hashMap解读1

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 t) { TreeNode tp = t.parent, tl = t.left, tr = t.right, tb = t.prev, tn = (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; } } }

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