LinkedHashMap.Entry {
// 父,左右子,颜色
TreeNode parent; // red-black tree links
TreeNode left;
TreeNode right;
TreeNode prev; // needed to unlink next upon deletion
boolean red;
TreeNode(int hash, K key, V val, Node next) {
super(hash, key, val, next);
}
/**
* Returns root of tree containing this node.
*/
final TreeNode root() {
for (TreeNode 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 void moveRootToFront(Node[] tab, TreeNode root) {
int n;
if (root != null && tab != null && (n = tab.length) > 0) {
int index = (n - 1) & root.hash;
TreeNode first = (TreeNode) tab[index];
if (root != first) {
Node rn;
tab[index] = root;
TreeNode rp = root.prev;
if ((rn = root.next) != null)
((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);
}
}
/**
* 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 find(int h, Object k, Class kc) {
TreeNode p = this;
do {
int ph, dir;
K pk;
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;
}
/**
* Calls find for root node.
* 查找树中元素 -> 从root开始
*/
final TreeNode getTreeNode(int h, Object k) {
// root的parent==null
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.
* 两节点hashcode相同无法排序时,用System.identityHashCode再进行依次比较
* identityHashCode 使用内存地址进行hashCode
*/
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
* 真正转变操作
*/
// 这是TreeNode类的实例方法，以调用节点this为根节点，将链表树化
final void treeify(Node[] tab) {
TreeNode root = null; // 声明root变量以记录根节点
for (TreeNode x = this, next; x != null; x = next) { // 从调用节点this开始遍历
next = (TreeNode) x.next; // 暂存链表中的下一个节点，记为next
x.left = x.right = null; // 当前节点x的左右子树置空
if (root == null) {
x.parent = null; // 若root仍为空，则将x节点作为根节点
x.red = false; // 红黑树特性之一：根节点为黑色
root = x; // 赋值root
} else { // 否则的话需将当前节点x插入到已有的树中
K k = x.key;
int h = x.hash;
Class kc = null;
// 第二层循环，从根节点开始寻找适合x插入的位置，并完成插入操作。
// putTreeVal方法的实现跟这里十分相似。
for (TreeNode p = root;;) {
int dir, ph;
K pk = p.key;
if ((ph = p.hash) > h) // 若x的hash值小于节点p的，则往p的左子树中继续寻找
dir = -1;
else if (ph < h) // 反之在右子树中继续
dir = 1;
// 若两节点hash值相等，且key不可比，则利用System.identityHashCode方法来决定一个方向
else if ((kc == null && (kc = comparableClassFor(k)) == null) ||
(dir = compareComparables(kc, k, pk)) == 0)
dir = tieBreakOrder(k, pk);
TreeNode xp = p; // 将当前节点p暂存为xp
// 根据上面算出的dir值将p向下移向其左子树或右子树，若为空，则说明找到了合适的插入位置，否则继续循环
if ((p = (dir <= 0) ? p.left : p.right) == null) {
// 执行到这里说明找到了合适x的插入位置
x.parent = xp; // 将x的parent指针指向xp
if (dir <= 0) // 根据dir决定x是作为xp的左孩子还是右孩子
xp.left = x;
else
xp.right = x;
// 由于需要维持红黑树的平衡，即始终满足其5条性质，每一次插入新节点后都需要做平衡操作
// 这个方法的源码我们在<<红黑树(Red-Black Tree)解析>>一文中已有详细分析，此处不再重复
root = balanceInsertion(root, x);
break; // 插入完成，跳出循环
}
}
}
}
// 由于插入后的平衡调整可能会更换整棵树的根节点，
// 这里需要通过moveRootToFront方法确保table[index]中的节点与插入前相同
moveRootToFront(tab, root);
}
/**
* Returns a list of non-TreeNodes replacing those linked from
* this node.
*/
final Node untreeify(HashMap map) {
Node hd = null, tl = null;
for (Node q = this; q != null; q = q.next) {
Node p = map.replacementNode(q, null);
if (tl == null)
hd = p;
else
tl.next = p;
tl = p;
}
return hd;
}
/**
* Tree version of putVal.
*/
final TreeNode putTreeVal(HashMap map, Node[] tab,
int h, K k, V v) {
Class kc = null;
boolean searched = false;
TreeNode root = (parent != null) ? root() : this;
for (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) {
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);
}
TreeNode xp = p;
if ((p = (dir <= 0) ? p.left : p.right) == null) {
Node xpn = xp.next;
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)
((TreeNode) 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 map, Node[] tab,
boolean movable) {
int n;
if (tab == null || (n = tab.length) == 0)
return;
int index = (n - 1) & hash;
TreeNode first = (TreeNode) tab[index], root = first, rl;
TreeNode succ = (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 || root.right == null ||
(rl = root.left) == null || rl.left == null) {
tab[index] = first.untreeify(map); // too small
return;
}
TreeNode p = this, pl = left, pr = right, replacement;
if (pl != null && pr != null) {
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
TreeNode sr = s.right;
TreeNode pp = p.parent;
if (s == pr) { // p was s's direct parent
p.parent = s;
s.right = p;
} else {
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) {
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;
}
TreeNode r = p.red ? root : balanceDeletion(root, replacement);
if (replacement == p) { // detach
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);
}
/**
* 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.
* 修剪或转成链表
*
* @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 map, Node[] tab, int index, int bit) {
TreeNode b = this;
// Relink into lo and hi lists, preserving order
TreeNode loHead = null, loTail = null;
TreeNode hiHead = null, hiTail = null;
int lc = 0, hc = 0;
for (TreeNode e = b, next; e != null; e = next) {
next = (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) {
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
// 旋转
static TreeNode rotateLeft(TreeNode root,
TreeNode p) {
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 TreeNode rotateRight(TreeNode root,
TreeNode p) {
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 TreeNode balanceInsertion(TreeNode root,
TreeNode x) {
x.red = true;
for (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 TreeNode balanceDeletion(TreeNode root,
TreeNode x) {
for (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 {
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 {
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;
}
}
}
}
}
/**
* Recursive invariant check
*/
static boolean checkInvariants(TreeNode
